Home Blog Page 2

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.

Are Nematodes a Problem in Pistachio?

By
Andreas Westphal | Dept. of Nematology, UC Riverside
-
0
Pistachio rootstock UCB1 D90 in May of the third growing season in microplots with sand. On left, no root lesion nematodes. On right, many root lesion nematodes.

Pistachio has enjoyed decades of limited reported damage from plant-parasitic nematodes. This contrasts with other tree nut crops as almond and walnut. While almond and stone fruits were long encumbered by root-knot nematodes, these crops have benefitted from protection against these culprits by the introduction of peach rootstock ‘Nemaguard.’ This fascinating rootstock carries sustainable resistance since the 1960s. Only more recently has the detection of the peach root-knot nematode (PRKN) illustrated the vulnerability of this and other rootstocks with resistance to southern root-knot nematodes other root-knot nematode species. The distribution of PRKN is not documented yet. Both walnut and almond are efficient hosts of the walnut root lesion nematode (RLN). These crops have long-term challenges with RLN, especially its primary host walnut that gets damaged by only one nematode per 250 cc of soil. No sustainable resistance and tolerance to RLN is currently commercially available in rootstocks of these crops.

The interaction of plant-parasitic nematodes and their hosts is two-fold. The one component is the response to nematode infection; some genotypes respond with no damage independent of the nematode reproductive potential on their roots (i.e., they are tolerant). Others may get hurt from only a few nematodes (i.e., they are sensitive/intolerant). As the second response, the roots may allow for nematode reproduction (susceptible) or they may prevent such (resistant). Both parameters are very important for the field performance of plants. Genotypes that are resistant but sensitive will cause tolerance without any resistance and can lead to build-up of nematode population densities that may cause problems for the following plantings.

Pistachio seemed free from these issues, likely based on a 1980s survey where no typical plant-parasitic nematodes at meaningful numbers were found on pistachio roots. In those days, the developing pistachio industry frequently used Pistacia atlantica as rootstock for the nut cultivars. Genotypes of this species were known to be on average resistant to RLN. In fact, some researchers used it as a resistant standard in their resistance determining studies. Growing P. atlantica rootstocks may have protected plantings from nematode infections.

Plant diameter of pistachio rootstocks UCB1 D71 and UCB1 D90 at the end of two growing cycles grown in microplots infested with increasing population densities of Pratylenchus vulnus. The threshold level is indicated by the red line. This is a modified reprint of a figure from Eur. J. Hortic. Sci. 89 (3).

While such rootstocks were useful regarding plant-parasitic nematodes, they were highly susceptible to Verticillium dahliae, the causal agent of Verticillium wilt that threatened the industry in the late 1980s. This crisis required major changes in the management of pistachio. While some optimization in cultivation of the crop could mitigate severe damage, ultimately, plants were required that would not be impacted by this soil-borne disease. Crosses of Pistacia atlantica and P. integerrima were identified as being resistant to Verticillium wilt.

Some hybrid rootstocks were used as seedlings (e.g., PG II or UCB1), but with the capacity of clonally propagating the genotypes in tissue culture, clonal rootstocks became more abundant. The name UCB1 is used for any clones out of that specific directed cross. Yet, there are distinct differences among UCB1 rootstocks. This is indicated by some nurseries by providing additional identification of specific clones. With this change in rootstocks, the genetic protection from plant-parasitic nematodes may be obsolete. In fact, screens of experimental UCB1 clones conducted by Dr. M. McKenry illustrated large variability of nematode susceptibility. In more recent screens with the most widespread nematode species at the Kearney Agricultural Research and Extension Center (KARE), susceptibility of different UCB1 clones was confirmed under field conditions.

In addition to the changes in rootstock genetics, pistachio is now frequently planted to fields that were used for the production of other perennial crops hosting plant-parasitic nematodes. In screens of pistachio, limited susceptibility to root-knot nematodes, nematodes feared after grape or cotton, was ascertained. In contrast, susceptibility to RLN was on a similarly high level as under other known tree nut crops. The build-up of these populations took long, but the principal susceptibility was confirmed. Such finding creates the potential challenge when pistachio is planted after almond and in particular after walnut. The latter crop is going through a phase of ample removal because of water restrictions, fumigant restrictions, and poor market conditions. Walnut rootstocks liable to have been used for decade-old walnut orchards are notoriously leaving behind concerning RLN population densities. This creates a potential risk for planting pistachio.

Current Threat of Root Lesion Nematode
Considering this background information, the question remains: How damaging is RLN to today’s pistachio plantings? The classical way to examine the damage potential of a plant-parasitic nematode on a specific crop is to expose the plant to increasing levels of the target nematode and measure growth response of the plants. In microplot experiments at KARE, such differing population densities were created by fractional fumigation that left behind varying population densities of RLN. Such plots were then planted to two different UCB1 clones that had tentatively shown different susceptibilities to RLN, and different overall vigor.

These trees were grown for two years. At the end of the second year, plant growth was measured and related to the initial population densities of RLN. With higher numbers of RLN, plants were weaker at this evaluation time, this was proportionally true for both rootstocks. In statistical analysis with the so-called “Seinhorst function,” the threshold level was determined where nematode numbers started causing damage to the trees. This level was around 13.3 vermiform nematodes per 250 cc of soil. Similar confirmatory results were found in a second microplot experiment (a more technical report of this study can be accessed at  pubhort.org/ejhs/ahi/1420/1420.pdf.)

Such population densities can be frequently found after a walnut orchard. So, care needs to be taken when pistachio follows walnut. Similar numbers can also be found after almond. Sampling is mandatory when replacing a tree nut crop with another. RLN infects the nut crops and the presumed benefits of “crop rotation,” or better crop change, do not encompass this nematode pest. It infects all three nut crops with differing damage potential. The recommendation is to sample fields for nematode detection holds (more soil sampling information and tips are found at youtube.com/watch?v=U7x0xHoKqC8.)

When diagnosing nematode problems in the field, those may often be overlooked. Pistachio orchards are cultivated under a rigorous pruning and training regimen. Some of the variability from tree-to-tree that would be a typical first indication of tree health issues may go unnoticed because of that. In addition, other soil differences may overlay areas where nematode infections are damaging and may lead to unwarranted conclusion of their responsibility for the differences detected. To bring more clarity to this topic, more field work is necessary. Especially the threshold level experiments require confirmation under commercial conditions. If readers were interested in participating in such studies, they are encouraged to reach out to the author Dr. Andreas Westphal at andreas.westphal@ucr.edu or 559-646-6555 to learn more on what is involved in such studies.

In summary, pistachio is not home-free from the risk for nematode damage. Vigilance and care need to be exercised when planning a new orchard planting. Soil sampling for nematode detection should be an instrumental procedure in this process.

Choosing an Organic Fertilizer Source? Consider Soil Temperature

By
Charlotte Decock | Associate Professor, Dept. of Natural Resources Management and Environmental Sciences, California Polytechnic State University, San Luis Obispo, Shane Egerstrom | Graduate Research Assistant, 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, San Luis Obispo and Lily Elola | Undergraduate Research Assistant, Natural Resources Management and Environmental Sciences, California Polytechnic State University, San Luis Obispo
-
0
Accumulation of mineralized nitrogen in the ammonium pool at lower temperatures has important implications for soil testing and strategic fertilizer placement (photo by Mark Bolda, UCCE.)

In organic crop production, fertilizers need to be mineralized by soil organisms before nitrogen becomes plant-available. Many factors can impact this mineralization process, including fertilizer chemical composition, physical fertilizer properties, soil properties and application method1–3. Moreover, microbial activity, including N mineralization, is affected by temperature4,5. Typically, an increase in N mineralization with increasing temperature is expected, but data is lacking to inform management decisions. Anecdotal evidence suggests organic fertilizer products perform differently based on the season in which the product is applied. This begs the question: Do organic fertilizer products show different sensitivities to soil temperature? We put this question to the test in a laboratory incubation study. 

Laboratory Incubation Study
We set up a laboratory incubation experiment in which soil was incubated with 12 organic fertilizers at 41, 50, 59, 69 and 77 degrees F for five weeks. Soil was collected from an organic vegetable field near Bakersfield, Calif. The soil was mapped at Milagro (coarse-loamy, mixed, superactive, nonacid, thermic Typic Torrifluvents), with soil analyses showing 64% sand, 18% clay and 0.6% soil organic carbon. The soil was sieved, homogenized and air-dried prior to incubation. Fertilizers were obtained from an organic vegetable grower and representative of commercially available products in the region. Fertilizers were categorized as dairy manure compost, chicken manure compost, bone meal dominated pellets, poultry litter dominated pellets and mixed feedstock pellets. The experiment was set up as a full factorial design, including 5 temperatures and 13 fertility treatments (12 fertilizer products and an unamended control), each replicated 4 times, for a total of 260 experimental units. For each experimental unit, we placed 250g of air-dried soil in plastic containers, rewetted to 60% water holding capacity and pre-incubated at the treatment temperature for seven days. Subsequently, fertilizers were added at a rate of 50 mg N/kg soil, roughly equivalent to incorporating 100 lbs N/acre in the top 6 inches of soil. We collected 5 g of soil from each experimental unit on days 0, 7, 14, 21 and 35 and analyzed for ammonium and nitrate concentration. The percentage of N mineralized was calculated as the difference in N concentration in the treatments receiving fertilizer compared to an unamended control divided by the total N applied.

Key Findings
Lowest N mineralization for dairy manure compost, highest for chicken litter compost

Nitrogen release varied drastically across fertilizer products and temperatures (Figure 1). Most products showed a net release of N, with up to 85% of fertilizer N released within the five-week incubation period. In some cases, we observed net negative mineralization rates up to -59%, indicating fertilizer addition caused immobilization of mineral N from sources other than the fertilizer. Dairy manure compost exhibited notably low N mineralization rates, ranging from -29% to 22%, with a mean of -1.4%. Other studies have found similarly low rates, with values mostly below 10%6–10. The carbon to nitrogen (C:N) ratios of dairy manure composts in our study were 11 and 13, within the range of ratios between 8 and 16 reported for other studies6,8. Mineralization rates for dairy manure compost trend low compared to rates expected based on C:N ratios2. In contrast, chicken manure compost showed higher mineralization rates (between 15% and 77%) with an average of 41%. Mineralization rates of chicken manure composts vary across studies. Rates of 25% and 54%11, 28% and 35%2, 100%12 and 0.4% to 6%13 have been reported. Variation in chicken manure compost mineralization may stem from differences in feedstock quality, including bulking agent and particle size as well as composting practices (e.g., turning and watering)14,15. Our findings indicate chicken manure compost performed similarly or slightly better than poultry litter pellets, though other studies reported higher rates for pellets2,6. High variability between studies underscores the need for case-specific evaluations of fertilizer effectiveness in agriculture.

Figure 1. Percent fertilizer nitrogen mineralized over the five-week incubation period by fertilizer category and temperature treatment. Different lowercase letters indicate significant differences in percent fertilizer nitrogen mineralized between fertilizer categories within a temperature treatment, averaged across the incubation period, based on the Dunn multiple comparison test with Holm adjustment.

The initial flush of soil organic N mineralization increased with temperature, but not fertilizer N release

The study found increasing temperature did not significantly increase the percent of N mineralized from fertilizers (Figure 1). In contrast, previous studies show varying responses. For instance, temperature moderately influenced mineralization in one study, increasing N mineralization from 56% to 66% as temperatures rose from 50 degrees F to 77 degrees F16. Another study observed a strong temperature effect on dairy manure N mineralization, with 24% occurring in summer (77 degrees F to 86 degrees F) and only 2% in winter (50 degrees F)10. The difference might be linked to the much higher application rates in those studies compared to this one. Further research is needed on the impact of application rates on N mineralization, especially considering the relevance for optimizing fertilizer timing (single vs split application) and placement (e.g., banding leads to more concentrated fertilizer placement than broadcasting). Like fertilizer mineralization, soil organic N mineralization in our study did not increase with increasing temperature during the 35-day incubation period, though soil mineral N content at the end of the pre-incubation did increase linearly from 42 mg N/kg at 41 degrees F to 49 mg N/kg at 77 degrees F (Figure 2). Other research has shown exponential increases in soil organic N mineralization with temperature beyond the pre-incubation period 5,17. Compared to other studies, our soil had a high sand content (>60%) and very low soil organic carbon content (ca. 0.6%), suggesting the characteristics of the soil and environmental factors like rewetting may play a role in temperature sensitivity of mineralization, which has implications for irrigation management.

Relative performance of fertilizer products varied by temperature

The ranking of mineralization rates among fertilizers varied by temperature (Figure 1). Bonemeal-dominated pellets ranked among the best products in terms of N release at temperatures of 59 degrees F and above, while chicken litter-dominated pellets ranked relatively high at 50 degrees F and 59 degrees F but performed worse above 68 degrees F (Figure 1). Other studies have found differences in the relative performance of organic fertilizers at different temperatures16,18, but clear insights on the fertilizer properties that lead to better performance at low vs high temperature are missing. Studies on decomposition of plant litter suggest decomposition slows down more severely with decreasing temperatures for ‘low-quality’ litter, such as roots, than ‘higher quality’ litter, such as shoots, but findings vary across studies4,19. With respect to N availability of organic fertilizers, not only temperature effects on N mineralization, but also temperature effects on loss pathways need to be considered. Ammonia volatilization is known to increase with increasing temperature and can constitute a substantial loss of N from organic fertilizers, especially in sandy and alkaline soils, but subsurface application and management of soil pH can help reduce loss20,21. Likewise, gaseous N loss through denitrification may be enhanced at higher temperatures22. Thus, organic fertilizer properties can affect both the temperature sensitivity of fertilizer N mineralization and loss pathways for released N. Growers may benefit from fine-tuning organic fertility management by season.

Low temperatures limit nitrification rates

Across fertilizer treatments, nitrate concentrations increased and ammonium concentrations decreased with increasing temperature (Figure 2), indicating an inhibitory effect of low temperature on nitrification as documented by previous studies16,23,24. Soil tests may underestimate plant-available N from organic fertilizers at colder temperatures since they typically report only nitrate. In our experiment, ammonium concentrations reached up to 35 ppm at lower temperatures, equivalent to approximately 70 lbs N/acre in the top 6 inches of soil. While both ammonium and nitrate are plant-available forms of N, the preferred ratio of ammonium to nitrate differs between crops and is affected by soil properties like pH25. Therefore, impacts of reduced nitrification due to low temperature on yield are expected to be context-dependent. In general, ammonium is much less mobile in the soil compared to nitrate26. This suggests placement of organic fertilizer closer to the plant roots (e.g., through banding) may be beneficial to increase N availability during colder periods as long as application rates are low enough to keep ammonium concentrations below toxicity levels27.

Figure 2. Soil nitrate and ammonium concentrations (in ppm N or mg N/kg soil) by temperature over the five-week incubation period for all 12 fertilizer treatments and the non-fertilized control. The Kruskal-Wallis rank sum test showed a significant effect on temperature and fertilizer treatment on nitrate and ammonium concentrations averaged across time. Dark blue = dairy manure compost, light blue = chicken manure compost, red = bonemeal dominated pellets, yellow = poultry litter dominated pellets, brown = mixed feedstock pellets and grey = unamended control soil.

Implications for Nitrogen Management in Organic Production
We wanted to find out if different organic fertilizers react differently to changes in soil temperature. Our research showed bonemeal-dominated pellets work better in warmer conditions, while poultry litter-dominated pellets perform better at moderate temperatures. Other studies also highlight temperature and soil type can impact how well fertilizers work. In general, our results caution against assuming fertilizers release N faster at higher temperatures. Mineralization of dairy manure compost was very low, even when considering the relatively high C:N ratio of 11 to 13, making it more useful for improving soil quality rather than as a primary fertilizer. Lower temperatures inhibited nitrification, which has been well documented in other studies. Accumulation of mineralized N in the ammonium pool at lower temperatures has important implications for soil testing and strategic fertilizer placement. Implications for yield are expected to be crop- and soil-dependent. Future research directions include how soil types, the impact of temperatures above 77 degrees F and higher rates of fertilizer affect N mineralization rates.

References
1. Cassity‐Duffey, K., et. al. Soil Science Society of America Journal 84, 534–542 (2020).
2. Lazicki, P., Geisseler, D. & Lloyd, M. Journal of Environmental Quality 49, 483–495 (2020).
3. Smith, R., et. al. California Agriculture 76, 77–84 (2022).
4. Fierer, N., et. al. Ecology 86, 320–326 (2005).
5. Miller, K., et al. Communications in Soil Science and Plant Analysis 50, 77–92 (2019).
6. Hartz, T. K., Mitchell, J. P. & Giannini, C., HortScience 35, 209–212 (2000).
7. Hurisso, T. T., et al. Organic Agriculture 2, 219–232 (2012).
8. Hurisso, T. T., et al. Agrosystems, Geosciences & Environment 7,
e20555 (2024).
9. Lehrsch, G. A., et al. Nutrient Cycling in Agroecosystems 104, 125–142 (2016).
10. Watts, D. B., Torbert, H. A. & Prior, S. A. Soil Science 175, 27 (2010).
11. Geisseler, D., et. al. Journal of Environmental Quality 50,
1325–1338 (2021).
12. Johnson, H. J., et al. HortTechnology 22, 37-43 (2012).
13. Tyson, S. C. & Cabrera, M. L. Communications in Soil Science and Plant Analysis 24, 2361–2374 (1993).
14. Leconte, M. C., et al. Biology and Fertility of Soils 47, 897–906 (2011).
15. Shi, W., et al. Applied Soil Ecology 11, 17–28 (1999).
16. Hartz, T. K. & Johnstone, P. R. HortTechnology 16, 39-42 (2006)
17. Dessureault-Rompré, J. et al. Geoderma 157, 97–108 (2010).
18. Thangarajan, R., et al. Environmental Science and Pollution Research 22, 8843–8854 (2015).
19. Conant, R.T., et al. Global Change Biology 17, 3392–3404 (2011).
20. Terman, L. Advances in Agronomy 31, 189–220 (1979).
21. Wester-Larsen, L., et al., Journal of Environmental Management 323, 116249 (2022).
22. Dai, Z. et al. Global Change Biology 26, 5267–5276 (2020).
23. Sims, J. T. Journal of Environmental Quality 15, 59–63 (1986).
24. Tisdale, S. L. Soil Fertility and Fertilizers (1993).
25. Chen, J. et al. Field Crops Research 307, 109240 (2024).
26. Norton, J. & Ouyang, Y. Front Microbiol 10, 1931 (2019).
27. Esteban, R., et al. Plant Science 248, 92–101 (2016).

Evaluation of Equipment for Improving Management of Drip Systems in Row Crops

By
Michael Cahn | UCCE Irrigation and Water Resources Advisor, Monterey County
-
0
Figure 1. Average application rate of a drip system where the main valve is manually adjusted by an irrigator at the beginning of the irrigation set.

With ever-stricter regulations, growers will need to implement best management practices that lessen water quality impairments to surface and groundwater. Also, implementation of the Sustainable Groundwater Management Act will require growers to use water as efficiently as possible to produce their crops. A well-designed irrigation system that is properly managed and maintained is key to using water efficiently and preventing nutrient and pesticide losses that degrade water quality. State and federal programs, such as the State Water Efficiency and Enhancement Program and NRCS Environmental Quality Incentives Program, can finance equipment that improves the efficiency of irrigation systems.

Previous research in row crops has shown many drip irrigation systems could be better optimized through improved pressure regulation and careful monitoring of applied water using flowmeters. When pressure in drip systems is not accurately regulated and monitored, the application rate will vary during and between irrigation sets. Figure 1 shows the average application rate of a drip system when the main valve of the block is adjusted manually by an irrigator to achieve a desired pressure. The fluctuation in pressure among irrigations causes the drip system to have 33% variation in the application rate during the crop cycle.

This uncertainty in the system application rate limits the ability to accurately schedule how long to irrigate. A drip system that applies 0.12 inches per hour would need 8.3 hours to apply an inch of water. Under higher pressure conditions, the same system may have an application rate of 0.15 inches per hour and would only need to be operated 6.6 hours to apply an equivalent volume of water.

During the past few years, we have been evaluating equipment that can help growers irrigate with drip more precisely. Some of these tests were conducted under controlled conditions and others were done by trialing equipment in commercial fields.

Field Evaluation of Two Types of Pressure-Reducing Valves
Pressure-reducing valves (PRV) are valves that can automatically adjust the cross-sectional area of a passageway through which water flows to maintain a desired pressure downstream. When the downstream pressure rises above a threshold, the valve will automatically reduce the size of the passageway to restrict flow, and when pressure drops below a threshold, the valve will open the passageway to increase flow. PRVs can also be used like a regular valve to turn on and off the flow of water.

Figure 2. Netafim (left) and Nelson (right) pressure-regulating valves that were tested on drip systems installed in a 7.5-acre vegetable field.

We tested two types of PRVs in drip systems installed in a commercial vegetable field: the Netafim 90 series and the Nelson 800 series valves (Figure 2). Most PRVs use a mechanism similar to the Netafim 90, which has a bonnet with an internal rubber diaphragm that expands and contracts to adjust the flow rate, thereby maintaining a desired downstream pressure. In contrast, the Nelson 800 series uses a flexible rubber sleeve that expands and contracts around an internal cage to regulate flow and achieve a desired downstream pressure. Both models use a pilot with a mechanical spring to adjust the downstream pressure or set point of the regulator. The pipe diameter of both models tested was 6 inches and rated for the range of flow rates expected in the drip system that was installed in a 7.5-acre vegetable field. Both PRV models are available in smaller and larger diameters than 6 inches. Nelson offers a nylon version of the 800 series in the 1000 series model, which is limited to pipe diameters of 4 inches or less. Our objective was to evaluate how well the PRVs maintained the pressure between 8 and 10 psi in the submain with minimal adjustments during an irrigation set.

The Netafim 90 PRV was found to respond slowly to sudden increases in upstream pressure, which sometimes caused drip tape to either detach from the submain or burst under the excessive pressure. Additionally, the pilot on the Netafim 90 had to be adjusted several times during the irrigation set to maintain the pressure in the desired range of 8 to 10 psi.

The Nelson 800 PRV was found to adjust faster to increases in upstream pressure compared to the Netafim PRV. Also, the Nelson PRV only occasionally needed to be adjusted during an irrigation set. Figure 3 shows the upstream and downstream pressure of a 6-inch-diameter Nelson 800 PRV for several irrigation dates. Average downstream pressure was maintained at 10 psi despite fluctuations in upstream pressure ranging from 30 to 50 psi.

Figure 3. Pressure measured upstream and downstream of the Nelson 800 pressure reducing valve in a drip irrigated lettuce field. Upstream and downstream pressure were monitored using pressure transducers. Average downstream pressure was maintained at 10 psi despite fluctuations in upstream pressure ranging from 30 to 50 psi.

An important tip an irrigator involved with the field testing learned was at the start of an irrigation, the main valve for the block should be partially opened to allow the drip system to slowly come up to pressure. After the PRV begins regulating the pressure of the drip system, the block valve can be fully opened.

Accuracy of Flowmeters
Flowmeters are quite useful for scheduling irrigations and diagnosing problems that may occur in an irrigation system. Flow rates greater or less than normal may indicate leaks, plugging of emitters or sprinkler nozzles, or if the system is operating at too high or low of a pressure. Scheduling irrigations based on estimates of crop evapotranspiration requires converting between inches of water depth to gallons of water. Gallons of water applied can be converted to inches using the equation:

Inches of water applied = Total gallons of water applied ÷ [27,154 × acres of irrigation block]

Also, the time needed to apply a desired depth of water can be determined from flow rate:

Irrigation set time (minutes) = [depth of water (inches) × 27,154 × acres of irrigation block] ÷ flow rate (gal/min)

The accuracy and reliability of several models of flowmeters suitable for measuring the volume of water applied to an irrigation block were evaluated. The models included Seametric AG3000, Netafim Octave, Seametric AG90, Bermad M10 and the Netafim WST (Fig. 4). Except for the Netafim WST, all models have no moving parts, and most minimize turbulence so that the required length of straight pipe before and after the meter ranges from two to five pipe diameters. The AG3000, AG90 and M10 use magnetic sensors to measure flow rate. The Octave monitors flow using an ultrasonic sensor. The Netafim WST uses an impeller to measure flow which causes minimal loss of pressure across the meter. All models have digital registers and have an output cable that can interface with dataloggers so flowrate can be monitored remotely. Two AG3000 meters were included in the testing to evaluate if they provide similar measurements of flow.

Figure 4. Flowmeter models tested included A) Seametric AG90, B) Bermad M10, C) Netafim WST, D) Netafim Octave and E) Seametric AG3000.

The accuracy of the various flowmeters was evaluated by assembling each model in series along a 6-inch-diameter main line separated by at least 3 feet of straight pipe. The average flow rate evaluated was ~330 gallons per minute, and each evaluation lasted about half an hour. Approximately 10,000 gallons of water were pumped through the main line, and the total volume recorded by each meter was noted at the end of the irrigation set. The evaluation process was repeated five times so the average and standard deviation of the total volumes could be calculated for each flowmeter model. Because the volume of water pumped through the meters was large and could not be physically measured, values recorded from each meter were compared relative to the mean volume of the group of meters tested.

Results of Flowmeter Testing
Most flowmeters had less than ±1.5% difference from the mean volume calculated for the group of meters, demonstrating they had similar estimates of flow (Table 1). The Netafim Ultrasonic and Seametric AG3000 meters were the closest to the mean volume. The Netafim WST, which has an impeller, was consistently less than the mean volume. The Seametric AG90, which inserts into an irrigation pipe, provided the next lowest estimates of flow volume, and the Bermad M10 gave the highest estimate of flow volume, averaging 1.7% higher than the mean volume. Note the two AG3000 meters measured very similar volumes.   

Table 1. Flowmeter estimates of water volume in gallons and percentage difference from the mean volume of all meters evaluated.

The accuracy and reliability of several flowmeters and PRVs were evaluated through field testing. These tests were done on a limited number of models, and other options are likely available that have equal or better accuracy and reliability than the equipment tested in this study. Nevertheless, these evaluations identified several models of flowmeters and PRVs that appeared to be accurate and reliable and could potentially greatly improve the operation of drip irrigation systems installed in row crops.    

This project was supported by the California Leafy Green Research Board.

123...38Page 2 of 38
-Advertisement-



EDITOR PICKS

POPULAR POSTS

POPULAR CATEGORY

©