Home Blog

Advanced Crop Nutrition Management by Utilizing Continuous Fertigation

By
Devin Clarke | PCA, CCA, Agronomy Solutions Manager, Yara North America
-
0
Trees do not require nutritional support in large amounts at discrete periods of time. They are continuously supporting various physiological activities and have been shown to benefit from continuous fertigation crop nutrition management that more closely aligns supply with incremental demand (photo by Taylor Chalstrom.)

Over 90% of all almond acres farmed in California are using fertigation to deliver crop nutrition. How-ever, the statewide average for nitrogen use efficiency is still around 70%. This value of 70% efficiency means we are essentially wasting around 65 lb of nitrogen per acre per year on a 2,200-lb crop. Additionally, there are negative environmental outcomes associated with these losses in the form of ground-water leaching and emissions.

Why does this demand and supply gap still exist using this more efficient management strategy? Well, we still lack a robust and accurate means for yield prediction, but more fundamentally, we’re fertigating ineffectively.

Looking at the newest UC Davis Cost Studies from 2024, the assumption used is that still, UAN-32 is applied monthly from March through May, then one additional postharvest application. This equates to 25% of the N budget being applied in each of four intervals. Let’s put this in context of another living organism. An average adult human being requires roughly a 2000-calorie daily intake or 14,000 calories per week. We could assume negative consequences would arise if that adult consumed all their weekly caloric needs in four sittings. A tree is no different in that it does not require nutritional support in large amounts at discrete periods of time. They are continuously supporting various physiological activities and have been shown to benefit from continuous fertigation crop nutrition management that more closely aligns supply with incremental demand.

What is Continuous Fertigation?
The management of crop nutrition by continuous fertigation is centered around delivering smaller amounts of fertilizer more frequently using irrigation water as a carrier. This usually takes the form of weekly or even sub-weekly fertigation events depending on irrigation system infrastructure and orchard characteristics. The rates at each interval should also align with the perceived demand. Most discussions on continuous fertigation typically pertain to N management due to characteristics of various forms and potential for loss.

Yara North America’s Incubator Farm in Modesto, Calif. has been trialing continuous fertigation in almond for five years.

How Continuous Fertigation is Implemented

At the field site
Although any irrigation/fertigation system can be utilized to perform continuous fertigation, a more sophisticated infrastructure that enables scheduling, monitoring and recording of individual events is typically required to mitigate labor constraints that are associated with physically executing applications. Individual events are most efficiently managed by remote scheduling.

There are many competing manufacturers in this irrigation and fertigation service provider space. When choosing the right equipment, don’t be fooled by all the fancy analytics and visuals. What’s most important is that you have the right combination of hardware and software interface for your needs. It should be adapted to your current system configuration, align with your workflow, reduce labor associated with fertigation operations, provide the right sensors and alarms to keep your system operational and be user-friendly to enable the seamless execution of your desired management strategy. In many cases, we see companies that get either the hardware right or the software interface right. There are only a few that get both.

Though this management style is best suited for well water applications due to control of the availability of water for prescheduling irrigation events, those stations operating by surface water delivery can typically plan with their ditch tenders to set block-by-block irrigation schedules accordingly. Once an irrigation event is planned or scheduled, growers can align the injection event with the irrigation based on soil type, soil conditions and the crop nutrition input source. As a general rule, nitrate and urea N sources move equally with water and thus should be positioned closer to the end of the irrigation event than an ammoniacal input source. It is also important to be aware of the soil type and conditions when deciding how long to flush the system after the fertilizer has been injected. The longer the flush, the greater chance of moving N past the rootzone. Injecting a spray indicator dye and observing coloration at various downstream points after an injection event is one way of determining how long your system should be flushed to ensure all materials are out of the system.

If the size of the field being serviced is over 40 ac, you will want to have the capacity to pump at least 100 gph (200 gph if over 100 ac) volume through your pump system to enable short duration fertigation events early in the growing season when transpiration rates are low but N demand is high. Lower rates can be used but impact the duration of input fertigation and may lead to injections that must start earlier than halfway through the irrigation set and potentially lead to greater leaching risks. For storage, one to two liquid tanks are required per station depending on compatibility of prescribed inputs or blends and field size.

As a grower, you need to work with a trusted and knowledgeable advisor who can provide a prescription for the appropriate inputs and rates at each event to match demand, manage chemical incompatibilities, mitigate blend “fall-out” (precipitation of minerals in fertilizer blend over time) and make in-season adaptations when necessary.       

Planning
Developing a seasonal plan is paramount to successful execution. As a grower, you’ll need a weekly schedule with specified inputs or blends, per-acre rates and per-set totals because your events will typically be scheduled by irrigation block.

As an advisor, developing a weekly schedule is more than just taking the seasonal N needs and dividing those evenly by the number of applications, then applying a specific product at a specific time. All your agronomy training, especially the 4Rs, is utilized in developing this type of recommendation.

It begins with a keen understanding of the demand curve. The rate of tree N demand is greatest between leaf-out and fruit development (sizing), then slows just a bit through kernel fill and then tapers off more as nuts reach maturity and through to senescence. Weekly rates should mirror this demand curve. The Almond Board of California has a good visual of this in their Nitrogen Best Management Practices handout.

Once you dial in the rates, you need to be aware of the abiotic conditions and physiological events taking place at various points through the season to choose the best input source to fulfill nutrient demand. Soil temperature, for one, is a significant factor. At Yara’s Incubator Farm in Modesto, Calif., we have a sandy loam soil that averaged about 56F between the middle of March and the middle of April. According to the Western Fertilizer Handbook, 2012, full conversion from ammoniacal nitrogen to plant-available nitrate N would be somewhere between six and nine weeks. To accurately match demand, you need to be aware of the time associated with nitrification rates. Just because we apply crop nutrition products to the field site doesn’t mean the plant can always access them. When inputs are not readily available to the plant, an unintended lag between application time and actual plant uptake may occur. In these earlier-season fertigation events, inputs with a higher percentage of nitrate N can ensure plant uptake as this form of nitrogen is fully plant-available regardless of soil temperature.

Results from a five-year continuous fertigation trial in almond by Yara North America show a $630/ac net profitability increase compared to “slug”-based grower standard programs supported by a 17% yield increase. The crop output per ac-inch of water improved almost 15%, and the fertilizer carbon footprint was reduced by 10%.

Why Continuous Fertigation Should Be Implemented
Though it may appear complex at first glance, continuous fertigation is fairly simple to adopt with the right tools and a knowledgeable advisor. It can be a far more prescriptive strategy that requires less guesswork when utilized properly. With regular field visits and tissue sampling efforts, it is easy to make minor adjustments along the way instead of only having basically three opportunities during the development of the crop to get it right.

There are several other key benefits to adopting a continuous fertigation strategy in almond. The first is profitability. There is absolutely a cost to nitrogen use efficiency (NUE). If the nitrogen applied does not generate greater output, then the dollars spent for those units of N are wasted, not to mention they’re environmental fate is likely further degradation of our groundwater resources and a recipe for further regulations.

To address NUE economics, let’s consider a 2200-lb/ac crop example. To save money, you can you cut 50 lbs N/ac and save roughly $30/ac, but you will need to increase from 70% to 90% NUE to maintain yields. However, consider the opportunity costs. If you maintain the same N rates and improve from 70% to 90% NUE, you now have the ability to support another 700 kernel lbs/ac. Now we’re making money instead of just saving.

That’s all just math though; how does this actually perform in real-world conditions?

Through good economic years and bad, we have been trialing continuous fertigation combined with higher nitrate N programs for the last five years at the Incubator Farm and externally. Over those five years, we have documented a $630/ac net profitability increase compared to a “slug”-based grower standard program supported by a 17% yield increase. The environmental impact of these programs is also reduced. The crop output per ac-inch of water has improved almost 15%, and the fertilizer carbon footprint has been reduced by 10%.

These results combined support a strong argument for continuous fertigation adoption by highlighting the gains in efficiency of production, resulting in greater productivity, profitability and input resource optimization.

Monitoring and Building Soil Health in California Vineyards

By
Charlotte Decock | Associate Professor, Dept. of Natural Resources Management and Environmental Sciences, California Polytechnic State University, San Luis Obispo, Lauren Picone | Masters Student, Environmental Sciences and Management, California Polytechnic State University, San Luis Obispo, Priya Verma | Associate Professor, Dept. of Natural Resources Management and Environmental Sciences, California Polytechnic State University, San Luis Obispo, Matt Grieshop | Director, Grimm Family Center for Organic Production and Research, California Polytechnic State University and Cristina Lazcano | Associate Professor, Dept. of Land, Air and Water Resources, UC Davis
-
0
Figure 1. Example of a vineyard soil health scoring function modeled after Cornell’s CASH framework.

Soil health is central to sustainable agriculture and a key goal of regenerative and organic farming. Practices like the application of organic amendments, cover cropping, reduced tillage and livestock integration are promoted to improve soil health. Traditionally, sustainability or organic certifications have relied on the adoption of certain practices for monitoring and verification. However, newer regenerative agriculture certifications are introducing requirements for direct monitoring of soil health.

This shift raises important questions: How should soil health be measured and rated? How can these ratings inform management decisions? Should soil health ratings and interpretations be tailored to specific crops and regions?

To explore these issues, we conducted a case study analysis of 87 vineyard blocks across California, representing diverse management histories. This study aims to shed light on the link between regenerative agriculture and soil health monitoring in the context of California winegrape production.

Figure 2. Map of participating vineyard blocks and sample locations. A total of 87 vineyard blocks were sampled from as far north as the Russian River Valley AVA and down to the Happy Canyon of Santa Barbara AVA.

How to Measure Soil Health?
Numerous soil health assessment frameworks have been developed globally, each varying in practicality, sensitivity, and interpretability. These frameworks typically include indicators of physical, chemical and biological soil properties. In the U.S., commercial laboratories offer soil health testing packages priced between $55 to $165 per sample. However, the methods and indicators used in these packages vary, making it challenging to compare results across tests.

The Soil Health Institute evaluated 30 soil health indicators across 124 long-term experiments in Northern America and recommended a core suite of practical and affordable measurements: soil organic carbon (SOC), carbon mineralization potential (MinC) and aggregate stability index (ASI). These indicators were chosen for their response to management practices across a wide range of soils, climates and production systems. In our study, we focused on these three indicators due to growing interest among California growers and laboratories in the Soil Health Institute’s recommendations.

Interpreting Soil Health Measurements
When evaluating soil health indicators, it is common to wonder: Is a MinC value of 50 mg CO2-C/kg soil/day  good or bad? Last year, my soil had 1.2% SOC, but this year, the lab results showed 1.15%. Does this indicate a significant decline in soil health? What is the maximum aggregate stability achievable in my soil?

Answering these questions requires an understanding of expected soil health indicator ranges, the soil’s inherent potential and typical sampling and analysis errors. To address these complexities, Cornell’s Comprehensive Soil Health Assessment (CASH) developed scoring functions for various soil health indicators using samples from the Mid-Atlantic, Midwest, and Northeast U.S. regions.

The CASH scoring system assigns scores based on the percentage of samples with equal or lower values. For example, a score of 80% means your result is better than 80% of the reference dataset (Fig. 1). The system also accounts for soil texture, recognizing its role in influencing and sometimes constraining soil health outcomes.

Color ranges on the chart help evaluate whether soil health values differ significantly. Substantial improvements over time can shift soil into better color zones, with dark green zone indicating the soil has likely reached its potential. Though other rating and benchmarking frameworks have been proposed, we based our scoring system for California vineyards on the CASH framework, given its simplicity and clarity.

Rating Curves for California Vineyards
To develop scoring functions for California vineyards, we collaborated with winegrape growers who provided soil samples from vineyard blocks of red varietals. These blocks included those that had adopted cover cropping, compost application and no till or grazing for at least five years as well as blocks where none of these practices had been adopted for at least 10 years. Soil samples were collected from areas next to the vine and at the center of the drive rows. Additionally, growers completed a detailed survey about their practice implementation.

The dataset includes a total of 87 vineyard blocks (Fig. 2), with various combinations of practice adoption, ranging between 0 and 27 years. Thus, the scoring functions represent how soil health values may improve with the adoption of regenerative practices across a broad range of soil types and microclimates (Fig. 3).

Figure 3. Soil health scoring functions for soil organic carbon (SOC), mineralizable carbon (MinC) and aggregate stability index (ASI) for California vineyard soils

Like other frameworks, our scoring functions account for soil texture. Clayey soils are known to store more carbon and support greater microbial activity compared to sandier soils. Consequently, coarse-textured soils achieve high scores at lower SOC and MinC values than fine-textured soils. For ASI, values trend higher in coarse-textured soils because they are less prone to dispersion when slaked.

Comparing the ranges of SOC, MinC and ASI in our study to those reported in the literature supports the idea that building soil health may face more biophysical limitations in mediterranean regions compared to temperate climate zones. This highlights the importance of developing scoring functions tailored to specific regions and crops.

Monitoring Soil Health for Adaptive Management
For soil health scoring systems to be useful for growers, they must be sensitive to changes in management practices within an operation. To test this, we compiled individualized reports for each participating grower and evaluated whether the scoring system could detect differences in management history among samples from the same grower (Fig. 3).

The study involved 12 growers, each providing samples from 2 to 17 vineyard blocks. Overall, the scoring system successfully identified differences between vineyard blocks submitted by the same grower. Growers reported the scores either reinforced their management goals or highlighted areas where soil health management fell short of their targets. These findings demonstrate the soil health assessment framework can effectively support adaptive soil management in vineyards (Fig. 4).

Figure 4. Anonymized grower report example. Soil health ratings are greater in the vineyard blocks with adoption of multiple practices compared to vineyard blocks with only cover crops.

Successful Paths to a Healthy Vineyard Soil
Adopting soil health practices, such as cover cropping, composting, reduced tillage and grazing, involves costs and uncertainties, often with unclear timelines for measurable impacts. We used quantitative comparative analysis to explore conditions leading to soil health scores above 60%, revealing complex causal relationships.

Long-term cover cropping (10+ years) emerged as the most important factor for achieving high soil health scores, especially when combined with another regenerative practice. This benefit extended across the vineyard floor, improving soil health in both alleys and under-vine areas. Notably, the integration of livestock was identified as a key practice for accelerating soil health improvements, yielding measurable benefits even after less than 10 years of cover cropping.

Achieving high ASI and MinC scores appeared to require long-term adoption of more practices compared to high SOC scores. However, our findings suggest tailoring the right combination of practices to specific environmental conditions is more important than simply increasing the number of practices used.

Practical Implications for Vineyard Managers in California
Our study provides proof-of-concept for the use of SOC, MinC and ASI to evaluate vineyard soil health in California, supported by practical soil health scoring functions. This approach can help monitor vineyard soil health and inform adaptive management strategies. Given the variability of soil type and microclimate, growers are encouraged to experiment with different strategies to determine what works best for their conditions. While monitoring can identify effective practices, building soil health is a slow process that often takes over a decade. This underscores the need for long-term commitment, with monitoring intervals every few years being sufficient.

Winegrape growers can use our rating curves as a reference to monitor soil health. For SOC testing, ensure that labs report SOC specifically, rather than total carbon, especially in calcareous soils where high carbonates can skew results. Many labs also offer MinC (soil respiration) testing; our scoring functions are applicable as long as results are expressed in mg CO₂-C kg–¹ soil d–¹, regardless of preparation or incubation duration (one to four days). For ASI, only results obtained using the Soil Health Institute’s SLAKES test are compatible with our scoring functions. Growers can work with labs that use SLAKES or measure ASI in-house via the SLAKES app available at soilhealthinstitute.org/our-work/initiatives/slakes/.

Future Work
The scoring functions in our study are based on data from 87 vineyard blocks and reflect the progression in soil health scores that may occur over time with the implementation of a soil health management strategy. As more data becomes available, these scoring functions could be refined further to address specific soil types or microclimates.

Since the effectiveness of soil health management practices depends on factors like implementation (e.g., cover crop species, compost type, etc.) as well as soil type and environmental conditions, future research should focus on identifying the most effective combinations of practices for specific contexts.

Finally, soil health is rarely a management goal on its own. Future research should quantify the impact of improved soil health on key agronomic and environmental outcomes, including yield, grape quality, pest and disease pressure, pollution from leaching and runoff, biodiversity and climate change adaptation and mitigation.

This project was funded by the CDFA Specialty Crops Block Grant and the Foundation for Food and Agriculture Research. We thank all growers who participated in this study.

References
Hughes, H. M. et al. Towards a farmer-feasible soil health assessment that is globally applicable. Journal of Environmental Management 345, 118582 (2023).

Feeney, C. J. et al. Development of soil health benchmarks for managed and semi-natural landscapes. Science of The Total Environment 886, 163973 (2023).

Bünemann, E. B. Soil quality – A critical review. Soil Biology and Biochemistry 120, 105–125 (2018).

Shi. Recommended Measurements for Scaling Soil Health Assessment. (2024).

Fine, A. K., van Es, H. M. & Schindelbeck, R. R. Statistics, scoring functions, and regional analysis of a comprehensive soil health database. Soil Science Society of America Journal 81, 589–601 (2017).

Moebius-Clune, B. N. et al. Comprehensive Assessment of Soil Health – The Cornell Framework Manual. (2016).

Maharjan, B., Das, S. & Acharya, B. S. Soil Health Gap: A concept to establish a benchmark for soil health management. Global Ecology and Conservation 23, e01116 (2020).

Six, J., Doetterl, S., Laub, M., Müller, C. R. & Van de Broek, M. The six rights of how and when to test for soil C saturation. SOIL 10, 275–279 (2024).

Müller, T. & Höper, H. Soil organic matter turnover as a function of the soil clay content: consequences for model applications. Soil Biology and Biochemistry 36, 877–888 (2004).

Nunes, M. R. et al. SHAPEv1.0 Scoring curves and peer group benchmarks for dynamic soil health indicators. Soil Science Society of America Journal 88, 858–875 (2024).

Fajardo, M., McBratney, Alex. B., Field, D. J. & Minasny, B. Soil slaking assessment using image recognition. Soil and Tillage Research 163, 119–129 (2016).

Slakes: A Free Smartphone App to Measure Aggregate Stability. Soil Health Institute (2024). https://soilhealthinstitute.org/our-work/initiatives/slakes/#overview

Citrus Dry Root Rot Caused by Fusarium solani: A Persistent Threat to California Citrus

By
Fatemeh Khodadadi | Assistant Professor of Cooperative Extension, Dept. of Microbiology and Plant Pathology, UC Riverside, Zahra Pegahrad, Lab Assistant, Dept. of Microbiology and Plant Pathology, UC Riverside and Mehdi Kamali Dashtarzhaneh | Dept. of Microbiology and Plant Pathology, UC Riverside
-
0
Figure 1. Dry root rot disease in lemon orchard planted on Carrizo in Santa Paula. a) Lemon trees with yellow foliage; b) impacted crown, roots and vascular system and usually abundant fruit fallen over from dry root rot; c) wilted dead tree.

 

Dry root rot, caused by the soilborne fungus Fusarium solani, has been a persistent threat to California citrus for decades. While the disease has been preent in citrus orchards for many years, it became particularly problematic following wet winters in the 1960s and 1980s. During these periods, the disease affected both young and mature trees, especially those on susceptible rootstocks and in poorly drained soils. However, the threat of dry root rot persists today, posing an ongoing challenge to California’s citrus industry.

Fusarium solani
F. solani is a weak pathogen that requires a weakened host to cause significant damage. Factors like stress from other pathogens, nutrient deficiencies or environmental stressors can predispose citrus trees to infection. For example, Phytophthora root rot can weaken trees, making them more susceptible to F. solani attack. Trees planted as bare-root seedlings exhibited higher resistance to dry root rot compared to container-grown trees. However, fumigation prior to planting was associated with reduced disease incidence. Several factors can contribute to the development of dry root rot in citrus; a combination of environmental and host factors can predispose citrus trees to Fusarium solani infection. Periods of drought or excessive moisture can weaken trees, making them more susceptible to disease. High temperatures can exacerbate symptoms and promote fungal growth. Poor soil drainage and nutrient imbalances can further compromise tree health. Host factors also play a significant role. Certain rootstocks may exhibit greater susceptibility to F. solani infection compared to others. Older trees with declining vigor may be more prone to infection. The virulence of specific F. solani strains and the level of inoculum present in the soil can influence the severity of disease outbreaks. By understanding these complex interactions, growers can implement targeted management strategies to mitigate the impact of dry root rot on their citrus orchards.

 

Figure 2. Frequency of Phytophthora and Fusarium species isolated from citrus nurseries in California.

Finding the Cause
A comprehensive soil analysis was conducted to assess potential correlations between soil properties and disease incidence. Parameters, such as sodium, boron, salinity, pH and soil type, were evaluated. However, no significant correlations were found between these factors and disease severity. This suggests soil conditions, while important for overall tree health, may not be a primary factor in predisposing trees to dry root rot. Leaf tissue analysis revealed elevated levels of zinc and manganese in diseased trees compared to healthy trees. Additionally, potassium deficiency was observed in diseased trees. However, it is unlikely these nutrient imbalances are the primary cause of the disease. Rather, they may be secondary symptoms resulting from the stress caused by the fungal infection.

F. solani primarily targets the root system, causing a gradual decline in tree health. Infected roots exhibit a characteristic reddish-purple to grayish-black discoloration, which distinguishes it from Phytophthora root rot, which typically affects the outer root bark. This discoloration can extend into the trunk, leading to internal wood decay and external bark discoloration. Aboveground symptoms include leaf yellowing, premature defoliation, twig dieback and reduced fruit yield. In severe cases, trees may suddenly collapse, even with leaves still attached (Fig. 1). 

In the past year, we’ve received numerous reports of healthy lemon trees suddenly wilting and collapsing in Santa Paula, Ventura, and the Central Valley. Upon digging, the root system revealed black, purple or grayish roots with a brown, vascular discoloration. Leaves turned yellow, then brown, with rapid dieback and wilting. Surprisingly, all tree collapses due to dry root rot occurred primarily on lemon trees planted on Carrizo citrange rootstock. Adjacent lemon blocks on Trifoliate or C-35 rootstocks remained unaffected despite similar management and environmental conditions. These observations led to two hypotheses:

1. Nursery contamination: Multiple sources in nurseries (plants, soil and water) pose a high risk for spreading citrus dry root rot, potentially leading to outbreaks in home gardens and commercial orchards.

2. Rootstock susceptibility: Rootstocks like Carrizo citrange are more susceptible to dry root rot caused by Fusarium solani and Phytophthora species compared to Trifoliate and C-35.

Nurseries can serve as reservoirs for soilborne pathogens like Fusarium and Phytophthora. Infected plant materials, contaminated soil and water sources can harbor these pathogens and facilitate their spread to new orchards. While F. solani is primarily associated with the disease, other fungal pathogens may also be involved. Extensive sampling, identification, pathogenicity testing and characterization of fungal pathogens in all potential nursery sources are essential. In our comprehensive survey of California citrus nurseries, we collected soil, root and water samples. Following rigorous isolation procedures, we identified four key pathogens: F. solani, F. oxysporum, Phytophthora nicotianae, and P. citrophthora. Among these, F. solani was the most prevalent species isolated from nursery samples (Fig. 2).

Morphological examination revealed distinct characteristics for each fungal genus (Fig. 3). These findings emphasize the critical need for stringent sanitation practices and effective disease management strategies within nursery operations to prevent the dissemination of these harmful pathogens.

Selecting a healthy, Fusarium- and Phytophthora-tolerant rootstock is crucial for establishing new orchards as it provides tolerance to the entire plant. Resistant rootstocks play a major role in integrated disease management. Our research is developing an integrated strategy to manage dry root rot and Phytophthora root rot diseases in citrus nurseries and groves. Using resistant rootstocks is a promising approach to combat both diseases. If pre-invasion by Phytophthora is shown to increase dry root rot occurrence, current control methods for Phytophthora could potentially reduce dry root rot incidence in citrus production.

Figure 3. Morphological characteristics of representative species isolated from citrus nursery samples of root tissue and soil belonging to Fusarium and Phytophthora spp. Fusarium colonies were subcultured on potato dextrose media (PDA), while Phytophthora colonies were grown on V8 juice agar. The front (a) and back (b) of media plates were photographed. Under 40x total magnification, multiseptated, oval/kidney-shaped F.solani (c) and multiseptated, oval/kidney-shaped with sharp end on both side F.oxysporum (d) mycelia of Phytophthora spp. under 40X magnification (e, f).

Disease Management Strategies
To effectively manage dry root rot, it is crucial to implement integrated pest management strategies. These may include careful selection of disease-resistant rootstocks, proper irrigation and fertilization practices and the use of fungicides to protect young trees. Additionally, maintaining good orchard sanitation and avoiding excessive soil moisture can help minimize the risk of infection.

Effective management of citrus dry root rot requires a multi-faceted approach. Key strategies include:

1. Disease-free planting material: Sourcing disease-free planting material from reputable nurseries is crucial to prevent the introduction of pathogens into orchards.

2. Soil solarization: Solarizing the soil before planting can help reduce populations of soilborne pathogens, including F. solani.   

3. Cultural practices: Proper irrigation, fertilization, and pruning can enhance tree vigor and reduce susceptibility to disease.

4. Chemical control: Fungicide applications can help manage the disease, but it is important to follow label instructions and rotate fungicides to prevent the development of resistant strains.

5. Biological control: The use of beneficial microorganisms, such as Trichoderma spp., can help suppress the growth of F. solani and other pathogens.   

By implementing these strategies, citrus growers can mitigate the impact of citrus dry root rot and maintain healthy, productive orchards.

Finding New Insecticides for Use in California Safflower Supported by the IR-4 Program

By
Nick Clark | UCCE Agronomy Advisor, Kings, Tulare and Fresno Counties and Kari Arnold | Associate Director, Western Region IR-4 Project
-
0
Figure 1. Safflower growing as a seedling (top left), in the branching stage of late vegetative growth (top right), and well after flowering (bottom).

Safflower is an oilseed crop with several important uses beyond the valuable oil produced from the harvested seeds (Fig. 1). In the Tulare Lake Basin of the southern San Joaquin Valley in California, safflower is often grown in rotation with processing tomato and cotton. The benefits to the soil that safflower provides to the other crops comes largely from the exceptionally deep taproots that the plant grows, which are highly tolerant of saturated soil conditions. Safflower grown exclusively on residual water from a single preplant irrigation in the winter will draw down a perched water table, which cotton and tomato are sensitive to. Additionally, the taproots of the crop also create deep flow channels for improved water infiltration later in the year which greatly helps with any leaching efforts to remove accumulated salts from the root zone of cotton and tomato planted later.

Aside from the soil and water benefits to cotton and tomato, safflower also plays a key role in pest management in adjacent cotton and tomato fields. Insect pests, such as lygus bug and stink bugs, which are serious pests in tomato and cotton, and beet leafhopper, which transmits Beet Curly Top Virus to tomato, are all found in safflower. As safflower starts growing as early as February, it’s often the only green vegetative plants through April before cotton and tomatoes are planted. That means these insect pests show up on safflower first, and in that vein, safflower acts as an early indicator of the pressures these insects may pose for the upcoming cotton and tomato planted nearby. As cotton and tomato grow early in their seasons and become susceptible to damage from these pests, monitoring of these insect populations in safflower becomes very important to make decisions about areawide insect pest management. To that end, safflower acts as a sort of trap crop for these pests as growers can then treat safflower fields for these insects before they reach development stages and population levels that promote migration into tomato and cotton. This preventative monitoring and treatment in safflower improves pest management success in tomato and cotton by reducing the flow of the pests into these crops, which can then reduce the number of insecticide applications needed in cotton and tomato and preserve those uses for later in the season should they be needed.

Insecticide Trials
Since 2018, we’ve conducted insecticide efficacy and crop safety trials in safflower for control of lygus, stink bugs and beet leafhopper. We compared how well these new insecticides controlled these pests and observed the safflower plants for symptoms of damage from the new insecticides. The purpose of the trials was to generate enough data that is required by the California Department of Pesticide Regulation to show the insecticides meet the state’s standards for being registered for use in safflower. In our trials, we compared the new insecticides to plots in the field that had no insecticide treatment as well as plots treated with the local growers’ standard insecticide treatment.

The insecticides studied were cyclaniliprole (Harvanta 50 SL) in two trials from 2018-19 (Table 1) and acetamiprid (Assail 30 SG) in two trials both in 2020 (Table 2). In trials for both insecticides, the experimental plots were treated three times during the season following the grower’s standard retreatment intervals for their standard treatment. In some of the select data provided, you’ll see pest control patterns for lygus and beet leafhopper. We never observed enough stink bugs in any of the trials to make conclusions about how well these insecticides worked in safflower.

In the 2019 cyclaniliprole trial, we saw good efficacy against lygus nymphs, the juvenile stage of the insect. However, we didn’t observe obvious control with the new insecticide compared to the untreated control until two weeks after the second treatment and then throughout the evaluation period after the third treatment application (Fig. 2). The grower standard treatment during this same time performed better than the cyclaniliprole treatments in controlling lygus nymphs. We never observed any crop injury related to applications of the cyclaniliprole treatments. These observations together supported the registration of Harvanta 50 SL for use in safflower in California, meaning safflower growers can now use this product in the state.

In one of the 2020 acetamiprid trials, we saw good efficacy against beet leafhoppers. Control of beet leafhoppers was significantly better than the untreated control after each of the three treatments, but this usually lasted for only a week (Fig. 3). The acetamiprid performed similarly to or better than the grower standard control throughout the trial. We didn’t observe any crop injury effects from acetamiprid applications to safflower during the trial. These data are currently being evaluated for registration of Assail 30 SG in California to be used in safflower.

These new insecticides can provide valuable tools to safflower growers in California, not just for managing insect pests in safflower but also for managing pests that may migrate into neighboring cotton and tomato crops. The work done in these trials is supported by efforts put forward by local safflower growers and the pesticide manufacturers. The IR-4 project financially supports and coordinates the trials and product label registration efforts.

Figure 2. Three subsequent cyclaniliprole treatments effect on lygus nymphs. Nymph counts were the number of insects per sample, which was 50 sweeps using a net. Red vertical lines represent when the retreatments occurred. “DAT” means days after treatment.

The IR-4 Project
Since 1963, the IR-4 project continues to serve the specialty crop industry by increasing pest management solutions for growers while securing healthy food safe for consumption.

IR-4 specialty crops include fruits, nuts, herbs and vegetables recommended for a healthy diet as well as flowers, trees and shrubs that enhance our environment. It’s no mystery in today’s world consumers demand high-quality produce and plants. Managing harmful insects, weeds and diseases are difficult tasks for today’s growers given current pest populations, exotic and invasive species, resistance management, regulatory restrictions, residue mitigation, organic food production and many other challenges. Access to integrated pest management (IPM) tools are essential for food security and human health.

The mission of IR-4 is to facilitate regulatory approval of sustainable pest management technology for specialty crops and specialty uses to promote public well-being. The label is the law, and IR-4 works in label expansion for the safe, legal and effective use of biological and conventional pesticides. On a national level, IR-4 works with producers, growers, stakeholders, academics and extension agents to identify pest management needs and potential solutions.

IR-4 stands for Interregional Research Project #4; a bit of a mouthful, but a relic of it’s past. Label expansion can be quite cost-prohibitive, with registration fees today reaching the six- and seven-figure level at times. Prior to 1950, pest control options like those registered in large acreage crops (wheat, corn, soybean, etc.) were not available to specialty crop growers due to these costs. Furthermore, minor use patterns on major crops left a deficit to grower needs. This dilemma was coined the “Minor Use Problem.” In the late 1950s, State Agricultural Experiment Station (SAES) directors, university extension agents and USDA recognized the need to develop processes for registering pesticides for use on specialty crops and minor uses on major crops. As a result, in 1964, an Interregional Research Project #4 titled, ‘Evaluation of Current Data and Needed Research to Determine Tolerance Limits of Chemicals for Minor Uses on Agricultural Products,’ was created. Now, if registrants go through IR-4, registration fees are waived and the necessary research is funded, provided the request comes from the public (growers, academics) and the use fits into an IPM strategy.

Figure 3. Three subsequent acetamiprid treatments effect on beet leafhoppers. Leafhopper counts were the number of insects per sample, which was 50 sweeps using a net. Red vertical lines represent when the retreatments occurred. “DAT” means days after treatment.

Today, the IR-4 Project operates as a unique partnership between USDA (both the National Institute of Food and Agriculture (NIFA) and the Agricultural Research Service (ARS)), SAES, the EPA, the plant protection materials industry, commodity groups and growers. In recent years, additional partnerships formed with USDA-Foreign Agricultural Service supporting international specialty crop export activities, Animal Plant Health Inspection Service working on selected invasive species, the Department of Defense’s Deployed Warfighter Protection Program providing regulatory support for public health pesticides, and CDFA.

IR-4 is constantly evolving to meet the needs of producers and consumers by providing tools for IPM and collaborating in global harmonization of residue levels. The Integrated Solutions Program focuses on research areas like pest problems without solutions, resistance management, residue mitigation and organic food production. The Biopesticide Regulatory Support Program furthers the development and registration of biopesticides by providing regulatory assistance to public-sector scientists and small businesses navigating the EPA registration process. The Environmental Horticulture Program focuses on invasive species and pollinator protection. International efforts include harmonizing crop groups and maximum residue levels to reduce trade barriers for U.S. producers.

Research requires funding; therefore, IR-4 is funded by USDA-NIFA and CDFA and receives in-kind contributions from SAES, U.S. EPA, the crop protection industry, Canada and commodity associations.

Headquartered at North Carolina State University, IR-4 has regional facilities at University of Florida, University of Maryland Eastern Shore, Michigan State University and UC Davis. There are also liaisons in every state working with local growers to identify safe and effective solutions for pest management. IR-4 research takes place at many land grant universities and USDA-ARS facilities across the country.

If you would like to get involved, please contact Kari Arnold, based in UC Davis, at (530) 574-9181 or klarnold@ucdavis.edu.

My Career as a Certified Crop Advisor: A Retrospective

By
Jerome Pier | Ph.D., CCA, PCA; Senior Agronomist, QualiTech Agronomy; Past Chair, Western Region Certified Crop Advisors Board of Directors
-
0
Jerome Pier (left) co-authored the 10th edition of the Western Fertilizer Handbook, one of the many highlights of his career. Pier believes it is a CCA’s job to bring the knowledge to the table required to meet California’s nitrogen management needs.

I will never forget my introduction to the miracle of agriculture in California’s Central Valley. I interviewed for an agronomist position for Netafim Irrigation in Fresno in June 1995. I was finishing my USDA post-doctoral job at the University of Lincoln, Nebraska and was tired of researching corn and soybeans. After my interview, they suggested I take my rental car on a tour around the Valley. I first drove to the Westside and was amazed at the variety of crops being grown, such as cotton, melons, alfalfa, fruit and nut trees, tomatoes, winegrapes and many others I didn’t recognize. After lunch, I looked to the east and was drawn to the snow-covered Sierras. I drove up highway 168 to Shaver Lake, the source of irrigation water for many of the crops I saw earlier in the day. I couldn’t believe that someone would pay me to live and work in an agronomist’s dream world. I accepted Netafim’s offer without hesitation.

Now that I have decided to retire, I am looking back at how California agriculture has changed from my first visit, and I wonder what lies ahead.

Start of the Journey
My career has allowed me to travel to growers’ fields throughout California and the Western U.S. When I started work in 1995, cotton and alfalfa were being grown on 3.3 million acres with only 400,000 acres of almond, 650,000 acres of grape and 60,000 acres of pistachio. Almond yields averaged around 1,000 lb/acre and growers were grossing around $2,000/acre. Citrus acreage was dominated by oranges with only 8,000 acres of mandarins. Sweet cherries were mainly grown in northern California with a few orchards in Tulare County. Processing tomatoes were grown on over 300,000 acres, and average yields were around 33 tons/acre. There were no blueberries being grown in California. Winegrapes were all grown on AxR 1 rootstock and growers were pulling out vineyards infested with phylloxera and replanting with new, less susceptible rootstocks. Winegrape growers invested in drip irrigation systems when they replanted their vineyards. Most growers fertilized with nitrogen once or twice a season and little else. Crops were irrigated by flooding or sprinklers. A few growers were experimenting with using drip irrigation in orchards and were deciding if they could get by with just a single drip line or would require two lines. Some growers were experimenting with buried drip irrigation in field crops. Buried drip asparagus was an early success in Firebaugh. Finally, the CCA program was just getting started with only a few hundred in California.

I became a CCA in 2003 soon after I became the Central Valley division agronomist for Western Farm Service. The exams were in-person and given four times a year in a few locations. The CCA program was challenged by attracting new members. With most consultants obtaining their PCA license and taking tests to qualify for different pest and disease categories, studying for a new program focused on agronomy and plant health was daunting. However, advisors that spent the time to obtain a CCA certification added to their skillset and knowledge of the multiple crops grown in California. 

Nearly 30 years later, California agriculture has changed significantly. California crops are still highly diversified, and production values outrank the next largest state by an order of magnitude. Permanent crops now dominate the landscape, especially tree nuts like almond and pistachio, which respectively now cover 1.3 million acres and 460,000 bearing acres. Almond yields are more than double what they were in 1995, and many growers feel they must achieve 3,000 lb/acre yields to remain profitable. Cotton, now predominantly Pima, is grown on approximately 166,000 acres. Alfalfa grows on 500,000 acres, about half of the acres in 1995. Mandarin acres are 10 times what they were in 1995. Sweet cherries are now found in Kern County to capture the early market, and the Bing variety is being replaced by newer, earlier harvested varieties. Nearly all processing tomatoes are grown with buried drip irrigation and yields have more than doubled. There currently are over 7,000 acres of blueberries grown in California. The number of winegrape rootstocks are bewildering. Asparagus is being grown by one or two producers with acreage so low it is not reported. Drip irrigation predominates over nearly every acre of crops produced. Most growers are split applying liquid fertilizers through their drip systems. Fertilizer programs are based on balanced blends containing nearly all plant-essential nutrients, both macro and micro. Many growers claim to be applying much less nitrogen fertilizer and getting much higher yields than they did in the past due to the efficiency of application of microirrigation.

Jerome Pier (stage) was previously chair of Western Region Certified Crop Advisors Board of Directors and has been a mainstay at multiple consultant meetings over the years (photo by Kristin Platts.)

In 2012, The Harter Report was published at the request of the California legislature. The report performed a mass balance accounting of nitrogen in two watersheds that were vulnerable to nitrate pollution of groundwater, the Salinas Valley and Tulare Lake Basin. The report determined nitrogen fertilizer was being overapplied and unaccounted-for nitrogen could potentially end up in drinking water. This report eventually led to growers having to complete Irrigation and Nitrogen Management Plans (INMP) to examine how farming practices might impact groundwater quality. It was from this point forward the Western Region CCA program acquired new members at a rapid pace to become the largest regional program in the world. CCAs who took a course on nitrogen management were qualified to sign grower INMPs. The Western Region CCA program continues to maintain a strong membership while other regions in the U.S. are struggling. I have always felt being a CCA elevates a consultant to a higher level of service to their grower-customers. For California agriculture to continue to farm sustainably, a holistic approach is needed, and the CCA brings that expertise to the farm.

Future Challenges
As I look to the future of California agriculture, I see the biggest challenge being irrigation management. A great deal of attention is paid to how growers are applying fertilizer, but it is very difficult to encourage growers to improve their irrigation practices. I feel this challenge is due to growers receiving an invoice for their fertilizer but considering water to be their personal resource. It is quite challenging to understand water movement underground and how much water crops require to be fully productive. Many growers manage water based on hours of irrigation and do not consider the volume of irrigation being applied. Most crop advisors, I feel, are hesitant to comment if they see a grower’s irrigation practice is not appropriate for fear of liability. I feel the CCA program brings soil, water and nutrient management tools to bear on this complicated issue. Our strong and well-respected Western Region CCA program gives me hope that California will continue to sustainably produce a cornucopia of the world’s food and fiber for many years to come.

The Role of Precision Agriculture in Optimizing Orchard Water Management in California

By
Srinivasa Rao Peddinti | Postdoctoral Researcher, Dept. of Land, Air, and Water Resources, UC Davis
-
0
Figure 1. Eddy covariance flux tower equipped with key instruments. A net radiometer on the left for measuring radiation balance, a gas analyzer and sonic anemometer at the center for monitoring gas exchange and wind speed, and the new LI-710 ET sensor on the right for measuring evapotranspiration.

California’s orchards are an agricultural marvel, producing an incredible variety of fruit and nut crops that are enjoyed across the nation and around the world. From the sprawling almond and pistachio orchards of the Central Valley to citrus and stone fruits in coastal regions, growers rely on sustainable management of resources to maintain productivity. Among these resources, water stands as the most critical and increasingly scarce resource. With multi-year droughts, increasing water regulations and growing competition for water resources, the efficient use of water has become a cornerstone of sustainable orchard management.

In this context, precision agriculture offers a path forward. By employing advanced monitoring technologies and data-driven approaches, growers can achieve a level of irrigation management that was previously unimaginable. Precision agriculture enables growers to optimize water application by delivering the right quantity at the right time and in the right place where it is most needed. This targeted approach to irrigation not only improves water use efficiency but also enhances tree health, reduces costs and minimizes the environmental impact of agricultural operations.

Understanding Orchard Water Use with Advanced Tools
One of the key tools in precision agriculture is the eddy covariance system (Fig. 1). This advanced technology measures the exchange of water vapor and carbon dioxide between the orchard and the atmosphere. By providing real-time data on evapotranspiration (ET), the combined loss of water from the soil and plants, eddy covariance systems help growers understand exactly how much water their orchard is using at any given moment.

This information is crucial for designing irrigation schedules that align water delivery with the actual needs of the trees. Such a tool is particularly valuable in large orchards, where water requirements can vary significantly across the field due to differences in soil type, tree age or microclimatic conditions. Previously, eddy covariance systems were too expensive and complicated to be integrated in commercial irrigation applications. However, recently, the new ET sensor, LI-710 (shown on the right in Fig. 1), has become available, providing similar data and functionality for growers at a lower cost compared to the traditional eddy covariance systems.

Monitoring Tree and Soil Water Status for Optimal Irrigation
Complementing the eddy covariance system are ground-based monitoring tools like sap flow sensors and soil moisture sensors (Fig. 2). Sap flow sensors are installed directly on the tree trunks to measure the movement of water through the xylem, providing a direct indication of how much water the tree is using. Meanwhile, soil moisture sensors (Fig. 2) measure the volumetric water content of the soil, providing information about the amount of water stored in the soil. In contrast, soil water potential sensors measure the energy which water is being held in the soil, offering insights into the availability of water for plant uptake. Both types of sensors are valuable for optimum irrigation management.

Together, these tools give growers a detailed picture of the water status in their orchards, from the soil to the trees and into the atmosphere. For example, soil water potential sensors can indicate when the soil is too dry for tree roots to extract water, signaling the need for irrigation. Conversely, sap flow measurements can help growers avoid over-irrigation, which not only wastes water but can also lead to problems like nutrient leaching and waterlogging of the root zone.

Comparing Irrigation Strategies for Better Decision-Making
The benefits of precision irrigation become especially clear when evaluating various irrigation strategies. Figure 3 presents the comparative outcomes of two irrigation methods: full irrigation and deficit irrigation.

In the full irrigation treatment, trees received enough water to meet their entire evapotranspiration demand, ensuring optimal growth conditions. Soil moisture levels in this treatment remained stable throughout the season, with trees maintaining high transpiration rates and minimal water stress. This approach is ideal for maximizing productivity, but it also requires a significant amount of water, which may not be sustainable during drought years or under strict water allocation limits required under the Sustainable Groundwater Management Act in some regions of California.

In contrast, the deficit irrigation treatment deliberately imposed mild water stress on the trees by providing less water than their full evapotranspiration demand. This strategy resulted in lower soil moisture levels and reduced transpiration rates. However, the trees were still able to maintain reasonable productivity levels, demonstrating deficit irrigation can be a viable strategy for conserving water without sacrificing too much yield.

The choice between these two approaches depends on growers’ specific circumstances, including water availability, crop type and economic considerations. For many growers in the Central Valley, deficit irrigation offers a practical way to reduce water use while maintaining orchard productivity during challenging conditions such as multi-year droughts.

Figure 2. Installation of soil moisture sensors, soil water potential sensors and sap flow sensors in a pistachio orchard near Madera, Calif. The sap flow sensors are attached to the tree trunks and covered with aluminum foil while the soil sensors are installed below ground at depths of 30 cm and 60 cm. Data collection was managed using a data logger with power supplied by a battery connected to a solar panel.

Adapting Irrigation Practices to Orchard Conditions
In practice, implementing precision irrigation requires more than just installing sensors and collecting data. It requires incorporating this information into a comprehensive management plan customized to the specific conditions and needs of each orchard. Trees in sandy soils, for example, may require more frequent but smaller irrigation events, while those in clay soils may benefit from less frequent but deeper water applications. In a similar manner, young trees with limited root systems often have water requirements that differ from those of fully grown trees.
Precision agriculture tools can help growers account for these differences and tailor their irrigation practices to meet the specific needs of their orchards. By combining real-time data with an understanding of soil and tree dynamics, growers can create irrigation schedules that maximize water use efficiency and optimize tree health.

Economic and Environmental Benefits of Precision Irrigation
The economic benefits of precision irrigation are significant. Efficient water usage allows growers to lower both their water expenses and the energy costs linked to pumping. In addition, healthier trees that receive the right amount of water are more productive and less susceptible to diseases, resulting in higher yields and better-quality fruit or nuts. These advantages can help compensate for the upfront costs of precision agriculture technologies, making them a valuable long-term solution for growers.

Beyond the economic benefits, precision irrigation also has important environmental implications. By reducing overirrigation, growers can minimize the risk of nutrient leaching, which occurs when excess water carries fertilizers beyond the root zone and into groundwater or surface water bodies. This not only helps protect water quality but also reduces the need for additional fertilizer applications, saving both money and resources. Furthermore, by conserving water, growers can reduce their overall water footprint, contributing to the sustainability of California’s agricultural sector.

Figure 3. Comparison of soil moisture content, soil water potential and transpiration efficiency (T/ET) under full irrigation (top) and deficit irrigation (bottom) treatments in a pistachio orchard near Woodland, Calif. Volumetric water content (VWC) and soil water potential (SWP) are displayed for 30- and 60-cm depths along with transpiration efficiency data from two field treatments (FT1 and FT2 for full irrigation, DT1 and DT2 for deficit irrigation) (Peddinti and Kisekka 2025).

Overcoming Challenges and Looking Ahead
The adoption of precision agriculture is not without its challenges. For many growers, the upfront cost of purchasing and installing advanced monitoring equipment can be a barrier. Furthermore, understanding and utilizing the data generated by these tools often involves a learning curve, as growers adapt it to their daily management practices. However, as more growers adopt these technologies and share their experiences, the knowledge base around precision irrigation continues to grow, making it easier for others to follow suit.

Educational initiatives and outreach programs are essential for encouraging the adoption of precision agriculture practices. Workshops, field days and demonstration projects can help growers see these technologies in action and understand their potential benefits. Collaborations between researchers, industry stakeholders and growers are essential for developing practical solutions that address the real-world challenges faced by California’s orchard managers.

Precision Agriculture as a Long-Term Solution
Looking to the future, precision agriculture is likely to become even more sophisticated with the integration of artificial intelligence, machine learning and advanced data analytics. Predictive models that use data from eddy covariance systems, sap flow sensors and soil moisture probes could provide growers with real-time recommendations for irrigation scheduling, taking the guesswork out of water management. Similarly, remote sensing technologies, such as drones and satellite imagery, could complement ground-based monitoring tools by providing a broader perspective on orchard health and water use.

As these technologies continue to evolve, they will play an increasingly important role in helping California’s growers navigate the challenges of water scarcity and climate change. By embracing precision agriculture, orchard managers can ensure the long-term sustainability of their operations while maintaining California’s position as a global leader in fruit and nut production.

References
Peddinti, S. R., Gordon, P., Oker, T., Marino, G., and Kisekka, I., 2025. Evaluating transpiration efficiency and soil moisture dynamics under varying irrigation regimes. Under preparation.

Soil Disinfestation with Steam in Vegetable Crops

By
Steve Fennimore | CE Specialist, Professor, UC Davis
-
0
Figure 2. Commercial scale steam applicator. Here, steam is injected into the bedtop in bands aligned with where the seedlines will be placed.

Increasing demand for organic produce and lack of herbicides for this crop sector has resulted in high weeding costs for many vegetable crops. Organic fields tend to be weedier than conventional fields because organic crops have fewer weed control tools. Lack of residual herbicides for organic crops means a missed cultivation or hand weeding pass often results in weeds escaping and producing weed seed, making the problem worse. Most conventional crops have residual herbicides that provide some protection against weed escapes, such as during wet conditions when it is not possible to cultivate or hand weed. Organic crops lack the protection residual herbicides provide.

Increasing labor costs and labor shortages mean hand weeding costs continue to climb, and laborers may not be available when needed. Loss of Dacthal has eliminated a key weed control tool for vegetables, and new options are needed. It is unlikely new herbicides will replace old products like Dacthal that are lost to small markets like vegetable crops. More recent technologies, such as the new intra-row intelligent cultivators and laser weeders, help reduce the number of weeds that must be removed by hand, but they do not eliminate the need for hand weeding.

Few methods are available for organic crops to achieve residual control of weeds. Possible methods are soil solarization and steam. Both methods kill weed seed in the shallow seedbank using thermal heat to kill weeds. Here, we will discuss the use of steam for residual weed control.

How Does Steam Work?
Water heated above 212 degrees F becomes steam. Steam injected into soil transfers the heat from the steam to the soil particles, heating them and killing nearby pathogens and weed seed. Steam condenses onto the cooler soil particles, releasing its heat as it returns to the water phase. Once vaporized, steam can be heated to higher temperatures, becoming “dry steam.” The advantage of dry steam is it disperses further into the soil, transferring the heat energy to a larger volume of soil than would be the case with a cooler “saturated steam,” which holds a lot of water droplets. Target temperatures of the soil will range between 150 degrees F to 180 degrees F. The objective is pasteurization, not sterilization. Maintaining temperatures in this moderate “Goldilocks” range will control most pathogens and weed seed while not damaging beneficial soil microbes.

Figure 1. Band steam injected into the seedline then later seeded with carrots. The carrots grow in a band that is virtually weed-free, while weeds survive outside the band can be readily removed by conventional cultivation tools (all photos by S. Fennimore.)

Benefits of Steam
Steam injected into soils controls both weed seed and soilborne pathogens. Guerra et al. (2022) found field steaming reduced weed emergence and subsequently improved hand weeding efficiency. The residual effect of steam on weeds is because it kills weed seed in the steam-treated zone, thus reducing weed emergence.  Furthermore, Guerra et al. (2022) found steam controls pathogens, such as Pythium spp. and Sclerotinia minor. Additionally, Lu et al. (2009) reported a 90% reduction in Fusarium oxysporum with steam treatments at 158 degrees F or higher. In regions like Monterey County, where Fusarium oxysporum f. sp. lactucae severely affects lettuce production and Pythium ultimum threatens leafy greens, addressing these diseases is critical (Martin and Loper 1999).
Interest in sustainable practices like steam disinfestation has grown due to rising labor costs and regulatory pressures on fumigants. Originating in the 1880s, steam disinfestation effectively controls weeds and eliminates soilborne pathogens (Baker 1962). The earliest approach, broadcast sheet steaming, involved applying steam to the entire soil profile, but this method consumed excessive energy and had limited efficiency (Gay et al. 2010a). Band steaming, which injects steam into narrow seedline bands prior to seeding, offers higher efficacy with reduced resource input (Guerra et al. 2022) (Fig. 1). This method effectively addresses persistent weed and pathogen control issues (Guerra et al. 2022; Gullino 2022; Fennimore et al. 2014). The thermal energy kills weed seeds and pathogen propagules at soil temperatures above 70 degrees C (Baker 1962).

Band steaming effectively reduces soilborne pathogens such as Pythium spp. and Fusarium spp. (Guerra et al. 2022; Kim 2021; Fennimore 2014). Due to their significant environmental and health impacts, chemical controls for soilborne diseases, such as methyl bromide, were phased out in 2005 (Fennimore et al. 2008). In the Salinas Valley, Fusarium spp. and Pythium spp. are prevalent, affecting key crops like strawberries and lettuce. Recent studies with steam in the Salinas Valley found steam reduced incidence of lettuce drop, fusarium wilt, verticillium wilt and weeds in lettuce (Table 1; Fennimore unpublished). 

Where Does It Fit and How Much Does It Cost?
Steam is most appropriate for high-value vegetable crops, such as organic carrots, lettuce and spinach, where weed control costs are high. High-density crops, such as carrots, spinach and spring mix lettuce, are grown at high densities, making it difficult to cultivate or hand weed. It may be possible to precisely apply steam to these crops at a cost that is less than the cost of labor. That is the objective of our work with steam. Weed seed in the soil killed by steam do not emerge, and therefore steam is a prophylactic treatment in advance of the pest. This contrasts with intelligent cultivators and laser weeders, which control weeds after they emerge. It is possible that preplant steam application followed by intelligent weeding technologies could remove the need for hand weeding completely.

We have often observed more than a 90% reduction in hand weeding of steam treated plots compared to a no steam treated plots. For Pythium spp. where steam is applied 6 inches deep, this pathogen is reduced by 99%. Similar results have been obtained for Verticillium wilt and lettuce drop. Fusarium is more difficult to control, and higher temperatures (190 degrees F) are needed to control this pest.

We tested a custom-built steam applicator for vegetable crops in 2024 (Fig. 2). The machine injects dry steam into bands aligned with where the crop will be seeded in a subsequent operation.

We are currently working with partners to commercialize this process. Reductions in hand weeding of 90% (Table 1) could reduce hand weeding costs by $200 per acre. The reductions in Fusarium infection could mean the difference between a net income of $4,550 with no steam compared to a net income of $17,500 in iceberg lettuce, meaning the value of steam treatment could be worth $12,950 per acre.

Beneficials
Our findings suggest although band steaming initially disrupts the soil microbiome, significant recovery occurs within 30 days, supporting its potential to preserve long-term soil health while suppressing soil pests. The novelty of band steaming lies in its precision, targeting soils only where needed in the seedline where crops will be planted. This focused approach minimizes the overall impact on the soil, allowing unaffected areas to support microbiome recovery. This research reinforces the viability of band steaming as a sustainable and environmentally friendly alternative for pest control in agriculture, while maintaining soil biodiversity and functionality.

Band steaming for field grown vegetable crops provides a much-needed new tool for weed and pathogen control for vegetable crops. The process controls several key diseases and weeds, without damage to soil health. Work is currently underway to commercialize band steaming and to reduce cost of application.

Table 1. Diseased plant counts and weed densities (1000s/A) as well as hand weeding times.

References
Baker, K.F. 1962. Principles of heat treatment of soils and planting material. J. Aust. Inst. Agric. Sci. 28:118-126.

Fennimore, S.A., F.N. Martin, T.C. Miller, J.C. Broome, N. Dorn, and I. Greene. 2014. Evaluation of a mobile steam applicator for soil disinfestation in California strawberry. HortScience 49(12):1542-1549. https://doi.org/10.21273/HORTSCI.49.12.1542.

Gay, P., P. Piccarolo, D. Ricauda Aimonino, and C. Tortia. 2010a. A high efficiency steam soil disinfestation system, part I: Physical background and steam supply optimization. Biosystems Eng. 107:74-85.

Gay, P., P. Piccarolo, D. Ricauda Aimonino, and C. Tortia. 2010b. A high efficacy steam soil disinfestation system, part II: Design and testing. Biosystems Eng. 107:194-201

Guerra, N., S.A. Fennimore, M.C. Siemens, and R.E. Goodhue. 2022. Band steaming for weed and disease control in leafy greens and carrots. HortScience 57:1453-1459. https://doi.org/10.21273/HORTSCI16728-22.

Kim, D.S., S. Kim, and S.A. Fennimore. 2021. Evaluation of broadcast steam application with mustard seed meal in fruiting strawberry. HortScience 56:500-505. https://doi.org/10.21273/HORTSCI15669-20.

Martin, F.N., and J.E. Loper. 1999. Soilborne plant diseases caused by Pythium spp.: Ecology, epidemiology, and prospects for biological control. Crit. Rev. Plant Sci. 18:111-181. https://doi.org/10.1080/07352689991309216.

Lu, P., D. Ricauda Aimonino, G. Gilardi, M.L. Gullino, and A. Garibaldi. 2010. Efficacy of different steam distribution systems against five soilborne pathogens under controlled laboratory conditions. Phytoparasitica 38(2):175-189. https://doi.org/10.1007/s12600-010-0086-8.

2024 CCA of the Year Winner: UCCE Advisor Franz Niederholzer Earns the Award at This Year’s Crop Consultant Conference

By
Taylor Chalstrom | Editor
-
0
This year’s CCA of the Year winner was Franz Niederholzer, UCCE farm advisor in Colusa and Sutter/Yuba counties and previous member of the WRCCA Boad of Directors from 2006 to 2022 (all photos by Kristin Platts.)

The 2024 Crop Consultant Conference, hosted on September 25 and 26 in Visalia, Calif. in a collaborative effort by JCS Marketing Inc. and Western Region Certified Crop Advisers (WRCCA), offered its highest numbers of continuing education yet and provided the opportunity for consultants, industry suppliers, researchers and others to network and learn.

In addition to CCAs, PCAs and growers receiving much-needed continuing education credits during the Conference’s established dual education track, WRCCA also presented its fifth-annual Crop Consultant of the Year award and Allan Romander Scholarship and Mentor Awards.

Stephen Vasquez, executive director at Administrative Committee for Pistachios and WRCCA Board Chair, presented the awards.

CCAs, PCAs, growers and industry professionals congregated during breakfast, lunch and on the tradeshow floor in mornings and afternoons.

CCA of the Year
The CCA of the Year award recognizes a CCA in the western region (North Valley, South Valley, Coast and Desert) of the U.S. who has shown dedicated and exceptional performance as an advisor. The ideal candidate leads others to promote agricultural practices that benefit the farmers and environment in the western region. Selection criteria includes a peer nomination process, a scope of the CCA work, special skills and abilities, professional involvement and mentorship and community involvement.

This year’s CCA of the Year winner was Franz Niederholzer, UCCE farm advisor in Colusa and Sutter/Yuba counties since 2002. Niederholzer is a UC Davis graduate in soil science and studies orchard mineral nutrition, rootstock evaluation, crop load management and airblast spray coverage and drift within UCCE and Nickels Soil Lab. Additionally, Franz was a member of the WRCCA Boad of Directors from 2006 to 2022. While on the Board, he served on the WRCCA Testing and Continuing Education Committee, including 10 years as committee chair.

Niederholzer shared some words about the importance of the CCA program.

“It’s a great honor to have been part of the Board, to have interacted with a number of really terrific individuals and to receive this as a surprise and a great honor because of the program,” he said. “There’s so much talent, decades of experience available to help agriculture and horticulture in general, not just ag, but anything that’s green that’s grown.”

Attendees had access to 10.5 DPR hours and 13 CCA hours as well as CDFA FREP, Arizona PCA and Nevada PCA hours.

Mentor Awards
The mentor honorariums award $500 to an agriculture educator who is training and mentoring the next group of consultants, growers and industry professionals.

Sangeeta Bansal, assistant professor of soil health in the Jordan College of Agricultural Sciences and Technology at California State University, Fresno; Lindsay Hofsteen, associate professor of plant science/viticulture at San Joaquin Delta College; Michael Kanyi, associate professor of agricultural education and environmental science at Imperial Valley College; and Nathan Dickens, adjunct professor of plant science at Los Angeles Pierce College were this year’s mentor award recipients.

Bansal plans to use the funds to order supplies, soil testing kits and purchase consumables to set up small-scale crop nutrition and soil health projects. Hofsteen plans to purchase lab supplies and updated materials for her plant science class and pruning tools for her viticulture class. Kanyi plans to acquire instructional resources for hands-on learning, specifically gardening tools and a hydroponic system. Dickens plans to use the funds to teach major agronomic challenges through the development of a community-type demonstration garden.

An educational panel on potassium applications and timing in perennial crops caught the attention of attendees at this year’s Crop Consultant Conference.
Honorarium winners Sangeeta Bansal (far left) and Lindsay Hofsteen (far right), scholarship winners Olivia Bruns (middle left) and Sawyer Claussen (middle right), and CCA of the Year winner Franz Niederholzer (middle) with their awards at the 2024 Crop Consultant Conference in Visalia, Calif. in September.

Scholarship Awards
Tri-Tech Ag Products’ Eryn Wingate, CCA and Board treasurer, presented the $1000 scholarship awards to four deserving students.

“This is my favorite part of this conference, where we get to acknowledge these promising students and try to help support you in your path to becoming a certified crop advisor,” Wingate said.

Olivia Bruns of Woodland, Calif.; Sawyer Claussen of La Selva Beach, Calif.; Jack Gonzalez of Bakersfield, Calif.; and Osvaldo Acuña of Mesa, Ariz. were this year’s scholarship award recipients. All had excellent track records of awards, leadership and community service as well as internship experience. They were each nominated in the North Valley, South Valley, Coastal and Desert regions, respectively.

Bruns plans to become a CCA and PCA while finishing her bachelor’s degree in plant sciences. Claussen plans to become a CCA next year and finish his bachelor’s degree in plant sciences. Gonzalez plans to finish his bachelor’s degree in plant sciences and accumulate work experience during the next few summers before taking the CCA exam. Acuña plans to become a CCA and PCA at the same time he earns his bachelor’s degree in agricultural technology management and sustainable plant systems.

The recipients of this year’s scholarship and mentor awards play a vital role in the development of CCAs in the western region and will continue to educate growers and prospective CCAs in the future.

On behalf of the JCS Marketing Inc. team and Progressive Crop Consultant magazine, the editor would like to thank all that attended this year’s Crop Consultant Conference in Visalia. The conference was a success with a record amount of continuing education and over 600 attendees that enjoyed the valuable seminars, exhibitors, networking and food.

Developing New Technologies to Monitor Virus-Infected Vines in the Vineyard

By
Eve Laroche-Pinel | Postdoctoral Researcher, Computational Agriculture, California State University, Fresno, Monica Cooper | UCCE Viticulture Farm Advisor, Napa County, Marc Fuchs | Dept. of Plant Pathology and Plant-Microbe Biology, Cornell University and Luca Brillante | Assistant Professor of Viticulture, Dept. of Viticulture and Enology, California State University, Fresno
-
0

In viticulture, grapevines face many threats, with virus diseases standing out as insidious adversaries. Among these, leafroll and red blotch pose significant challenges due to their elusive nature and lack of curative solutions. Traditional containment methods involve the laborious and costly process of identifying infected vines and replacing them with healthy ones (i.e., roguing). Identifying virus-infected grapevines is no simple task. It requires the expertise of individuals well-versed in the nuances of virus symptoms. Even for professionals, accurate diagnosis often necessitates sampling vine tissue for laboratory analysis, typically through molecular testing such as Polymerase Chain Reaction (PCR). This process is time-consuming and financially burdensome, underscoring the urgent need for innovative solutions to streamline detection efforts. Recent advancements in technology offer a glimmer of hope, promising more efficient and precise methods of detection and management.

Vineyard management has seen a surge in precision tools to optimize cultivation practices. Central to this trend is the development of sensors capable of delving deeper into the vine’s spectral response to stress. These advanced technologies empower growers to monitor vine health with unprecedented precision, offering insights that were once inaccessible through conventional means. In 2019, a groundbreaking project was launched at California State University, Fresno, funded by USDA, CDFA, CSU-ARI and F3, Fresno-Merced Future of Food innovative initiative, and in collaboration with experts from Cornell University and UC ANR. The initiative aimed to revolutionize the detection of leafroll and red blotch viruses using hyperspectral imagery.

The hyperspectral imaging project was project was launched at California State University, Fresno, funded by USDA, CDFA, CSU-ARI and F3, Fresno-Merced Future of Food innovative initiative, and in collaboration with experts from Cornell University and UC ANR (all photos courtesy L. Brillante.)

Hyperspectral Imagery

At its core, hyperspectral imaging is a cutting-edge technology that enables measuring an object’s response to light absorption across a wide range of wavelengths. By analyzing the spectral signature of grapevines, researchers can glean valuable insights into their physiological and health state. For instance, variations in chlorophyll and anthocyanin concentrations manifest as distinct patterns in the visible spectrum (the portion of light wavelengths we interact with our eyes), while changes in cell structure influence near-infrared wavelengths (which are not visible to our eyes). Furthermore, water content and other chemical compounds (cellulose, sugar) leave their imprint in the shortwave infrared domain. Crucially, diseases such as leafroll and red blotch can alter these spectral signatures, offering non-invasive means of detection.

The project’s first phase involved sampling 500 leaves from both healthy and virus-infected plants (by leafroll, red blotch or both viruses). These leaves were then subjected to hyperspectral imaging within the controlled environment of a dark cabinet in the laboratory, capturing images across the 500- to 700-nm range. Machine-vision techniques, particularly Convolutional Neural Networks (CNN), were employed to analyze hyperspectral imagery and detect signs of infection in grapevines. CNNs are a type of deep learning algorithm that excels at image recognition tasks by automatically learning features from raw pixel data. During this phase, the CNN model achieved impressive results. For binary classification, distinguishing between infected vines (with red blotch or leafroll) and healthy ones, the model attained an accuracy of 87% when symptoms were visible at post-veraison and 85.6% when symptoms were not yet visible to the naked eye, thus at pre-veraison. This demonstrated the model’s effectiveness in detecting infections even before visible symptoms manifested. Furthermore, in a more complex multiclass classification task aimed at identifying the specific virus infecting the vine, thus distinguishing between leafroll and red blotch, the CNN model achieved an overall accuracy of 76.9%. This highlights the model’s ability to differentiate between viruses based on subtle spectral variations (Sawyer et al. 2023).

Buoyed by these promising outcomes, the project advanced to its second phase, transitioning from the controlled environment of the lab to the dynamic conditions of the field. Utilizing the same hyperspectral camera, images of the side of 700 vines were captured in the vineyard, focusing specifically on detecting red blotch virus. When symptoms were not visibly apparent, a model achieved an overall accuracy of 68.6%. As the season progressed and symptoms became more pronounced, the accuracy improved significantly, reaching 76.6% with a Support-Vector Machine (SVM) model. This underscores the model’s adaptability to real-world conditions and its efficacy in detecting infections even in the absence of visible symptoms (Laroche-Pinel et al. 2024a).

One phase of the project involved deploying a drone-mounted hyperspectral camera to capture images of ~300 vines during the post-veraison stage. This aerial perspective provided a comprehensive view of the vineyard, enabling it to assess vine health and identify infections across a potentially larger scale.

In the third phase of the project, the approach was elevated by deploying a drone-mounted hyperspectral camera to capture images of ~300 vines during the post-veraison stage. This aerial perspective provided a comprehensive view of the vineyard, enabling it to assess vine health and identify infections across a potentially larger scale. Expanding beyond mere detection, the focus shifted toward leveraging the spectral response of the vines to extract valuable biochemical information. Specifically, a model was used to predict the concentrations of three key pigments (chlorophyll, carotenoids and anthocyanins) based on the spectral data captured by the drone. The striking results revealed significant differences in pigment concentrations between infected and non-infected vines. Non-infected vines exhibited higher predicted levels of chlorophyll and carotenoids, indicative of healthier foliage and photosynthetic activity. Conversely, infected vines displayed elevated levels of anthocyanins, a response often triggered by stressors such as viral infections. Utilizing the spectral information, machine learning techniques were applied to classify vines as either infected or non-infected by red blotch. The model achieved an impressive accuracy rate of 87% in binary classification, further underscoring the efficacy of hyperspectral imaging coupled with advanced data analysis in disease detection and management (Laroche-Pinel et al. 2024b).

Table 1. Machine learning model accuracy and hyperspectral imaging efficacy. The results highlight the model’s ability to differentiate between viruses based on subtle spectral variations and adaptability to real-world conditions and its efficacy in detecting infections even in the absence of visible symptoms.

Pivotal Advancement in Vineyard Monitoring

This phase represents a pivotal advancement in vineyard monitoring, offering a holistic approach that transcends the mere identification of infections. By harnessing the spectral signatures of grapevines, growers gain valuable insights into their physiological status and biochemical composition, empowering them to make informed decisions regarding vineyard management practices. The project’s third phase marks a significant milestone in the quest for more effective vineyard management strategies. Overall, these findings represent a significant leap forward in vineyard management. As the battle against grapevine virus diseases rages on, the integration of hyperspectral imaging holds immense promise for vineyard management. By harnessing the power of advanced technology, growers can detect and mitigate threats more effectively, safeguarding the health and productivity of their vineyards. With ongoing research and innovation, the vision of a future where precision tools enable proactive disease management is within reach.

References
Laroche-Pinel, E., Singh, K., Flasco, M., Cooper, M.L., Fuchs, M., Brillante, L. (2024a). Grapevine Red Blotch Virus Detection in the Vineyard: Leveraging Machine Learning with VIS/NIR Hyperspectral Images. (In review)

Laroche-Pinel, E., Singh, K., M., Cooper, M.L., Fuchs, M., Brillante, L. (2024b). Advanced Detection of Grapevine Red Blotch Virus at the Plant Level in Vineyards: A Drone-Based Approach using VIS/NIR Hyperspectral Camera, Machine Learning, and PROSPECT Inversion Model. (In Prep)

Sawyer E., Laroche-Pinel E., Flasco M., Cooper M.L., Corrales B., Fuchs M., Brillante, L. (2023) Phenotyping grapevine red blotch virus and grapevine leafroll associated viruses before and after symptom expression through machine-learning analysis of hyperspectral images. Frontiers in Plant Science. 14:1117869. doi: 10.3389/fpls.2023.1117869

Olive Yields Benefit from a New Strategy Using Naphthaleneacetic Acid to Manage Crop Load

By
Elizabeth Fichtner | Ph.D., UCCE Farm Advisor, Tulare County and Carol J. Lovatt | Professor of Plant Physiology, Emeritus, Dept. of Botany and Plant Science, UC Riverside
-
0
Figure 1. Application of naphthaleneacetic acid at full bloom to one side of the tree eliminates fruit set on the treated surface, allowing for fruit development on the untreated side of the canopy (photos courtesy E. Fichtner.)

The alternate bearing (AB) nature of olive is one of the top physiologically driven challenges faced by olive growers. AB refers to the tree’s habit of producing a heavy crop in one year followed by a light crop the next year. The heavy crop is referred to as the ‘on’ crop, which is characterized by large yields with small fruit that may mature late and have reduced commercial value due to size. Conversely, the ‘off’ crop has characteristically low yields with large fruit that may not be cost-effective to harvest. AB adversely affects the consistency of the fruit supply, thus having a negative economic impact on every step within the production chain from farm to consumer. Because mitigation of AB can best be achieved by management of crop load, UC researchers have conducted recent studies evaluating the efficacy of a new chemical flower thinning strategy using naphthaleneacetic acid (NAA) (Fig. 1) applied at full bloom to only one side of the tree annually or biennially to reduce the severity of AB and maintain higher annual yields of commercially valuable size fruit.

Mechanisms of Alternate Bearing
There are currently four known mechanisms by which the on crop reduces flowering and fruit number to contribute to AB of ‘Manzanillo’ table olive orchards. The first mechanism of AB is the suppression of summer vegetative shoot growth by the current crop (Fig. 1). Flowers and fruit on olive are borne on one-year-old shoots; consequently, the vegetative growth in the current year provides the nodes at which inflorescences form in the subsequent spring. Research studies conducted in Tulare County have demonstrated the fruit’s suppression of vegetative growth is irreversible after pit hardening. As a result, crop management strategies designed to reduce the current season’s crop must be implemented by June to promote summer vegetative growth and increase return bloom the following year. The second mechanism of AB is inhibition of floral development (typically initiated in July) by the current season’s crop. The third mechanism of AB is the inhibition of spring bud break. As a result of bud break inhibition, even floral buds that have formed may not open at bloom. Last, the current season’s crop causes the abscission of floral buds. Since the off crop has an effect opposite to that of the on crop, once AB is initiated in an olive tree, cycles of on and off floral intensity and cropping are perpetuated by the opposing effects of high and low crop loads on these mechanisms.

Figure 2. Eliminating crop on one side of the tree promotes extensive vegetative growth (A). Fruit is then borne on the untreated side of the tree (B) in the current season. The non-bearing side of the tree (A) will support the formation of flower buds that will give rise to inflorescences the following year.

Naphthaleneacetic Acid as a Solution
Historically, olive growers have used NAA, a plant growth regulator, as a fruit thinning agent to reduce the current season’s fruit load. Upon application, NAA is absorbed by leaves and developing fruit and is translocated to the peduncle where it incites an abscission layer at the point of attachment to the stem. As an olive fruit thinning agent, NAA is typically applied 12 to 18 days after full bloom (i.e., during fruit set). Treatments are made with an NAA ammonium salt product, such as Liqui-Stik Concentrate (Loveland Products) applied as a dilute spray (300 to 500 gallons per acre). Chemical thinning with NAA can be risky; too early an application may result in overthinning, whereas too late an application may not thin sufficiently. Additionally, hot temperatures (>100 degrees F) within one week of application may enhance the efficacy of NAA, resulting in excess thinning. Due to the greater risk of spring heat waves in the south, chemical thinning has been more commonly utilized by table olive growers in the Sacramento Valley than in the southern San Joaquin Valley.

With support from the California Olive Committee, researchers have been evaluating the use of NAA at full bloom (rather than 12 to 18 days after bloom) as a crop management tool to reduce the severity of AB, which is measured as alternate bearing index (ABI) on a scale from 0 (no AB) to 1 (total AB, crop one year, no crop the other year). These studies tested a full bloom NAA application to one side of the tree with the goal of eliminating crop on one side of the canopy (Fig. 2) while maintaining crop on the opposite side. Annual and biennial applications of NAA to just one side of the tree were compared. To implement the annual NAA application strategy in a commercial orchard, growers would apply NAA to one side of the tree at full bloom in year 1, then on the other side of the tree in year 2. In the biennial strategy for NAA application, there would be a year of rest (no treatment) between the application to one side of the tree in year 1 and the other side in year 3.

After 4 years of research, NAA application either annually or biennially at full bloom did not affect cumulative total yield. However, full bloom NAA applications to one side of the tree significantly reduced the severity of AB from near total AB (ABI = 0.94) for the untreated on/off control trees by 20% when applied annually and 38% when applied biennially. The results indicate annual total yields were more uniform from year to year, especially for trees treated biennially, which improves the economics of all steps in the production chain from farm to consumer.

In addition, both annual and biennial applications of NAA to one side of the tree at full bloom had positive effects on the yield of commercially valuable size (CVS) fruit (medium plus large) compared to the untreated on/off control trees. Biennial NAA application at full bloom reduced the ABI for CVS fruit 43% compared to the untreated control trees, whereas annual NAA application at full bloom only reduced the ABI for CVS by 12.5%. Importantly, application of NAA at full bloom to one side of the tree biennially resulted in 40% greater cumulative yields of medium plus large fruit than untreated control trees, with annual treatment increasing yield of medium plus large fruit only 20%. The increased and more uniform yields of CVS fruit resulting from biennial NAA application at full bloom to one side of the tree provide growers with greater, more reliable annual income. Moreover, a biennial application of NAA (once every other year) is half the cost of an annual NAA application. Since NAA is applied to only one side of the tree at full bloom, for which total removal of the crop is desired, the risk of overthinning with NAA is eliminated in this strategy compared to the standard practice of applying NAA to the whole tree during fruit set. Whereas a grower must decide to treat once every other year based on floral intensity and without knowledge of the year’s fruit set, the fact that only one side of the tree is treated lessens the effect of a subsequent poor set. The NAA standard practice provides the grower a window of 12 to 18 days after full bloom to evaluate fruit set when deciding to treat. If the grower sprays NAA according to the standard practice and set is subsequently negatively impacted (potentially by even NAA itself interacting with high temperatures), the whole tree will be affected.

The results of this research demonstrate the potential value of NAA applied at full bloom to shift the crop load to one side of the tree and then the other side biennially. This technique essentially creates a bearing and non-bearing side to each tree, allowing for unsuppressed vegetative growth on the treated side and documents the need for a rest period with no NAA application until year 3 to allow the tree to fully recover. Biennial application of NAA at full bloom to one side of ‘Manzanillo’ olive trees successfully reduced the severity of AB and increased yields of commercially valuable size olive fruit better than annual application of NAA or the untreated on/off control trees. The use of NAA at bloom to mitigate AB warrants further investigation. Researchers are also actively investigating the use of pruning 28 days after full bloom to only one side of the tree annually or biennially as a means of mitigating AB to achieve consistent yields of commercially valuable size fruit.

123...37Page 1 of 37
-Advertisement-



EDITOR PICKS

POPULAR POSTS

POPULAR CATEGORY

©