Figure 1. Reduction of the frequency of foggy days in the Central Valley. Photographs exemplify a winter foggy day and a sunny day in a cherry orchard when tree temperature is respectively similar and greater than air temperature.
Fruit trees need low temperatures during the winter season to break dormancy and ensure synchronized fruit development during the growing season. If winter is warm, bloom will be inadequate, delayed and uneven, cross-pollination will be limited, and fruit set will be reduced, resulting in varying crop sizes and maturity stages at harvest time, which can further reduce yield and substantially impact growers’ returns. To overcome low chill, growers rely on chemical rest breaking agents that ‘mitigate the lack of chill,’ advance and condense bloom and ensure sustainable yields and profitability. However, these products must be applied at the right time to be effective and reduce the risk of phytotoxicity. The time to apply dormancy-breaking agents is currently based on the accumulation of a certain level of chill, given a certain chill model.
Figure 1. Reduction of the frequency of foggy days in the Central Valley. Photographs exemplify a winter foggy day and a sunny day in a cherry orchard when tree temperature is respectively similar and greater than air temperature.
Chill Accumulation Models
Different models to calculate winter chill accumulation are available for growers. Some models consider chill hour accumulation as the number of hours below 45 degrees F. The more recent and complex model, referred to as the Dynamic Model, also considers the loss of chill when temperatures are warm for calculating the chill portions. However, all these models have shown differences among locations and years, with this inconsistency being amplified by climate change. These inconsistences have significantly reduced model reliability with profound effects on growers who rely on these calculations for important management practices, such as selecting appropriate cultivars or timing the application of dormancy-breaking products. One weakness of all these models is they base chill accumulation calculation using air temperature as the only environmental factor.
Climatic Shifts and Impact on Chill Accumulation Calculation
Prolonged periods of fog in the Central Valley contributed significantly to chill accumulation in this region. However, the intensity and duration of this fog declined significantly over the years. Analyses of climate from Baldocchi and Waller from UC Berkley published in 2014 showed a reduction of the number of winter fog events in the Central Valley of California by 46% over 33 years. This climate change is reducing chill accumulation and, importantly, is reducing our capability to properly predict chill accumulation with the currently available models based on air temperature only. In fact, on foggy days tree temperatures are very similar to air temperatures (opposite to sunny days when radiation directly heats the tree), leading to tree branches and main scaffolds becoming warmer than air temperature (Figure 1). Thus, air temperatures would reflect the temperatures trees are experiencing on foggy days but not on clear-sky days. Growers have been observing these changes happening for decades now, and researchers have described them in scientific publications, but we still do not have any practical tool to integrate these climatic shifts in our orchards management practices.
Measuring Tree Temperature in California Cherry Orchards
Supported by the California cherry industry, we started in 2020 a series of research trials aiming to characterize cherry tree temperature under different growing conditions. Our final objective was to integrate tree temperature in the chill accumulation models. This would increase their accuracy in predicting chill accumulation, since it is more representative of tree real condition than air temperature, especially in warm and sunny winters.
A large dataset of environmental and physiological parameters was collected for three consecutive seasons in three commercial cherry orchards located in the Lodi (San Joaquin Valley) and Bakersfield (Kern County) areas. We installed meteorological stations in the field to measure weather (mainly air temperature and solar radiation). Tree bark temperature was monitored by inserting thermocouples (very small temperature measuring sensors) just below the bark of branches located at the four cardinal points as demonstrated in Figure 2. As expected, trees were warmer than the air most of the time during clear days. The average difference between tree and air temperatures was about 10 degrees F. The largest temperature difference between trees and air was recorded in the southernmost orchard, where the bark of south-exposed branches was 20 to 25 degrees F warmer than the air.
Figure 2. Seasonal trend (hourly values) of air temperature (red) and tree temperature (blue). Tree temperature was measured with a thermocouple installed below the bark in the south exposed side of a main branch in a cherry orchard located in southern California.
Tree Chill Accumulation
Using tree temperature instead of air temperature, chill accumulation is lower by about 8 to 12 chill portions. This quantity was not constant between locations, years and branch exposures, as mainly affected by climate conditions. For example, in the San Joaquin Valley, 2021-22, which was a relatively warm winter, the south-exposed branches accumulated 14 chill portions less than the air; in 2022-23, which was a very cold winter, the south-exposed branches accumulated only 5 to 6 chill portions less than the air.
Development of the TreeChill Model
The large dataset collected during the three years of project was used to develop the TreeChill model, a grower-friendly tool that predicts tree temperature based only on environmental parameters easily achievable from public weather stations. The model is highly accurate right now for predicting the temperature of cherry trees located in growing areas where the experiment was performed. As it can be observed in Figure 3, the chill accumulation predicted using the TreeChill model (blue line) is extremely close to the measured tree temperature (black line) and always lower than the measured air temperature (orange line).
Table 1. Chill Portions accumulated from November to March for two experimental locations and two winter seasons and calculated using the air temperature and the bark temperature measured in branches exposed to South and North.
Future Work
We are now working on publishing the TreeChill calculator as an online tool through our Lab website (Tree System Lab at UC Davis) and the Fruit and Nut Research and Information Center website. The calculator automatically uses the data from the CIMIS, so researchers and growers will only need to input their orchard location and they will have access to tree temperature data and chill accumulation calculated using tree temperature as an input instead of air temperature. Next step will be creating a correlation between TreeChill and AirChill for different years and locations so we can start to implement tree temperature in grower management decisions, including dormancy breaking agent applications, cultivar selection, pest control, etc. In the future, we plan to adapt the model to different crops and locations.
Figure 3. Chill portion accumulation since November 1 calculated using the tree temperature predicted by our TreeChill model (blue lines), the tree temperature measured with thermocouples (black line) and the air temperature (orange line) from CIMIS for three seasons in the Kern County orchard.
Need of K as the tomato plant begins to enter reproductive phase.
Nitrogen, phosphorus and potassium (NPK) are three major nutrient components of any fertility program and are developed to maximize crop uptake at a given growth stage. Most nitrogen is applied in-season via fertigation (in California) utilizing common materials such as urea, UAN, CAN17 and CN9. Phosphorus is applied early season or in-season based on crop need and timing. Potassium has become a hot topic over the past 10 years and has evolved from the bulk of K2O being applied preplant or in dormancy to in-season applications to maximize efficiency. In this article, we will discuss the need of applying K in-season via fertigation in annual and perennial crops.
K as an Essential Plant Nutrient
The common practice of applying K preplant for annuals and in the dormant season for permanent crops is an effective method of applying K because it isn’t prone to leaching as negatively charged elements. However, depending on your soil type, K can tie up in heavy clays, especially when soils are dry. While K doesn’t readily leach through a soil profile it is important to have adequate K soil levels when the crop needs it, preferably in the vicinity of the feeder roots. This is especially important in the summer when evapotranspiration is at its peak. Reminder that K is heavily involved with the opening and closing of the stomata through the guard cells by turgor pressure, which is important for water use efficiency. Plants exposed to growing media with adequate levels of K are more tolerant to drought conditions, suffer less and negative effects on crop yield and quality due to drought conditions are reduced.
Liquid K Options
There are a variety of liquid K sources commonly used in California, all of which have their place in fertility programs. MOP and SOP have been standards for many years. With the introduction of potassium thiosulfate, many advisors have made it their standard due to its high K content (25%) and thiosulfate which adds additional benefits. Potassium hydroxide has also found a place in California agriculture and has increased in use. Potassium nitrate is fairly new to the California market and has been adopted in many programs due to its ability to blend with other fertilizers like CAN 17 and CN9. High-efficiency K products are widely utilized and, often, are proprietary to retail chains. With all that said, there are many, many options available to inject K in-season.
A key factor in deciding the most suitable K source for your fertilization program is to consider the secondary element that will be supplied with the K (e.g., with MOP, chloride will be added in the system; with SOP and KTS, sulfur will be added; with potassium nitrate, nitrogen will be added in the system; etc.). Therefore, considering the impact of these elements on the balance of the final nutrient solution will also influence crop yield and quality.
Current Practices
Given high fertilizer prices the last few years, we’ve backed off on fall-/winter-applied K applications, especially in almonds where we have successfully mined existing soil K. I am not a grower myself, but I hear from several advisors reducing K in the dormant season hasn’t yet influenced yield or K levels in tissues. This makes a case that perhaps we should be backing off on applying K in the fall/winter to permanent crops. And, perhaps, we should consider doing the same in annual crops, applying less K in preplant and taking a “spoon-feeding” approach, following the nutrient absorption demand of the crop by phenological stage. There is much data suggesting spoon feeding, or continuous fertigation, is beneficial to yield and quality.
The Benefits of Continuous Fertigation
Continuous fertigation is a nutrition management strategy that is built on the principle of small doses of mineral fertilizer with every irrigation event (some may call this ‘spoon-feeding.’) This type of management strategy requires knowledge of input interactions in the plant and soil interface, proper infrastructure for accurate input delivery and decision support tools for proper adaptation. Nitrate-based offerings are considered best suited for these spoon-fed strategies because they move predictably with water through the profile, are plant-available at the time of application and increase uptake of positively charged elements (cations) like calcium and magnesium among others. The agronomic benefits of spoon-feeding N through nitrates are undeniable, and the 4Rs (right source, right place, right rate and right time) should be considered with K as well regarding continuous fertigation.
Permanent Crops
In the case of citrus, the peak need for K begins at fruit set and drops off severely postharvest.Table grapes show a similar trend, although after fruit set, a very high and consistent need for K is required.Direct correlation between K levels and evapotranspiration (ET). While we tend to apply the bulk load of K in the dormant months, it’s important K soil content is maintained May through August, the hottest months of the year.
Annual Crops
Annual crops are managed slightly differently than perennial crops in that there may or may not be adequate soil K levels at planting based on the previous crop. A soil test is imperative to determine a fertility program for not just K but all essential nutrients. Given annual crops are on a shorter growth cycle, the importance of in-season K applications should be a priority, and, in many cases, can have a greater impact on yield and quality.
Applying K in-season via fertigation isn’t a new concept; most advisors’ recommendations include liquid K sources in their programs. We’ve seen in recent years reducing the amount of K we apply in the dormant season doesn’t affect yield or quality in most cases. However, following tissue K levels in-season in this case becomes even more important to avoid K deficiency. Rather than banking on existing soil K levels, we should be analyzing tissues consistently and creating prescriptive K recommendations based on the crops’ need. The data indicate that need is in-season. We have many K-based fertilizer options available in California, and we should determine which to use based on crop uptake, temperature, soil moisture and secondary element. And, of course, always consider the 4Rs concept to maximize uptake, efficiency and cost.
Similarly, cantaloupes require more K as the plant begins to produce fruit.
Oregon State University's Surendra Dara is currently conducting a survey specifically about the use of biologicals for pest management in California. Data from this anonymous survey will be used for a report along with the data from a recent survey on pest management needs in the Pacific Northwest. Fill out the survey at oregonstate.qualtrics.com/jfe/form/SV_2t6szOEbmryTpNs.
As food production faces the persistent threat of endemic and invasive pests, researchers continue to develop new technologies and strategies for protecting crops from these threats. One such new technology is RNA interference (RNAi) with targeted mechanisms toward specific pests. RNAi can be used as a trait in a crop or as a sprayable product against the target pest. Before delving further into this, here are a few basic details of this biological process that will help understand the RNAi mechanism.
Deoxyribonucleic acid (DNA) in the chromosomes of most living organisms contains genetic code for making proteins that are essential for various biological processes. Ribonucleic acid (RNA) carries the genetic code from DNA to the protein-making factories within the cell known as ribosomes. DNA has two strands of nucleotides (sets of deoxyribose sugar with nitrogenous bases connected by a phosphate group) whereas RNA has only one strand. RNA also differs from DNA in having ribose sugar, instead of deoxyribose, and a different kind of nitrogenous base. The purpose of RNA is to transfer the genetic code from DNA as amino acids are made in ribosomes. A chain of amino acids makes a specific protein. Examples of proteins in insects include juvenile hormones responsible for development and reproductive maturation; ecdysone responsible for molting and metamorphosis; digestive enzymes like amylases, glycosidases, lipases and proteases; and esterases that are important in metabolizing various compounds that regulate behavior, development, insecticidal resistance and other processes.
RNAi involves silencing the expression of a specific gene by double-stranded RNA (dsRNA) pieces (either small interfering RNA or microRNA each containing about 21 to 23 nucleotide pairs) attaching to messenger RNA (mRNA) carrying the code from DNA and thus interfering with the production of a specific protein. RNAi is also known as post-transcriptional gene silencing because the silencing is done after the DNA code is transcribed to mRNA. RNAi is a natural phenomenon that helps organisms to defend against infections or regulate gene expression. For example, when there is a viral infection, cells activate RNAi to destroy virus particles. RNAi-based therapies are currently used in the medical field to treat cancer and neurological issues and to regulate oxalic acid in urine or the low-density lipoprotein cholesterol in blood.
Use in Agricultural Crops
RNAi can be used in agriculture for improving yield or quality, imparting abiotic stress tolerance or pest resistance and incorporating other desirable traits or as biopesticides in crop protection (Bharathi et al. 2023; Chaudhary et al. 2024). Many research studies have been exploring the RNAi potential in agriculture for decades (Fletcher et al. 2020). Modifying plant height in apple (Zhao et al. 2016), rice (Qiao et al. 2007) and tomato (Cheng et al. 2020); imparting drought, salt and heat tolerance in cotton (Abdurakhmonov et al. 2014), abiotic stress tolerance in cereal crops (Dubrovna et al. 2023) and cold tolerance in tomato (Jiao et al. 2024); imparting resistance to blast (Magnaporthe grisea) and leaf blight (Xanthomonas oryzae pv. oryzae) in rice (Jiang et al. 2009), citrus canker (Xanthomonas citri subsp. citri) in citrus (Enrique et al. 2011), late blight (Phytophthora infestans) in potato (Eschen-Lippold et al. 2012), Fusarium head and seedling blight (Fusarium graminearum) in wheat (Cheng et al. 2015), soybean mosaic virus in soybean (Kim et al. 2016); imparting resistance to bollworm (Helicoverpa armigera) in cotton (Mao et al. 2007 and 2011) and resistance to brown planthopper (Nilaparvata lugens) in rice (Zha et al. 2011); and imparting resistance to root-knot nematode (Meloidogyne incognita) in tomato (Dutta et al. 2015) and soybean cyst nematode (Heterodera glycines) in soybean (Guo et al. 2015) are some of the examples of improving crop traits.
The first RNAi crop in the U.S. was corn (SmartStax® PRO) against the western corn rootworm (Diabrotica virgifera virgifera) containing both Bacillus thuringiensis toxins and RNAi technology (Head et al. 2017). With its ability to resist both belowground and aboveground lepidopteran pests, this hybrid is an important IPM tool. This hybrid is also available in Canada for cultivation, and grain and products from the hybrid are approved for consumption in the European Union. RNAi-based crops are not considered genetically modified organisms (GMOs) because they do not contain a foreign gene to express a particular protein like GMOs but use a natural mechanism to silence a particular gene.
In addition to adding desirable traits to crops, RNAi has also been explored or developed for treating plants against pests and diseases. While RNAi crops use the host-induced gene silencing (HIGS) method, RNAi biopesticides use the spray-induced gene silencing (SIGS). SIGS has been explored for controlling Fusarium graminearum in barley (Koch et al. 2016), sucking and/or stem-boring insects in multiple crops (Li et al. 2015; Hunter and Wintermantel, 2021; Jain et al. 2022) and hawthorn spider mite (Amphitetranychus viennensis) in fruit trees and woody ornamentals (Yang et al. 2023). The first sprayable formulation of RNAi-based biopesticide is CalanthaTM from GreenLight Biosciences against the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Rodrigues et al. 2021). The active ingredient is a dsRNA molecule known as Ledprona (Leptinotarsa decemlineata-specific recombinant double-stranded interfering Oligonucleotide GS2). It belongs to a new class of insecticides under group 35 as an RNAi-mediated target suppressor. Applied as a foliar spray, Ledprona suppresses the gene that produces proteasome subunit beta type-5 (PSBT5) in CPB and arrests insect feeding within two to three days after it is ingested, leading to the death of the pest. PSBT5 is an essential protein important in maintaining cellular protein quality by degrading damaged or misfolded proteins or proteins that are no longer needed.
RNAi mechanism for gene silencing through a crop trait or a sprayable product (graphic by S. K. Dara, courtesy BioRender.)
RNAi can also be used to protect honey bees from the Israeli Acute Paralysis Virus (Hunter et al. 2010) and the Varroa mite (Garbian et al. 2012). In field studies, honey bee populations and honey production increased when bees were fed dsRNA for the virus in the presence of virus in the colonies (Hunter et al. 2010). The ectoparasite Varroa mite is a major threat to the honey bee colony health and its management is a significant challenge. When honey bees ingest the mite-specific dsRNA that silences the calcium ion-binding protein known as calmodulin, the dsRNA is transmitted to the Varroa mite feeding on the hemolymph of the bees, resulting in mite mortality (Garbian et al. 2012).
Minimal Environmental Risk
As with any new technology, it is important to consider the impact of RNAi on the environment and non-target organisms. Environmental risks and regulatory aspects of RNAi-based products have been reviewed in various reports (Liu et al. 2021; De Schutter et al. 2022; Christiaens et al. 2022). Microbial activity, UV radiation and other environmental conditions degrade dsRNA, and they are generally less stable in the environment, especially under the field conditions where they are used (Bachman et al. 2020). Studies showed dsRNA degraded within two days in soil and one to three days in aquatic environments (Dubelman et al. 2014; Fishcer et al. 2017). Chen et al. (2023) reported while an RNAi-based biopesticide was highly effective against the 28-spotted ladybeetle (Henosepilachna vigintioctopunctata), a pest of solanaceous crops, it had no non-target effect on the predatory lady beetle Propylea japonica. Similarly, studies showed the dsRNA developed for controlling Varroa mite were safe for honey bees (Tan et al. 2016; Vélez et al. 2016) and the monarch butterfly (Danaus plexxippus) whose calmodulin mRNA has a slight match to the Varroa-active dsRNA (Krishnan et al. 2021).
With regards to Ledprona, the U.S. Environmental Protection Agency (EPA) found it has minimal human and environmental risks due to low application rates, rapid microbial degradation in the environment and physiological barriers and degradation mechanisms in mammals. U.S. EPA also gave Ledprona a “No Effect” determination according to the Endangered Species Act.
Environmental instability is one of the concerns for SIGS, but formulation technology can address this problem. Instead of spraying naked dsRNA, formulating it with layered double hydroxide clay nanoparticles known as BioClay significantly extended the stability of dsRNA. Spraying dsRNA in BioClay provided protection against pepper mild mottle virus and cucumber mosaic virus at least for 20 days, and dsRNA was detected on the leaves 30 days after application (Mitter et al. 2017). Similarly, spraying BioClay-formulated dsRNA 5 days before exposing to virus-containing green peach aphids (Myzus persicae) offered protection against the bean common mosaic virus in cowpea and benth (Nicotiana benthamiana) (Worrall et al. 2019). In a more recent study, BioClay-formulated dsRNA against gray mold (Botrytis cenerea) increased disease protection from one week to three weeks on leaves and five days to 10 days on fruit (Niño-Sánchez et al. 2022).
Arthropod pests and pathogens are resilient and rapidly evolving organisms and can develop resistance to RNAi technology just like they develop to pesticides or transgenic crops. Whether it is HIGS or SIGS, avoiding heavy reliance on one tool and adopting integrated pest management (IPM) and resistance management strategies is crucial even when using RNAi. An IPM strategy that takes advantage of multiple tools will minimize the risk of resistance development while achieving desired pest suppression.
Resources
Videos about RNAi: https://youtu.be/xDg6pu7HWz4 and https://youtu.be/cK-OGB1_ELE
For the full list of references, visit ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=59299.
Comparison of grower standard (left) and EarthMAX treated beds (right)
As the demand for sustainable and eco-friendly agricultural practices grows, biostimulant products have emerged as key players for enhancing crop productivity while minimizing environmental impact. According to USDA 2019 report, A plant biostimulant is a substance, microorganism, or mixtures, that, when applied to seeds, plants, the rhizosphere, soil or other growth media, act to support a plant’s natural nutrition processes independently of the biostimulant’s nutrient content. Plant biostimulants contain an array of substances and/or microorganisms that stimulate growth of plants through diverse mechanisms such as an efficient absorption of nutrients by plant roots or their use in the plant tissue. This efficiency results in stress mitigation, improved yields, and reduces the need for excessive fertilizer application. As California faces challenges related to water scarcity and degrading soil health, biostimulants offer a sustainable solution by maximizing the use of available resources.
California’s diverse climate expose crops to various environmental stresses, such as drought, heat, and salinity. Biostimulants help plants build resistance to these stressors, ensuring better crop performance even in challenging conditions. This is particularly crucial in a state where water resources are often limited. Biostimulants pro-mote a healthy soil microbiome, fostering beneficial microbial activity. A balanced soil microbiome contributes to improved nutrient cycling, disease resistance, and overall soil structure. This is essential for sustaining the long-term productivity of California’s agricultural lands. With increasing awareness of the environmental impact of conventional farming practices, there is a growing interest in sustainable alternatives. Biostimulants align with the principles of sustainable agriculture by minimizing the use of synthetic chemicals and promoting a more ecological approach to crop management.
AgroPlantae has been producing and researching biostimulants for the last 15 years, with tailored applications for diverse crops and weather conditions. Among our products, EarthMAX is a biostimulant derived from amino acids, acts as a rapid-action nutrient synergist. This soil-applied biostimulant reinvigorates vegetative development, functioning as a catalyst for nutrient uptake and delivering an energy boost during environmental or physiological stress. EarthMAX elevates overall crop quality by offering specialized plant extracts for immediate uptake and benefits. By enhancing crop resilience to stress, EarthMAX optimizes fruit retention, quality, and yield , even at a low application rate of 1-2 pints per acre. In this article we focus on EarthMAX research trials conducted in California in collaboration with tomato growers. EarthMAX demonstrated a substantial increase in marketable yield, providing growers with a high return on investment.
California produces about one third of world’s and 95% of nation’s processing tomatoes. California tomatoes, characterized by their superior quality and prolific production, are subjected to various environmental stresses and nutrient limitations that can impact overall crop yield. To address these challenges, the utilization of biostimulants has garnered attention. Biostimulants has been proven to exert a beneficial influence on plant growth and development by promoting better nutrient uptake, plant growth and higher fruit development.
AgroPlantae has conducted a two-year trial on Processing Tomato. A first trial was conducted in Stockton, CA, in 2022, and involved three applications of EarthMAX at a rate of 1 pint/acre at key growth stages: 7-10 days post-transplant, 50% bloom, and fruit enlargement. Post-application, we assessed yield and quality parameters, revealing a remarkable 16% in-crease in marketable yield. This boost in marketable yield is reflected in the reduction of defects caused by mold, irregular fruit size, sunburn, and other factors. Treated tomatoes exhibited a 1.2% lower mold, 3% lower defects, a 1.2 unit increase in average tomato size, and a noteworthy 0.2 Brix content elevation than the grower standard product. The return on investment was 7319%.
Figure1: Tomato yield for trial conducted in Stockton, CA (2022).
A second trial was conducted in Riverdale, CA, in 2023, and involved two applications of EarthMAX at a rate of 1 pint/acre during crucial growth stages (7-10 days post-transplant and 50% bloom). The trial showcased impressive results: EarthMAX delivered a remarkable 13% increase in marketable yield, evident in the reduction of defects caused by mold, irregular fruit size, sunburn, and more. This translated to an ROI of $800+ per acre based on the 2023 tomato market price of $138/ton.
Figure 2: Tomato yield for trial conducted in Riverdale, CA (2023).
Comparing the EarthMAX treated area to the grower standard product, there was a notable enhancement with 7 ton/acre more yield, 0.285 % less green, 0.6 unit increase in size, and a 0.4 Brix content boost. In the same 2023 processing tomato trial in Riverdale, CA, processing tomatoes experienced a substantial growth response, plant height and establishment improvement. EarthMAX, applied 7 days post-transplant, outperformed GS, which only received the standard fertility program. Ten days after the initial application and continuing through to yield, EarthMAX-treated plants displayed greater height and vigor compared to GS treatment. The return on investment was 3625%.
In conclusion, EarthMAX by AgroPlantae showed excellent results in California tomato trials, elevating marketable yield and enhancing fruit quality. As a trusted and efficient biostimulant in AgroPlantae’s product line, EarthMAX addresses the challenges of diverse agricultural conditions, providing growers with a reliable solution to optimize crop performance in California’s vital tomato industry.
Visit AGROPLANTAE.COM or give us a call (559) 498-0388 to learn more
Growing the Crop Consultant Industry One Reader at a Time
Readership studies play a crucial role in the agricultural sector, particularly for specialized industries like crop consulting. These studies help publications like Progressive Crop Consultant understand their audience better, enabling them to tailor content to the specific needs and interests of CCAs, PCAs, professional agronomists, soil specialists and more. This targeted approach is vital for fostering a thriving agriculture industry.
Firstly, readership studies provide valuable insights into the preferences and information needs of industry professionals. By analyzing data on what topics are most read and appreciated, Progressive Crop Consultant can focus on producing relevant and engaging content. This could range from the latest pest management strategies to water and nutrition. Such information not only keeps readers informed but also helps them make better decisions for their growers and themselves, ultimately leading to improved crop yields, quality and business success.
In a recent Baxter Research Center media study in Progressive Crop Consultant, 48 CCAs, PCAs, professional agronomists, soil specialists and more shared overwhelmingly positive feedback.
“Good up-to-date information,” said one respondent.
“Very good articles written by unbiased experts and contributors,” said another respondent.
“These [articles] allow me to discuss with my customers and find out what possible purchasing strategies there might be,” another said.
Secondly, readership feedback is essential for fostering a sense of community within the industry. When crop consultants actively participate in readership studies, they contribute to the creation of a publication that truly represents their collective voice and concerns. This collaboration can lead to the sharing of innovative ideas, experiences and best practices, further strengthening the industry as a whole.
Moreover, providing feedback to Progressive Crop Consultant can help address specific challenges faced by the industry. For instance, concerns about climate change, pest management or water can be highlighted and addressed through in-depth articles and expert opinions. By understanding these issues, the magazine can play a pivotal role in advocating for the industry and influencing policy decisions that benefit consultants and ultimately growers.
In conclusion, readership studies are indispensable for a niche publication like Progressive Crop Consultant. They enable the publication to produce content that is not only informative and engaging but also directly relevant to the needs of the industry. Crop consultants should actively participate in these studies to ensure their voices are heard and the publication continues to be a valuable resource for the industry’s growth and success.
New regulations affecting the neonicotinoid class of insecticides address the type of application (soil or foliar), the number of permitted applications to a crop and the total pounds of active ingredient that may be used in a cropping season.
On Jan. 1, 2024, an update to California Code of Regulations went into effect addressing the use of the neonicotinoid class of insecticides on crops grown in California. The updated regulation covers clothianidin, dinotefuran, imidacloprid and thiamethoxam.
The California Department of Pesticide Regulation has stated it has adopted these regulations to protect pollinators from risks of exposure to neonicotinoids in agricultural crops. The updated regulation covers soil and foliar applications of products containing any of the listed active ingredients to certain crops grown in California. The regulation does not cover applications to crops grown in enclosed areas such as greenhouses or which are covered with insect exclusion netting if the conditions stated in the regulations are met. Also exempt are applications to address a local declared emergency to control a declared quarantine pest, a “Section 18” emergency, treatments made to control a quarantine pest, research and development work with authorization from the DPR, and non-agricultural uses.
The regulations address the type of application (soil or foliar), the number of permitted applications to a crop and the total pounds of active ingredient that may be used in a cropping season. These may vary depending on the crop grown so it is extremely important for pest control advisors, growers, and applicators to make themselves aware of the new restrictions. Crop advisors and growers need to be aware reduced rates of application may result in poor insect control or increase the possibility of insecticide resistance development. It is therefore highly recommended that the rate, method of application and timing of these neonicotinoid products be reviewed and discussed prior to use. Detailed information on each crop may be found by contacting a local UCCE crop advisor, the County Agricultural Commissioner’s office or the California Department of Pesticide Regulation at cdpr.ca.gov/docs/enforce/neonicotinoid/neonicotinoid_regulations.htm.
It is the responsibility of the grower and applicator to ensure regulations are followed.
Key points concerning California 2024 neonicotinoid regulations:
Updated regulations affecting the use of neonicotinoid insecticides go into effect Jan. 1, 2024.
The updated regulations address the potential impact of neonicotinoids on pollinator insects.
The updated regulations will be placed on application timing, amount of active ingredient and number of applications per year.
It will be the responsibility of the grower and the applicator to ensure the updated regulations are met.
California Department of Pesticide Regulation, County Agricultural Commissioners, UCCE and California Licensed Pest Control Advisors will be responsible for educating growers and applicators on complying with the updated regulations.
Growers and applicators need to review application rates and timing to prevent poor pest control or increased insecticide resistance.
‘The only neonicotinoids affected by the updated regulations are imidacloprid, clothianidin, dinotefuran and thiamethoxam.’
Figure 1. Canker caused by Phytophthora syringae at a pruning wound. Infection shows profuse gumming near the canker (photo by A. Hernandez.)
The relentless storms of 2023 set new precipitation records for California and caused widespread local flooding. “Atmospheric rivers,” or major rainstorms, between December and March and the mild temperatures that extended into spring and summer created optimal conditions that led to an unprecedented outbreak of aerial Phytophthora caused by Phytophthora syringae. Almond orchards with severe outbreaks showed numerous trees with branch dieback and cankers with profuse gumming in the upper scaffold branches of the tree. Infection commonly initiated on lateral shoots and progressed into major limbs or scaffold branches where the abundant gumming was produced. The disease was detected as early as mid-February in Fresno County and reported statewide by early summer 2023.
Almond growers should be prepared to respond to the possibility of a recurring outbreak of aerial Phytophthora. This article provides insights about the disease symptoms, the pathogen biology, as well as some management guidelines for this relatively rare but serious disease of almond.
Phytophthora syringae has been associated traditionally with aerial Phytophthora cankers in almond, also known as Phytophthora pruning wound cankers (PPWC). PPWC is characterized by cankers and profuse gumming developing at pruning wounds on branches. The disease has been recorded sporadically during wet years in almond orchards in California and can severely damage an orchard when conditions are favorable.
Early reports of PPWC date back to 1982 when the disease affected almond orchards throughout the Central Valley of California (Bostock and Doster 1985). PPWC was also commonly observed in the late 1990s and early 2000s (Greg Browne, personnel communication). High incidence of the disease generally has been correlated with heavy rainfalls typical of El Niño years such as 1982-83 and 1997-98 in California. The 2023 outbreak of aerial Phytophthora, which followed atmospheric river events, indicated inoculum of P. syringae remains abundantly present in almond orchards in California and that periodic disease outbreaks can occur when conditions are favorable. This recent outbreak also indicated the ability of this pathogen to attack young shoots of almond trees in the absence of pruning wounds. This aspect of the disease biology represents new findings for California, and a detailed description of the various symptoms associated with P. syringae is provided.
Aside from almonds, pruning wound cankers caused by P. syringae have been reported on apricots and French prunes in California (Doster and Bostock 1988d). The pathogen is also known to cause crown and collar rot of several stone fruit (including almond) and is a major cause of citrus brown rot of fruit in California (Adaskaveg et al. 2014). Aerial fruit rot of peaches and apple caused by P. syringae have been reported in Italy and England, respectively.
Figure 1. Canker caused by Phytophthora syringae at a pruning wound. Infection shows profuse gumming near the canker (photo by A. Hernandez.)
Disease Symptoms
Aerial Phytophthora cankers associated with P. syringae have been usually associated with pruning cuts (Figure 1) including thinning cuts made during the fall, winter or early spring. In 2023, shoot infections in the absence of pruning wounds were particularly common in almond orchards.
Figure 2. Early sign of gumming and shoot infection by Phytophthora syringae (photos by A. Hernandez and J. Adaskaveg.)
Early shoot infection causes dieback and moderate gumming (Figure 2) occurs from underlying necrotic tissues. Eventually, shoots dieback, and the disease progresses into larger branches, with new infections developing at the junction between a branch and the dead shoot. A canker is then formed, and additional gumming is produced (Figure 3). Gum balls in branches vary in color from bright amber to gold, and reddish-brown to burgundy red (Figure 4). The unique gumming appearance associated with P. syringae infections is a distinguishing feature that can help with field diagnosis of the disease.
Figure 3. Shoot infections by Phytophthora syringae moving into scaffold branches and producing new gumming and cankers (photos by A. Hernandez, F. Trouillas and J. Adaskaveg.)
In branches, cankers generally expand quickly from an infection site (pruning wounds or shoot junction), extending to more than 6 inches within three weeks of infection. Length of cankers in branches can reach up to 16 inches or longer. Removal of the outer bark reveals distinct concentric canker margins of alternating light-brown to brown tissue (Figure 5). Infections are generally restricted to the cambium tissue and do not cause internal wood discoloration as seen with some fungal cankers. Dieback of branches can be observed in orchards; however, trees typically do not die due to infections with P. syringae. During the 2023 outbreak, disease incidence (number of trees affected) in orchards varied from 10% to 75%, although severity may differ between different sections of an orchard. Susceptible cultivars include Nonpareil, Shasta, Aldrich, Monterey and Bennett-Hickman.
Figure 4. Bright amber to gold, and reddish-brown to burgundy red gum balls in almond branches resulting from infections by Phytophthora syringae (photos by A. Hernandez.)
PPWC and the aerial Phytophthora are not to be confused with the Perennial Phytophthora Canker disease of almond, primarily caused by P. cactorum and P. citricola. Both diseases can cause aerial infections of almond trees, however P. syringae infections are annual, nonlethal to entire trees and associated with pruning wounds or young shoots. In contrast, perennial Phytophthora cankers are typically year-round, lethal to trees, and associated with water holding pockets and cracks at the tree crotch. Additionally, cankers caused by P. syringae can easily be mistaken for common fungal canker diseases affecting almond trees, such as Ceratocystis canker caused by Ceratocystis destructans and band canker caused by Botryosphaeriaceae fungi.
Figure 5. A canker developing in the bark of almond with zonate margins (photo by A. Hernandez.)
Phytophthora Species Biology
Phytophthora species were once considered fungi but are now classified in a separate kingdom, the Stramenopila, in the phylum Oomycota. Phytophthora species are soil-inhabiting plant pathogens that thrive under wet environmental conditions, hence the common name of “water molds” is often used to describe these organisms. Diseases caused by Phytophthora pathogens result in devastating losses to agriculture crops and native forests. Phytophthora species have a cell wall composition, cytoplasmic organelles and biochemical processes that are different than that of true fungi. Thus, fungicides that target true fungi are ineffective for the management of Phytophthora species. Phytophthora species can survive dry periods through the formation of oospores (sexual spores) or chlamydospores (asexual spores). These are hardy, thick-walled spores tolerant of unfavorable environmental conditions (i.e., drought, heat) and serve as survival structures for Phytophthora species. Under favorable environmental conditions (i.e., wet, cool) these survival structures can germinate to develop sporangia (sac-like structures) that form and release zoospores (asexual swimming spores). Oospores, chlamydospores, sporangia and zoospores can all serve as infective propagules that cause diseases. Zoospore formation and release are favored when there is standing water in the orchard as a result of flooding, overwatering or significant rain events. Certain Phytophthora species may produce up to 68 zoospores from a single sporangium. Thus, under favorable conditions, zoospore inoculum can reach very high levels in orchards and increase the risk for disease to occur.
Disease Development in Orchards
Disease outbreaks of aerial Phytophthora caused by P. syringae are sporadic and usually are favored by cool and wet environmental conditions. Pruning wounds made during fall, winter or spring can be susceptible to infection when conditions are cool and rainy. Under these environments, shoot infection also can occur. In particular, the atmospheric river events of 2023 appear to have greatly contributed to shoot infection, although the exact mechanism of such infection is unknown. Similarly, the mechanism of inoculum dispersal to pruning wounds is not known. However, it is presumed oospores and eventually zoospores and sporangia of P. syringae occurring in the soil and leaf litter are blown up into the tree canopy during high winds and heavy rain events, where they can then infect fresh pruning wounds and young shoots. Windrowing of harvested almonds using air-blowers in orchards creates substantial soil dust clouds that coat the surfaces of almond trees including shoots and branches. The soil dust carries the resting spores of P. syringae and essentially inoculate the tree with subsequent infections occurring during rain or any prolonged wetness events.
Almond pruning wounds can remain susceptible to infection by P. syringae for about four weeks after pruning (Doster and Bostock 1988c). Following infection, canker expansion occurs relatively quickly and is favored by cool temperatures. The optimum temperature of P. syringae is 59 to 68 degrees F (15 to 20 degrees C). Canker expansion slows down as temperatures increase in late spring and eventually stops completely above 73 degrees F (23 degrees C). Mycelium of the pathogen dies under hot summer temperatures. In the fall, fallen leaves on the almond orchard floor have been found to contain oospores of P. syringae (Doster and Bostock 1988a). The pathogen’s ability to colonize and form oospores in the leaf litter can be a mechanism for increasing and maintaining inoculum loads in the field and may contribute to the spread of P. syringae to other parts of the orchard or to neighboring orchards. The pathogen has a large host range occurring on plants of 24 genera in 14 families including lilac and commonly on plants in the family Rosaceae.
Disease Management
As mentioned previously, pruning wounds can remain susceptible to P. syringae infection for about four weeks after pruning if wounds are left unprotected. Previous research showed the application of a phosphonate product (i.e., fosetyl-Al1) directly to fresh pruning wounds was effective at preventing infection by P. syringae for at least four weeks following pruning (Doster and Bostock 1988b). Cupric hydroxide was less effective than phosphonate and caused some phytotoxicity at the pruning wound, resulting in clear gumming, xylem discoloration, excessive inner bark dieback and abnormal lignification (Doster and Bostock 1988b).
Curative management strategies to control aerial Phytophthora may involve chemical treatments of systemic fungicides. These include potassium phosphite or other phosphonate compounds (e.g., Kphite®7LP, Fungi-Phite®) applied as foliar treatments or by chemigation, and mefenoxam (Ridomil Gold® SL) applied by chemigation. Mefenoxam provides protection by directly targeting the pathogen and disrupting certain biosynthetic pathways. Phosphite products provide plant protection through the induction of host plant defense against plant pathogens and by direct inhibition of growth. When environmental conditions (e.g., atmospheric rivers, flooding) are favorable to aerial Phytophthora outbreaks, preventive applications of a phosphite compound may be considered. High resistance to phosphonate fungicides, however, has been reported in P. syringae populations occurring on citrus but not yet on almond. Systemic fungicides may be applied as chemigation treatments as early as mid-March and no later than mid-May in California in order to overlap with the timing of root flush of almond trees. Foliar applications with phosphonate fungicides can also be effective because the fungicide is systemic with both upward and downward mobility in the tree (i.e., ambimobile). Applications after May are less effective at controlling P. syringae since the disease and tree damage has already occurred and mycelium of the pathogen will die naturally with warm summer temperatures.
Recently, the new fungicide oxathiapiprolin (Orondis®) was shown effective and is labeled only for chemigation or soil application for the control of Phytophthora diseases of almond. This product may be used following flooding of an orchard, and before or shortly after planting almond trees to reduce soil inoculum sources and risks of Phytophthora root and crown rot infection. Orondis® also has shown moderate systemic activity that can mitigate infection of the lower trunk. Nevertheless, oxathiapiprolin is not effective at managing aerial Phytophthora as the product is registered for soil applications and does not translocate above the tree crotch at registered labeled rates.
Aside from fungicides, certain cultural practices can be implemented to manage aerial Phytophthora. Indeed, the disease can be avoided by pruning outside of rainy periods. Lignification and healing of pruning wounds occurs naturally but it is faster under warm environmental conditions. Accordingly, best timing for pruning is after harvest in the early fall or during dry weather in the late winter or early spring when warmer conditions favor the rapid healing of pruning wounds. There are no cultivars completely resistant or tolerant to P. Syringae; however, susceptibility trials conducted in 1984-86 showed the cultivar Ripon was the least susceptible when compared to Nonpareil, Butte, Mission, Fritz, Carmel, Ne Plus Ultra and Thompson cultivars.
Disclaimer: Mentioning of any active ingredients or products is not an endorsement or recommendation. All chemicals must be applied following the chemical label, local and federal regulations. Please check with your PCA to confirm rates and site-specific restrictions. The authors are not liable for any damage from use or misuse.
Note: Fosetyl-Al is currently registered for use in nonbearing almond trees only. Please check with your PCA to confirm rates and site-specific restrictions. More information regarding chemicals used to control Phytophthora diseases can be found at the UC IPM website at http://ipm.ucanr.edu/?src=www2.
References
Adaskaveg, J.E., Hao, W., and Förster, H., 2015. Postharvest strategies for managing Phytophthora brown rot of citrus using potassium phosphite in combination with heat treatments. Plant Dis. 99:1477-1482.
Bostock, R.M., and Doster, M.A. 1985. Association of Phytophthora syringae with pruning wound cankers of almond trees. Plant Dis. 69:568-571.
Doster, M.A., and Bostock, R.M. 1988a. Incidence, distribution, and development of pruning wound cankers caused by Phytophthora syringae in almond orchards in California. Phytopathology 78:468-472.
Doster, M.A., and Bostock, R. M. 1988b. Chemical protection of almond pruning wounds from infection by Phytophthora syringae. Plant Dis. 72:492-494.
Doster, M.A., and Bostock, R.M. 1988c. Effects of low temperature on resistance of almond trees to Phytophthora pruning wound cankers in relation to lignin and suberin formation in wounded bark tissue. Phytopathology 78:478-483.
Doster, M.A., and Bostock, R.M. 1988d. Susceptibility of almond cultivars and stone fruit species to pruning wound cankers caused by Phytophthora syringae. Plant Dis. 72:490-492.
Hao, W., Miles, T. D., Martin, F. N., Browne, G. T., Förster, H., Adaskaveg, J. E. 2018. Temporal occurrence and niche preferences of Phytophthora spp. causing brown rot of citrus in the Central Valley of California. Phytopathology 108:384-39.
Hao, W., Förster, H., Adaskaveg, J. E. 2021. Resistance to potassium phosphite in Phytophthora species causing citrus brown rot and integrated practices for management of resistant isolates. Plant Dis. 105: 972-977.
O’Fallon, C., Belisle, R. J., Hao, W., Förster, H., Adaskaveg, J. E. 2022. Systemic movement of selected Oomycota fungicides effective against Phytophthora root and crown rots of almond and cherry. Phytopathology (abstr.) 112 (S3): 146
O’Fallon, C., Hao, W., Förster, H., Browne, G. T., Adaskaveg, J. E. 2023. Baseline sensitivities of new Oomycota fungicides for registration on almond for managing Phytophthora root and crown rots. Phytopathology (abstr.) 113 (S3): 24
Figure 1. Head rot symptoms start as yellow spots and then turn brown and black (all photos courtesy Y. Wang.)
Broccoli head rot, also known as pin rot, continues to increase in the Salinas Valley, especially in fall broccoli production. Two types of head rot, bacterial head rot and Alternaria head rot, are affecting broccoli (Koike 2010). Here we focus on Alternaria head rot caused by the fungi Alternaria spp.
Head Rot Symptoms
All aboveground parts of broccoli are subject to infection including heads and leaves. Head rot symptoms start as yellow spots and then turn brown and black (Figure 1).
Figure 1. Head rot symptoms start as yellow spots and then turn brown and black (all photos courtesy Y. Wang.)
The infection can spread from buds to stems (Figure 2).
Figure 2. The infection can spread from buds to stems.
With secondary bacteria or fungi infection, further decay occurs. The initial yellow spots resemble brown bead (Figure 3), a broccoli disorder that can potentially be caused by excessive temperature, poor growth or nutrient and water deficiency. However, the brown bead doesn’t rot the stem, and no sign of fungi is presented on the buds. For uncertain cases, scraping the buds to see if the stem rot or fungi are presented is a useful technique. Leaf spot symptoms start as small yellow spots on the old leaves and then form dark, concentrical rings like a target (Figure 4). The old spots may become brittle and split open or fall out as shot holes. The high number of leaf spots per plant indicates a higher disease pressure and could be a signal for fungicide application.
Figure 3. Brown bead, a broccoli disorder.
Management Options
The disease is favored by prolonged wetness from rain, dew and fog. The wetness, a thin layer of water, is required for fungal spore germination. In addition, fungal spores are spread by winds and splashing water. Cultural practices to promote leaf drying or prevent leaf wetness may reduce disease severity. Some growers have seen the benefits of using drip irrigation instead of overhead irrigation to avoid wetting the foliage. An early harvest before rainfall could also reduce disease risk. Variety effects on disease tolerance play a role. Lumpy broccoli heads tend to accumulate water which may further weaken the plant tissues and become a suitable target for the pathogens. Finally, there are a number of fungicides that have activity against the disease. Preventative fungicide applications should be considered for wet weather that is favored by the disease.
Figure 4. Leaf spot symptoms start as small yellow spots on the old leaves and then form dark, concentrical rings like a target.
Research Update: Fungicide Evaluation
This study was conducted to evaluate some new and common fungicides in fall broccoli to support the growers and ag industry.
One fungicide trial was conducted in a commercial broccoli field to test the efficacy of select fungicides for controlling broccoli head rot in fall 2023. Broccoli ‘Centennial’ was direct-seeded on July 27, 2023. Seven fungicide treatments and a nontreated control were arranged in a randomized complete block design with four replications. Each plot consisted of two seedlines of broccoli 30-ft long on 40-inch-wide beds. On each side of the plot was a nontreated guard bed. Treatments were applied with a CO2-pressurized backpack sprayer calibrated to deliver 35 gpa at 30 psi using double TeeJet 8004E flat fan nozzles. Fungicide applications were made on October 4 and October 16. All treatments were applied with non-ionic surfactant Dyne-Amic 0.08% v/v. Alternaria head rot incidence was evaluated at harvest on October 23. Disease incidence was expressed as the percentage of the number of plants with Alternaria head rot in the total number of plants within the middle 15 ft of the plot. Data were analyzed using analysis of variance (ANOVA) and the Tukey test to separate means at P<0.05. The total rainfall received one month before harvest was 0.57 inches. The average, minimum and maximum temperatures were 62 degrees F, 53 degrees F and 75 degrees F, respectively.
Table 1
The disease pressure in this trial area was low with nontreated control having 14.0% head rot (Table 1). However, significant differences occurred among treatments for the % Alternaria head rot. All treatments reduced % Alternaria head rot numerically, while Pydiflumetofen+Fludioxonil, Azoxystrobin, Fluxapyroxad+Pyraclostrobin, Fluopyram+Trifloxystrobin and Pyraclostrobin had significantly lower % Alternaria head rot than nontreated control. And they had statistically similar % Alternaria head rot. These results also showed single FRAC 11, premixes with FRAC 7 and 11, and premixes with FRAC 7 and 12 provided good control of Alternaria head rot. Single FRAC 7 provided fair control of Alternaria head rot.
Thanks to the cooperating growers and PCAs for assisting the trial. Thanks to agrochemical companies for funding and the technical assistance from Carlos Rodriguez.
References
Koike, S. T. 2010. Looking ahead: head rot can be issue for winter and early spring broccoli. Salinas Valley Agriculture blog. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=3861
Olives produce numerous small flowers (a) on panicles (b). Each panicle contains 12 to 20 flowers (b). Perfect flowers contain two anthers and a pistil in the center (c) (photos by E. Andrews, illustration by S. Hishinuma.)
Olive orchards entering an ‘off’ year in 2024 may benefit from pre-bloom foliar boron applications to support reproduction and yield. Because the 2023 California olive crop varied widely both within and between olive-growing regions, the value of B applications should be considered at the individual orchard level. For example, in the southern San Joaquin Valley, the 2023 ‘Manzanillo’ table olive crop was off due to the high temperatures at bloom whereas many oil cultivars in the region were unaffected by the heat and had heavy production. Those orchards that had a heavy ‘on’ crop in 2023 may benefit from pre-bloom B application in the 2024 season.
B is an essential micronutrient for plant growth and reproduction. B deficiency affects plant reproduction by reducing pollen viability and germination and limiting pollen tube growth. Deficiency also limits the proportion of flowers that set fruit and reduces the retention of developing fruit. The influence of B deficiency on multiple stages of reproduction may negatively impact yield. B also plays a role in vegetative growth and metabolism, ensuring cell wall and membrane integrity and facilitating sugar transport and cell division. Because it plays a crucial role in reproduction, B is translocated from vegetative tissues to reproductive tissues, resulting in higher concentrations of the nutrient in reproductive organs than leaves. Due to this high demand, reproductive B deficiency can occur even when vegetative B and available soil B are sufficient.
Figure 1. Olives produce numerous small flowers (a) on panicles (b). Each panicle contains 12 to 20 flowers (b). Perfect flowers contain two anthers and a pistil in the center (c) (photos by E. Andrews, illustration by S. Hishinuma.)
Benefits of Boron
Studies conducted across numerous global olive-growing regions demonstrate the beneficial effects of foliar B application on yield, particularly in advance of an off crop. The influence of B application on productivity in olive orchards may relate to increases in photosynthesis, an increase in the number of perfect flowers (those with both male and female reproductive parts) (Figure 1) and an increase in pollen viability, or pollen tube growth. Olives are considered andromonoecious, a reproductive strategy in which plants bear both hermaphroditic (perfect) flowers and male flowers. Stress prior to bloom may cause pistil abscission in a fraction of buds resulting in a higher percentage of male flowers. Several research studies have demonstrated pre-bloom foliar B application can increase the percent of perfect flowers on trees, thus increasing the number of flowers capable of producing fruit. In olive, B is readily mobilized from both young and old vegetative growth to support flower and fruit production; therefore, a portion of B applied throughout the year may be utilized to support reproductive processes. During the pre-bloom season, however, cool temperatures and the corresponding reduced physiological activity may limit the uptake and translocation of B in olive. Additionally, flowers are not as strong a B sink as fruit; therefore, the pre-bloom foliar application may render the micronutrient available at a short-lived yet critical time in crop development.
Both oil olives and ‘Manzanillo’ table olives have been shown to benefit from foliar B applications. For example, ‘Arbequina’ receiving pre-bloom foliar application of B exhibited increased bloom and a 27% increase in yield in an off year. In the ‘Arbequina’ study, no value of B was observed in an on year, and B was found to have no effect on vegetative growth. In another study, B applications to ‘Frantoio’ resulted in increased concentration of chlorophyll and soluble sugars as well as changes in the profile of endogenous plant growth regulators within the leaves. In California, pre-bloom B applications on ‘Manzanillo’ resulted in increased percentage of perfect flowers and improved fruit set and yield, particularly during an off year.
Recommended Application
The recommended foliar B concentration for olives ranges from 19 to 150 ppm. Values below 14 ppm B may result in B deficiency, whereas values above 185 ppm may result in B toxicity. A foliar nutrient analysis only provides a snapshot of the status of the plant at the time of leaf collection; however, low B status of leaves has been found to correlate well with symptoms of deficiency. Symptoms of B deficiency in olive include dead leaf tips with a characteristic yellow band and green leaf base as well as twig and limb dieback (Figure 2). B deficiency may first become apparent in the meristems, the growing tips of shoots. B deficiency may also result in misshapen and defective fruit (Figure 2), low fruit set and premature fruit drop. The value of B application for improved fruit set is not limited to orchards with visual symptoms of B deficiency or foliar B levels below the recommended range. In fact, the numerous research studies that demonstrate the value of pre-bloom foliar B applications for enhanced fruit set and yield were conducted in orchards with no B deficiency. Based on these findings, foliar analysis alone may not be a useful predictor of benefits from pre-bloom foliar B application.
Figure 2. Symptoms of boron deficiency in olive include dead leaf tips with a characteristic yellow band and a green leaf base (a) and misshapen fruit (b) (photos courtesy J. Connell.)
B is typically introduced to orchards either as a solid mineral broadcast on the soil surface, or in solution as a foliar spray. The pre-bloom foliar application is designed to specifically enhance fruit set and yield and should be applied three weeks prior to bloom. B is generally sold as borax, sodium borate, sodium tetraborate, boric acid, or Solubor® (Table 1). The B content varies between formulations; therefore, all calculations should be based on the equivalents of active ingredient (i.e., pounds of B). For example, for soil-applied B in olive, 5 to 10 lbs/acre B is broadcast, which equates to approximately 45 to 49 lbs/acre borax (11% B) or 24 to 48 lbs/acre Solubor® (20.5% B). In California, foliar application of B three weeks prior to ‘Manzanillo’ bloom, particularly in off years, at rates of 1 or 2 lb./acre Solubor® in a 100 gallon/acre (246 or 491 mg/L B at 935 L/hectare) was demonstrated to improve yield by approximately 30%. The baseline B level in this California study site was 16 ppm B, a level just below the established critical level, but high enough to avoid deficiency symptoms.
The value of B applications on orchard health and economic return varies based on the status of the alternate bearing cycle in the year of application, the baseline B status of the tree and soil, and other climate factors that may influence yield. Plants have a narrow range between B deficiency and toxicity. Be sure to read the product label carefully to avoid over-application and conduct annual leaf tissue analyses to gather baseline information on the B status of orchards. More information on fertilizer rates for olives and other California crops may be found on the CDFA FREP California Crop Fertilization Guidelines website at cdfa.ca.gov/is/ffldrs/frep/FertilizationGuidelines/.
Because of their comprehensive knowledge in soil, water and nutrient management, crop consultants have been asked to play a role in helping California growers meet requirements of the Irrigated Lands Regulatory Program (photo by Vicky Boyd.)
As water quality regulations intensify for California growers, the industry has drawn attention to crop consultants as a source of trusted knowledge and advice. Rigorous certifications, such as the Western Region Certified Crop Adviser (WRCCA), ensure the most qualified agricultural professionals are available to support growers in improving their farming operations through efficient practices and resource use. Because of their comprehensive knowledge in soil, water and nutrient management, crop consultants have been asked to play a role in helping California growers meet requirements of the Irrigated Lands Regulatory Program (ILRP).
Precedential Water Quality Requirements for Growers
ILRP regulates discharges such as nitrate from irrigated agriculture to protect surface and groundwater quality. ILRP covers over 6 million acres of irrigated lands in growing regions across California. Due to the diversity in production systems and water quality impairments across the State, regulations are generally handled on a regional basis. However, some reporting requirements set by the State Water Resources Control Board (SWRCB) serve as precedential requirements across all regions.
In 2018, SWRCB amended the waste discharge requirements for the East San Joaquin River Watershed. This ruling is referred to as the Eastern San Joaquin (ESJ) Order. SWRCB designated portions of the ESJ Order as precedential and directed the Regional Water Boards to revise their programs to be consistent with the precedential requirements. So far, almost all Regional Water Boards have updated their regulatory language to reflect the precedential requirements.
The precedential regulations include the requirement for all growers to complete Irrigation and Nitrogen Management Plans (INMP) and submit summary data to a third-party coalition or the Regional Water Board.
INMP reporting requirements serve two main purposes: The first is to help growers project the total amount of N a given crop will require over the season. Such planning can increase application efficiency and reduce the loss of N to surface and groundwater. Second, the data made available through the summary reports enable third-party coalitions to analyze the range of N application rates for each crop in the region. This allows the coalitions to identify any parcels that may be outliers and implement follow-up action to help reduce overapplication.
There are several trainings and resources available to crop consultants that cover the information needed to prepare a detailed and accurate INMP including the University of California’s Nitrogen Management Training for Crop Consultants.
Role of Crop Consultants
The precedential requirements have increased the need for agricultural professionals trained in irrigation and nutrient management practices and technologies. CCAs have been identified to fill this need along with certified professional soil scientists, agronomists and agriculture irrigation specialists. Being familiar with the precedential requirements and completing INMP worksheets and summary reports adds value to your professional toolkit.
Additionally, growers in your region may be required to have INMPs certified by a specialist in irrigation and N management. The Regional Water Boards have discretion on requiring if all growers’ INMPs must be certified, or just a subset of growers, based on a risk categorization such as the low/high vulnerability area distinction. Currently, the Central Valley and Los Angeles Regional Boards require certification of plans for parcels located in high vulnerability areas.
To certify INMPs for growers in these regions, you must hold one of the following certifications:
By signing off on a grower’s INMP, you are certifying the INMP was prepared under your direction and supervision and that the data reported is, to the best of your knowledge, accurate and complete. Additionally, you are certifying that you used sound irrigation and N management planning practices to develop your recommendations and that the recommendations are informed by applicable agronomic training.
As a certifier, you are not responsible for any damages, loss or liability arising from subsequent implementation of the INMP by the grower in a manner inconsistent with INMP’s recommendations. The certification does not create any liability or claims for environmental violations.
Nitrogen Management Course and Specialty Certification for Crop Consultants
There are several trainings and resources available to crop consultants that cover the information needed to prepare a detailed and accurate INMP including the University of California’s Nitrogen Management Training for Crop Consultants.
The self-paced course covers N and irrigation management practices that reduce environmental impacts while maintaining crop productivity. Participants receive access to online videos covering a variety of topics, including N cycling, sources, budgeting, dynamics in California cropping systems, the environmental impacts of N loss, irrigation management and barriers to adoption of environmental practices.
The course offers 10 hours of CCA continuing education credits. While the course is designed for CCAs, anyone interested in learning more about N and irrigation management in California agriculture is welcome to participate. The course is open for enrollment through May 31, 2024 at https://ucanr.edu/sites/nitrogencourse/.
The course was created to provide CCAs with the specialized training and education necessary to obtain the California Nitrogen Management Specialty Certification (CA-NSp). The CA-NSp is for California-based CCAs who provide N management planning services to their clients and are interested in certifying INMPs. CCAs must pass the exam to obtain the specialty certification. After passing the exam, specialists must maintain their certification by meeting the continuing education requirements set by the CCA Program.
Individuals that participated in CDFA’s Nitrogen Management Training for CCAs prior to Oct. 1, 2020 were automatically awarded the specialty certification.
CDFA Irrigation and Nitrogen Management Training Program
CDFA’s FREP also offers a training that covers the basics of irrigation and N management and provides step-by-step instructions in completing INMP worksheets and summary reports.
The self-paced course and accompanying workbook were designed for growers required to complete INMPs and interested in self-certification. However, the training workbook is also available to crop consultants developing and certifying plans for growers. The digital workbook covers all the information provided in the training and includes exercises and additional resources (https://www.cdfa.ca.gov/is/ffldrs/frep/training.html).
Supporting Growers into the Future
As regulatory pressure increases, the demand for trained professionals will continue to rise. Taking part in a certification program like WRCCA helps demonstrate to growers that you have the knowledge and experience to provide sound advice in irrigation and nutrient management practices that will help them meet regulatory requirements. As crop consultants, it is important to stay up to date on the latest research and technology so we can support growers as they face the challenges of balancing profitability with environmental stewardship.
CDFA’s FREP provides funding for research, education and outreach projects focused on advancing agricultural nutrient and irrigation management practices. To receive updates on current and completed projects, FREP’s grant cycle and relevant irrigation and nutrient management events, subscribe to the FREP newsletter at www.cdfa.ca.gov/subscriptions/.
