Figure 1. Early symptoms of red leaf blotch include small, pale yellowish spots or blotches that affect both sides of the leaves (all photos by A. Hernandez and F. Trouillas.)
Red leaf blotch (RLB), caused by the fungal pathogen Polystigma amygdalinum, is one of the most important leaf diseases currently affecting almond trees in the Mediterranean basin, particularly in Spain, and regions of the Middle East. In late May 2024, unusual symptoms on leaves, including yellow spots and orange to dark red-brown blotches, were detected in an almond orchard (Nonpareil, Monterey and Fritz) on the border of Merced and Madera counties. The disease has since been observed in Madera, Merced, San Joaquin and Stanislaus Counties, suggesting it is somewhat widespread in the Northern San Joaquin Valley. Following field sampling as well as morphological and DNA/PCR analyses, our laboratory confirmed the detection of P. amygdalinum from symptomatic leaves. This is the first detection of P. amygdalinum from California almond, and the pest has formally been confirmed as being present in the state by both CDFA and USDA. Growers and PCAs should be on the lookout for RLB as it is new to California and a serious disease of almond.
Disease Symptoms and Biology
Symptoms of RLB initiate as small, pale yellowish spots or blotches that affect both sides of the leaves (Fig. 1). As the disease progresses, the blotches grow larger (1 to 2 cm) and turn yellow-orange with a reddish-brown center (Fig. 2). At advanced stages of disease development, leaves become necrotic, curl and drop prematurely. Mainly the leaves are affected, and premature defoliation of trees can occur, thus decreasing the photosynthetic capacity of the tree during the current and following growing season, leading to a general decrease in yield.
Figure 2. Advanced symptoms of red leaf blotch include larger, yellow-orange blotches (1 to 2 cm) that turn reddish-brown in their center.
The disease is monocyclic, with only one primary infection cycle. The primary inoculum are ascospores that form in perithecia (sexual fruiting bodies) on fallen infected leaves from the previous growing season. Infection occurs after petal fall when young leaves emerge and spring rains occur. Rain is essential for the release and dispersion of ascospores from perithecia. The disease may not be noticed before late April to mid-May as infection remains latent for approximately 35 to 40 days. Infected leaves develop small yellow blotches that expand and become orangish to reddish-brown, with variable shapes and sizes, as the fungus colonizes more leaf tissue. During spring/summer, leaves contain the pycnidia (asexual fruiting bodies) of the fungus, which produce filiform conidia. These asexual spores do not cause new infection on leaves. Infection of leaves decrease drastically after June and with high summer temperatures. Rain combined with mild temperatures in spring and early summer generally lead to higher disease incidence.
Disease Management
Research and experience in Spain where RLB is more common have shown one preventive fungicide application at petal fall and two additional applications at two and five weeks after petal fall if rains persist are effective at controlling the disease (this exact timing is not critical but depends on the occurrence of rainfall.) This means fungicide applications and timings to control other common diseases of almond in California, such as shot hole or anthracnose, will likely also control this pathogen. Researchers in Spain also have shown FRAC groups 7, 11, M3, M4 and some FRAC3 chemistries are most effective. Cultural practices focused on eliminating the primary inoculum of infected fallen leaves also can help mitigate the disease. These consist of removing leaf litter or applying urea to accelerate its decomposition. However, such strategies are only effective when applied over a wide area. Fungicides applied during bloom and after symptoms are visible are not effective.
If you suspect that you have this new disease in your almond orchard, please contact your local UCCE farm advisor.
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.
References
López-Moral, A., Agustí-Brisach, C., Ruiz-Prados, M.D., Lovera, M., Luque, F., Arquero, O. and Trapero, A., 2023. Biological and urea treatments reduce the primary inoculum of red leaf blotch of almond caused by Polystigma amygdalinum. Plant Disease, 107(7), pp.2088-2095.
Torguet, L. 2022. El inicio del fin de la mancha ocre (Polystigma amygdalinum) como enfermedad clave del almendro. XIV Jornada Del Almendro. Les Borges Blanques, 22 septiembre 2022. IRTA.
Torguet, L., Maldonado, M., Miarnau, X. 2019. Importancia y control de las enfermedades en el cultivo del almendro. Agricultura 1026: 72-77.
Torguet, L., Zazurca, L., Martinez, G., Pons-Solé, G., Luque, J., Miarnau, X. 2022. Evaluation of fungicides and application strategies for the management of the red leaf blotch disease of almond. Horticulture 8, 50.
The Crop Consultant Conference will take place on September 25 and 26 at the Visalia Convention Center in Visalia, Calif. (all photos by K. Platts.)
As the agriculture industry continues to evolve, staying informed and connected is more critical than ever. The Crop Consultant Conference, hosted by JCS Marketing Inc., is rapidly becoming a must-attend event for professionals in the field. With growing attendance, an increasing number of exhibits, and a surge in sponsorships, this year’s conference promises to be the most impactful yet.
Growing Attendance and Exhibits Year after year, the Crop Consultant Conference has seen a significant increase in the number of attendees. This surge reflects the conference’s reputation as a leading platform for learning, networking and showcasing the latest advancements in crop consulting. This year, we expect record-breaking attendance as more professionals recognize the value of participating in this pivotal event.
The exhibit hall will feature an expanded array of booths from top industry players, providing attendees with firsthand access to innovative products, services and technologies that are shaping the future of agriculture. From cutting-edge equipment to the latest in crop management solutions, the exhibit hall will be a hub of activity and discovery.
Enhanced CE Management with Online Courses Understanding the importance of continuing education (CE) for crop consultants, JCS Marketing Inc. has developed an online CE manager to streamline the process for attendees. This user-friendly platform allows participants to manage their course schedules, track credits and ensure they meet their professional development requirements seamlessly.
To provide comprehensive educational opportunities, JCS Marketing Inc. is offering 11 online credits before the conference, 9 live credits during the event and an additional 20+ credits available online after the conference. This extensive offering ensures attendees can fulfill all their CE requirements in one place, maximizing both their time and investment.
Record Attendance and Sponsorships Expected The growing success of the Crop Consultant Conference is mirrored by the increasing interest from sponsors. This year’s event is set to feature more sponsors than ever before, each eager to connect with the highly engaged audience the conference attracts. Sponsors recognize the value of aligning with a conference that draws the best and brightest in the industry, providing unparalleled opportunities for brand exposure and relationship building.
Unmatched Networking Opportunities Networking is a cornerstone of the Crop Consultant Conference, and this year, we’ve expanded our offerings to include more networking parties than ever before. These events provide attendees with invaluable opportunities to connect with peers, share insights and forge lasting professional relationships. Whether you’re looking to collaborate on new projects, exchange ideas or simply catch up with old friends, the networking parties are not to be missed.
The exhibit hall will feature an expanded array of booths from top industry players.
Don’t Miss Out With its growing attendance, enhanced educational offerings and increased sponsorship, the Crop Consultant Conference is poised to be the premier event of the year for agricultural professionals. Whether you’re a seasoned consultant or new to the field, this conference offers a wealth of opportunities to learn, connect and grow.
Join us at the Crop Consultant Conference on September 25 and 26 at the Visalia Convention Center in Visalia, Calif. and be part of a vibrant community dedicated to advancing the future of crop consulting. Secure your spot today and ensure you don’t miss out on the premier event of the year.
Barn owls (Tyto alba) are invaluable allies for growers seeking effective, sustainable and natural pest management against gophers, voles and field mice (photo courtesy N. Davis.)
Barn owls (Tyto alba) are birds of prey known for their heart-shaped faces and eerie, yet captivating, screeches in the night. These nocturnal hunters play a crucial role in ecosystems worldwide by helping to control rodent populations, making them invaluable allies for growers seeking effective, sustainable and natural pest management against gophers, voles and field mice.
One of the most striking features of barn owls is their exceptional hearing and vision, which allow them to hunt effectively in low light conditions. Their keen sense of hearing is aided by facial discs that funnel sound to their asymmetrical ears, enabling them to pinpoint the slightest rustle of prey in the darkness. Additionally, their feathers are uniquely designed to muffle the sound of their flight, allowing them to approach prey silently, making them highly efficient hunters.
The Gopher Problem: A Closer Look
Gophers, along with voles and field mice, are notorious for their extensive tunneling activities, which can cause significant damage to crops. One of the problematic issues gophers create in row crop farming (i.e., tomatoes) is chewing through subsurface irrigation hoses. These hoses are vital for delivering precise amounts of water to crops, ensuring they receive the moisture needed for optimal growth. When gophers chew through these hoses, it can lead to uneven watering, water wastage and even crop failure. The cost of repairing or replacing damaged irrigation systems can be substantial, adding to the financial burden on growers.
In addition to damaging irrigation systems, gophers pose a severe threat to young almond and pistachio trees. These trees are particularly vulnerable in their early stages of growth when their root systems are not fully developed. Gophers chew through the roots and bark, disrupting the flow of nutrients and water, ultimately leading to the death of the trees. This not only affects the current crop yield but also has long-term implications for the orchard’s productivity. The loss of young trees means additional expenses for replanting and lost time waiting for new trees to mature and start producing.
Traditional Pest Control Methods: Challenges and Drawbacks
Traditionally, growers have relied on methods such as traps and poisons to control gopher populations. While these methods can be somewhat effective, they come with significant drawbacks. The most significant drawback to trapping is the cost of this activity. Trapping requires constant monitoring and maintenance, making them labor-intensive and costly over time. Poisons, well, California doesn’t like us to use them, so the formulations are becoming softer and softer. Moreover, these methods do not address the root of the problem and can lead to a cycle of constant management without achieving a sustainable solution.
Barn Owls: A Sustainable and Effective Solution
Barn owls primarily feed on small mammals such as gophers, voles and field mice, which coincidentally make them ideal for controlling agricultural pests. A single barn owl family can consume up to 60 pounds of rodents in a year. Consultants should consider recommending growers to consider installing barn owl boxes in their fields immediately for several reasons.
Firstly, Barn owls simply kill to survive. No other gopher management method can compete with a barn owl family’s need to eat and properly nourish the two to six owlets in the nesting box. This unique need is what makes barn owls stand out from all other gopher management methods; it’s where their magic lies. Secondly, they save money on irrigation repair and reduce payroll. Thirdly, managing barn owl nesting boxes is easy. It’s like cooking with a crockpot; ‘set it and forget it!’ They require minimal time and money to maintain.
To get barn owls working ASAP, simply install specially designed nesting boxes. After installation, these nesting boxes will attract male barn owls first. After some necessary courting, he will attract a female, and then we’re off to the races. These nesting boxes mimic the natural hollows of trees where barn owls typically nest, providing them with a safe and secure place to raise their young. By installing these boxes, we’re encouraging them to take up residence on the farm and build a community of barn owls that will prey on rodents night after night.
It’s essential to ensure boxes are placed at a height of 10 to 12 feet off the ground (photo courtesy Vineyard Team.)
Installing Barn Owl Boxes
To effectively utilize barn owls for pest control, growers need to install suitable nesting boxes in strategic locations. These boxes should be placed on poles (stick with steel, it’ll last as long as the box, or longer.) Wood poles will disappoint you in the coming years, I promise. It’s essential to ensure boxes are placed at a height of 10 to 12 feet off the ground. Growers should also make sure the entrance hole is facing away from prevailing winds to keep the interior dry and comfortable for the owls.
Maintaining the boxes is relatively straightforward. Growers should check them periodically (annually, or at least every other year) to ensure the owl pellets from the previous year are cleaned out. Cleaning the boxes once a year, typically before the breeding season occurs in late December to early January, helps encourage owls to return and use the boxes for nesting.
Success Stories and Benefits
Growers report significant benefits from using barn owls for gopher control. For example, a vineyard in California saw a dramatic reduction in gopher damage to their vines after installing several barn owl boxes. The owls quickly took up residence and began hunting the gophers, leading to healthier vines. In another case, an almond orchard experienced fewer young tree losses and reduced irrigation system damage thanks to the presence of barn owls. Other growers report having less gopher mounds in their almond orchards, reducing their need to replace mower cups and blades and saving them money.
Beyond pest control, the use of barn owls also contributes to a farm’s sustainability goals. By reducing the need for chemical poisons and traps, growers can lower their environmental impact and promote a more natural balance within their agricultural systems. This approach aligns with the principles of regenerative farming, which emphasize working with nature to create resilient and productive landscapes.
Barn owls are remarkable birds, playing a vital role in controlling rodent populations and maintaining the health of agricultural ecosystems. By using barn owls for pest control, growers can reduce their reliance on chemical control, protect their crops and help to conserve these beautiful birds for future generations.
Gophers, along with voles and field mice, are notorious for their extensive tunneling activities, which can cause significant damage to crops (photo by Vicky Boyd.)
As growers and consultants seek cost-effective and sustainable ways to manage pests, the use of barn owls offers a promising solution. By leveraging the natural hunting abilities of these birds, growers can reduce gopher populations and mitigate the associated damage to crops and irrigation systems. This approach not only addresses an immediate problem but also supports the broader goals of sustainability and ecological health.
Encouraging the presence of barn owls on farms is a testament to the power of nature in solving agricultural challenges. It highlights the importance of working with, rather than against, natural processes to create productive and sustainable farming systems. As more growers adopt this method, it has the potential to transform pest management practices and contribute to a more resilient and thriving agricultural landscape.
P.S. Install one barn owl box per 10 acres for managing light to medium populations of gophers.
Nick Davis, MBA, is a PCA and CCA as well as owner of The Owl Box Company. He can be contacted at 559-352-8067 for questions on managing gophers easily and inexpensively.
Figure 1. The flow meter is installed in the main pump system of a processing tomato field. With this setup, the flow meter monitors irrigation information for the whole field (photo by Z. Wang.)
Intensified drought in California has limited groundwater supply for crop production. Therefore, vegetable growers need to implement more efficient and crop-oriented irrigation management. Leveraging online decision-support tools can help growers with real-time, effective monitoring of their irrigation and provide updated irrigation recommendations across the crop cycle. CropManage (CM), developed and operated by UCCE, is a weather-based online decision-support tool that provides recommendations for efficient and sustainable irrigation and fertilization applications. CM combines a wide variety of data inputs including past and future weather, evapotranspiration (ET), satellite imagery, soil physical and chemical properties, irrigation system efficiency and other related variables to generate accurate and timely irrigation and fertilization recommendations based on crop-specific models. Growers can compare their actual irrigation amount and timing to the recommendations made by CM and make the proper adjustment to their crops.
Since 2011, CM has been used by growers, farm advisors and research scientists. CM (https://cropmanage.ucanr.edu/) is a credible, free-access, long-term tool for irrigation scheduling and has been adapted for a variety of vegetable crops (carrots, cabbage, broccoli, lettuce, spinach, etc.), berry crops (raspberry and strawberry), tree nut crops (almond, walnut and pistachio) and agronomic crops (alfalfa and corn). Most of the currently adopted vegetables, however, are mainly produced in the Central Coast, so we have been experimenting with Solanaceous and Cucurbits (processing tomato and watermelon) that dominate the Central Valley to examine the feasibility of adapting CM into these warm-season vegetables.
Table 1. Comparisons of watermelon grower’s actual total application of irrigation (inches per acre) and split between water applied via sprinkler and subsurface drip with the recommendations made by CropManage.
What Did We Do?
Since 2021, we have conducted numerous trials in the northern San Joaquin Valley to compare growers’ irrigation scheduling with the recommendations made by CM to determine if CM is potentially adaptable to processing tomato and watermelon irrigation management.
Figure 2. The flow meter is installed in the main blue flat in a watermelon field. With this setup, the flow meter records irrigation information only for the monitored area (photo by Z. Wang.)
Each field trial began with taking pre-plant soil samples and then was followed by setting up the flow meter, moisture sensors and communication devices to access real-time irrigation information remotely. The location where a flow meter is set highly depends on the setup of the field irrigation system. For processing tomato trials, the flow meter is usually connected to the main pump to monitor the whole field irrigation because all irrigation lines and sub-lines are underground, whereas the flow meter is typically connected to a main line in the watermelon trials to monitor the downstream acreage (Figures 1 and 2). The communication devices include a datalogger that saves the information of each irrigation event (duration, flow rate and total volume) and a cellular modem that transfers the data collected by the datalogger to CM (Figure 3).
Figure 3. The configuration and wiring of the communication devices. The flow meter in Figures 1 and 2 was connected to the CR300 datalogger (top) to store flow rate, duration and total volume of each irrigation event. The collected data communicates with the Cell210 cellular modem (bottom) and becomes available simultaneously in CropManage. A 12V battery (right) and a solar panel shown in Figure 2 were used to supply energy to the devices. (photo by Z. Wang.)
As an ET-based irrigation tool, CM provides irrigation recommendations based on the following equations:
Equation 1: Total ETcrop = Avg. ETref × Avg. Kcrop × days since last irrigation
Equation 2: Recommended irrigation amount = Total ETcrop × 100 ÷ (IDU × (1 – leaching requirement)) – total precipitation
In Equation 1, Total ETcrop is the actual evapotranspiration of processing tomato or watermelon in our cases; ETref is the reference ET near the field, which is accessed through the California Irrigation Management Information System (CIMIS), and Kcrop is the crop coefficient for processing tomato or watermelon, which directly relates to the crop canopy development over the crop cycle. By taking the in-field measurement of percent canopy coverage or accessing the coverage data through NASA’s Satellite Irrigation Management Support (SIMS), CM will provide daily crop coefficients (Figure 4).
Figure 4. Left: Watermelon canopy development curve generated by CropManage over the growing season. We collected the user data (green square) weekly in the field using an infrared camera. The SIMS canopy data (dark diamond) were obtained through NASA SIMS System. Right: Seasonal watermelon crop coefficient generated based on the ETref and crop canopy development.
In Equation 2, IDU stands for irrigation distribution uniformity, which is typically between 85% to 95% for subsurface drip irrigation for processing tomato and watermelon production. If using sprinkler or furrow irrigation, the IDU could be less than 75%. Leaching requirement is the fraction of applied water, including rainfall, that drains below the root zone. Growers can set the leaching requirement to zero when subsurface drip irrigation is used to ease the process of calculating irrigation recommendation. Typically, as no precipitation occurs during the growth of most warm-season vegetables in the Central Valley, Equation 2 can be simplified to Equation 3. Figure 5 shows an example of how much irrigation is recommended by CM. Growers can then adjust the actual irrigation amount based on the CM recommendation (Figure 6).
Equation 3: Recommended irrigation amount = Total ETcrop ÷ IDU (expressed as %)
Figure 5. An example showing the process of calculating the recommended irrigation in CropManage.Figure 6. The comparison of CropManage’s recommended irrigation (0.64 inches) vs grower’s applied irrigation amount (0.60 inches). Since we have the flow meter and communication devices connected, the actual water applied is autopopulated from the flow meter to CropManage without the need to download from datalogger or check the flow meter reading in person.
Adaptability in Processing Tomatoes and Watermelons.
For watermelon, the total amount of water applied was dramatically different among years (2021-23). The biggest difference was contributed by the amount of sprinkler irrigation for transplant establishment. Due to drought conditions in 2021 and 2022, 19 and 14.5 inches of sprinkler irrigation, respectively, were made to transplants prior to shifting to the subsurface drip, whereas only 2 inches of sprinkler irrigation was applied in 2023 (Table 1). Because our flow meter only connected to the lines of the drip system, the information of total amount and schedule of sprinkler irrigation was provided by growers. In Table 1, if we only focus on the CM recommendations for subsurface drip system, it is clear the recommended total amounts were close to the grower’s actual applications in all years. For processing tomato, growers took a well adoption of CM irrigation recommendations with differences of less than 4 inches per acre in 2022 and only 0.3 inches per acre in 2023 between the actual total application and CM recommendations (Figure 7).
Table 1. Comparisons of watermelon grower’s actual total application of irrigation (inches per acre) and split between water applied via sprinkler and subsurface drip with the recommendations made by CropManage.Figure 7. Comparisons between the actual cumulative applied irrigation to processing tomatoes and recommendations made by CropManage in 2022 (top) and 2023 (bottom).
FAQs from Users
Attending CM training workshops is another way to get familiar with this decision-support tool. Each year, we host over 10 in-person workshops statewide as well as virtual trainings. Below are the most frequently asked questions from the workshop attendees and grower-collaborators.
What information do we need to enter in CM when setting up the monitored field?
To get more accurate recommendations, we ask users to put in detailed information about the commodity (crop type, acres of the monitored area, coordinates of the field and planting and harvest dates), irrigation settings (water source, nitrogen concentration in the water, irrigation application rate [typically expressed as inches/hour] and distribution uniformity), soil type (autopopulate with entering the field coordinates) and crop settings (previous crop, crop total nitrogen uptake and water stress setting for crops requiring water reduction or cutoff).
If I don’t have the communication devices, can I still use CM to manage my irrigation application?
Yes. As shown in Figure 6, with the flow meter connecting with communication devices, the actual water applied is autopopulated from the flow meter to CM without the need to download from datalogger or check the flow meter reading in person. Without these devices, you can still have your irrigator keep the irrigation duration and enter the hours of irrigation to CM manually. Then, CM will transfer hours of application to inches applied based on the irrigation settings entered earlier.
I don’t have time to measure the crop canopy coverage. Can I only rely on NASA’s measurements?
Yes, but you need to make sure the field is clean from weeds, especially in the furrows (Figure 8). The percent canopy coverage generated by NASA’s satellite imagery system cannot separate weeded areas from the true coverage of cash crop.
Figure 8. Weed infestation in the furrows of the watermelon field due to sprinkler irrigation and possibly ineffective weed control. In this case, watermelon canopy coverage collected by NASA SIMS will be greater than the actual coverage, potentially resulting in inaccurate irrigation recommendations (photo by Z. Wang.)
I have many fields to manage. Can I assign other farm crew for the fields that rely on CM for irrigation?
Yes. In the Ranch Settings, you can assign as many ranch members as you like and give them different levels of access permissions (e.g., view only vs permission to edit settings).
Can I export the field settings and irrigation information?
Yes. If you have full permission, you can export your field settings and cumulative irrigation charts, which can be viewed as an Excel or PDF file.
What are some resources that can help with my use of CM?
CropManage has a knowledge base including tutorial guidance and more FAQs (help.cropmanage.ucanr.edu/tutorials/). Also, keep an eye on the Veg Views Newsletter for future CropManage hands-on trainings (cestanislaus.ucanr.edu/news_102/Veg_Views/).
If I begin using CM in my field, will you help us co-manage the irrigation?
Yes. If you need, I will be working with growers to set up CM and deliver recommendations. We will work together to make sure CM provides timely and accurate irrigation recommendations, which will serve as an important reference for your irrigation decisions.
Figure 1. Dead stems showing symptoms of shepherd’s crook in alfalfa (photo by S. Orloff.)
Roundup Ready technology builds genetic resistanceto glyphosate into crops, providing an excellent tool for weed management. Initial screening in the early 2000s found good crop safety in alfalfa, leading many growers to rely on glyphosate as the only herbicide. Although using the same chemical control season after season is not a good idea because it may accelerate herbicide resistance in weeds, Roundup Ready alfalfa has been successfully used with few to no concerns. However, the combination of glyphosate and cold weather may cause crop injury, especially in regions where frost events typically follow the herbicide application in spring.
It All Started in Siskiyou County
The issue was first observed in 2014 by Steve Orloff, former UCCE farm advisor in Siskiyou County. A Roundup Ready alfalfa field showed injury after glyphosate application followed by freezing temperatures. The main symptoms were plant stunting, chlorosis and “shepherd’s crook,” in which individual alfalfa stems curl over and die (Figure 1). Yield reductions were also observed for the first cutting. Steve noticed the injury could be related to the glyphosate application because a section of the field where an irrigation wheel line prevented the herbicide application looked perfectly normal.
Injury Symptoms Were Like a Known Disease
Interestingly, the injury seen was very similar to symptoms caused by frost and/or bacterial stem blight (BSB) caused by Pseudomona syringae, a waterborne bacteria present everywhere. The bacteria can exacerbate frost damage due to its protein that mimics a crystalline structure and provides a starting point for ice formation, damaging the plant tissue and serving as an entrance port into the leaves and stems. Once into the plant tissue, colonization leads to infection and symptoms about 7 to 10 days after the frost event. Symptoms on stems start as water-soaked lesions that extend down one side. Leaves become water-soaked and often are twisted and deformed. Currently, there are no resistant alfalfa varieties nor effective control methods besides harvesting the crop earlier.
Let the Research Begin
Steve replicated the symptoms in field trials conducted in 2015-17. The field trials showed yield reductions of up to 0.7 tons/acre in the first cutting in Scott Valley. Crop injury was not observed in a similar field trial conducted in 2014, probably because there was no frost event after the glyphosate application. Similar impacts were observed in a trial at the UC Intermountain Research and Extension Center, near Tulelake, Calif.; additional yield reductions were observed with higher glyphosate rates (Table 1).
Table 1. Yields of first and second cutting in 2015 in the Intermountain Region of California. Trial conducted by Steve Orloff.
Broadening the Scope of the Research
Based on this work, a multi-year project started to investigate the effects of glyphosate rate and application timing at 24 sites over five years, measuring the impact on alfalfa crop height and biomass yield. Results were published in the Agronomy Journal in 2023 (Loveland et al. 2023). All locations in this study were in the Intermountain West (California and Utah), and results showed while summer glyphosate application did not injure alfalfa, spring applications reduced crop height at 76% of the sites and biomass at 62% of the sites.
In sites where glyphosate application resulted in crop injury, low (22 oz/acre) and high (44 oz/acre) rates of glyphosate reduced yields by 0.24 tons/acre and 0.47 tons/acre, respectively (Figure 2).
Figure 2. Effects of low and high rates of glyphosate on crop height and yield when compared to untreated check (UTC). Only sites that showed statistical significance were depicted in the graph.
Data also showed the crop height at glyphosate application influenced the degree of injury (Figure 3), with greater yield reductions at 30 to 40 cm (12 to 16 in) than at 5 to 10 cm (2 to 4 in).
Figure 3. Alfalfa yield response (Mg ha -1) to glyphosate applied at six alfalfa heights up to 40 cm (16 in) at four sites in California and Utah in 2019 (Loveland et al. 2023).
Do Alfalfa Growers Need to Panic?
As alarming as the possibility of injury might sound, its occurrence and degree are widely variable, and the crop resumes normal growth and yields after first cutting. Figure 4 illustrates this complexity and variability throughout experimental sites where harvest yield and crop height were assessed. Note the locations represented in the following graph are colder than the San Joaquin Valley and the injury happened after glyphosate applications in spring.
As of 2024, this type of injury has mostly been reported in the Intermountain West due to its high altitude and cooler weather. However, one field I visited in early February 2024 in Firebaugh, Calif. brought my attention back to the issue. The field was planted in fall 2023 and had many of the symptoms previously mentioned: plant stunting, typical shepherd’s crook, chlorosis and dead stems. While all these symptoms could be exclusively due to bacterial blight infections or frost, parts of the field where glyphosate application was accidentally skipped looked better.
Figure 4. The percentage of sites (17) where spring-applied glyphosate reduced alfalfa first cutting yield, height at harvest, both or neither (Loveland et al. 2023).
Considerations and Recommendations
The exact role of glyphosate, temperature, and P. syringae in the injury is unclear. Although most of the sites in this research showed some level of injury followed by glyphosate application in the spring, the degree of the damage was widely variable. Interestingly, injury symptoms worsened with increasing glyphosate rate and crop height up to when alfalfa was 8 inches tall, but the crop somehow seemed less susceptible when glyphosate was applied at 8 to 16 inches tall.
While the initial cases of BSB of alfalfa were reported in 1904 in Colorado, relatively few cases were reported during the second half of the 20th century. However, the disease has become increasingly problematic in past decades, especially in areas where frost events are favorable. Would the re-emerging BSB in alfalfa have something to do with the extensive use of Roundup Ready technology and the overreliance on glyphosate?Future research is needed to answer this question.
Current UC IPM weed management guidelines for Roundup Ready alfalfa recommend rotating herbicides with different modes of action to reduce the development of herbicide-resistant weeds and avoid glyphosate overuse during the colder winter months. Second, spray glyphosate when the alfalfa is short (<2 in) when using the higher rate (44 oz/acre) or 4 inches when spraying at the lower rate (22 oz/acre). Third, use the lowest glyphosate rate possible according to the weeds present and their stage of development; a soil residual herbicide tank mixed with early glyphosate application should provide adequate late-emerged weed control. Finally, pay attention to the weather forecast; applying glyphosate before frost events increases the likelihood of crop injury, especially in old stands.
References
Loveland, L.C., Orloff, S.B., Yost, M.A., Bohle, M., Galdi, G.C., Getts, T., Putnam, D.H., Ransom, C.V., Samac, D. A., Wilson, R., and Creech, J E. (2023). Glyphosate-resistant alfalfa can exhibit injury after glyphosate application in the Intermountain West. Agronomy Journal, 115, 1827-1841. https://doi.org/10.1002/agj2.21352
Crop yields are often lower in organic production systems compared to conventional farming systems (De Ponti et al. 2012). This yield difference is partly attributed to challenges in providing plants with the right nutrients, especially nitrogen (De Ponti et al. 2012; Gaskell and Smith 2007). Organic fertilizers must be broken down by soil organisms before N becomes available to plants in the form of ammonium (NH4+) and nitrate (NO3–), a process referred to as N mineralization (Figure 1). The speed and efficiency of this breakdown depend on the properties of the organic fertilizer (Cassity‐Duffey, Cabrera, Gaskin, et al. 2020; Geisseler et al. 2021). For instance, products with lower C:N ratios and liquid products are known to have a faster N release compared to products with higher C:N ratios and dry products, including pellets and composts (Lashermes et al. 2010; Lazicki et al. 2020). With this knowledge, fertilizer products can be chosen to best meet the crop’s N demand. Despite an increasing understanding of N mineralization rates of organic fertilizer, there is still large uncertainty around predicted release rates. One source of this uncertainty surrounds the impact of soil properties. Organic vegetable growers observe variations in nutrient program performance across fields, highlighting the need to understand how soil properties affect organic fertilizer breakdown rates. Research has shown differences in N mineralization from organic fertilizers between soils, but the reasons for these differences are not well understood (Lazicki et al. 2020; Marzi et al. 2020). Soil texture and pH are thought to impact organic fertilizer breakdown (Cassity‐Duffey, Cabrera, Franklin, et al. 2020; Thangarajan et al. 2015), but a thorough assessment of soil properties’ influence is lacking.
Figure 1. Overview of the nitrogen cycle. Green boxes and arrows represent nitrogen pools and processes within the soil-plant system. Gray boxes and arrows represent nitrogen loss pathways. Orange boxes and arrows represent nitrogen inputs.
Soil Laboratory Experiment
To address knowledge gaps on how soil properties affect N breakdown of organic fertilizers, we determined N mineralization rates of a commonly used 8-5-1 pelletized organic fertilizer in 72 soils with diverse properties (Figure 2). Composite soil samples were gathered from organic vegetable production fields in California’s Santa Maria Valley in fall 2020. This region, located at 34.9530 degrees N, 120.4357 degrees W, is a significant area for vegetable cultivation, boasting a variety of soil types and a Mediterranean coastal climate. Typically, these fields yield two to three crops annually. The valley features several soil series (Table 1), each with its own distinct soil properties.
Figure 2. Schematic overview of the experimental design.
We assessed 25 soil properties (Table 2), including soil texture, soil organic matter, soil organic carbon (SOC), soil organic nitrogen (SON), concentrations of ammonium (NH4+) and nitrate (NO3–) nitrogen, pH levels, electrical conductivity (EC), cation exchange capacity (CEC), exchangeable sodium percentage (ESP), concentrations of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfate (SO4-), mineralizable carbon (min-C), permanganate oxidizable carbon (POXC), carbon and nitrogen in particulate organic matter (POM) and mineral-associated organic matter (MAOM) fractions. All analyses were conducted using standard methods (Miller et al., 2013; Hurisso et al. 2016; Cotrufo et al. 2019). Mineralizable carbon (min-C), also referred to as soil respiration, is an indicator of microbial activity, while permanganate oxidizable carbon (POXC), also referred to as active carbon, can be considered a microbial food source. Both min-C and POXC are commonly used as indicators of soil health (Moebius-Clune et al. 2016; Norris et al. 2020). Meanwhile, POM and MAOM fractions can be interpreted as labile and more stabilized soil organic matter pools, respectively (Cotrufo et al. 2019; Lavallee et al. 2020).
Table 1. Dominant soil series in the Santa Maria Valley vegetable production region, based on the USDA Natural Resources Conservation Service soil survey.
All 72 soil samples were incubated for 28 days at 25 degrees C and 60% water holding capacity, both with and without the addition of organic fertilizer. The organic fertilizer used was a pelleted mix derived from meat and bone meal, poultry manure and feather meal (8-5-1), applied at a rate of 50 mg N per kg soil. This application rate corresponds to approximately 100 kg N per hectare (89 lbs. per acre), assuming a soil density of 2,000,000 kg per hectare in the top 15 cm of soil, consistent with rates reported by growers using split applications. Before application, the fertilizer was ground into a fine powder and thoroughly mixed. We measured NH4+ and NO3– concentrations on days 0, 7 and 28 of the incubation. The percentage of fertilizer N mineralized after 7 and 28 days was calculated as the difference in mineral N (NH4+-N + NO3–-N) over time between samples with and without fertilizer, divided by the amount of fertilizer N applied (Lazicki et al. 2020).
Table 2. Spearman correlation coefficients and p-values for correlations between the percentage of organic fertilizer nitrogen mineralized and various soil properties as predictor variables (n = 72). Significant spearman correlations (p < 0.05) are shown in bold.
Key Findings and Implications
We observed a wide variation in the percentage of N mineralized after 7 or 28 days of incubation (Figure 3). The mineralization rates ranged from -31% to 78% after 7 days and -22% to 87% after 28 days. Negative values indicate N was tied up in the soil after fertilizer application. On average, across all soils, 32% of the fertilizer N was mineralized after 7 days and 27% after 28 days. These results suggest soil characteristics can have a large impact on N mineralization from organic fertilizers.
Our findings are consistent with previous research. For example, a study comparing 22 commercial organic fertilizers found N mineralization ranged from 25% to 93%, with most N being mineralized within the first week. Similarly, in our study, the largest portion of fertilizer N was released within the first 7 days, with more subtle changes between days 7 and 28. Negative rates of N mineralization from organic amendments are found for inputs with high C:N ratios, but other studies typically find net mineralization for commercially available organic fertilizers. It’s important to note the application rate of organic fertilizer in our study was low compared to many other studies, so it is possible the balance between mineralization (release) and immobilization (tie-up) of N may depend on the application rate.
Figure 3. Histograms for the percentage of fertilizer nitrogen mineralized after 7 (blue) and 28 (yellow) days of incubation across 72 soil samples.
We found several significant correlations between soil properties and the percentage of fertilizer N released after seven days of incubation. For example, N mineralization after seven days was positively correlated with clay content, SOM, SOC, SON, CEC, pH, nitrate nitrogen, Olsen phosphorus, soil potassium, calcium, magnesium and microbial biomass nitrogen content. This suggests that fostering soil organic matter or soil carbon and general soil fertility may benefit the efficiency at which organic fertilizers are mineralized, especially during the first week following fertilizer application. In contrast to our expectation, the soil health indicators min-C and POXC and the organic matter fractions POM and MAOM performed poorly in predicting organic fertilizer mineralization in our study. Significant negative correlations were found with sand content, electrical conductivity and exchangeable sodium percentage. Negative effects of salinity and sodicity on organic fertilizer mineralization imply a compounding challenge for growing crops in saline or sodic soils under organic management.
Our study demonstrates organic fertilizer mineralization is influenced by soil properties. Maintaining pH, EC and ESP within the optimum range is important to ensure sufficient N mineralization from organic fertilizer. Fertilizer mineralization rates were greater at higher soil organic matter and soil nutrient concentrations, highlighting the importance of building these for efficient fertilizer use in organic crop production. Future research should focus on management practices that are most effective and cost-efficient for building soil organic matter and fertility to support reduced organic fertilizer input costs in the medium and long term. Our findings suggest in organic production systems, nutrient management should consider not only plant nutrient demand but also the nutrient demand for building and maintaining soil health and fertility.
The authors are grateful for support from Betteravia Farms for soil sample collection and analysis. Songyi Kim provided support through the Korea National Institute for International Education, Ministry of Education. Finally, this project could not have been completed without the technical support of Craig Stubler for laboratory analyses.
References
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Figure 1. Silverleaf nightshade is widespread in California (a); blue dots indicate the distribution of the weed. Silverleaf nightshade affects young pistachio orchards in the southern San Joaquin Valley (b) (map courtesy CALFLORA 2024.)
Silverleaf nightshade, Solanum elaeagnifolium, is a perennial weed native to South America, Mexico and the southwestern and southern U.S. It is widespread in California where it affects diverse agricultural and non-agricultural systems, including orchards, rangeland, pasture, roadsides and disturbed areas. Because it readily adapts to high temperatures, low rainfall and saline and drought conditions, silverleaf nightshade is a problem in orchard systems. It is widely distributed in California and is currently affecting both young and mature orchards (Figures 1 and 2). Silverleaf nightshade is currently affecting young pistachio orchards in western Fresno and Kings Counties. In Tulare County, it is found in pistachio orchards that were planted in unmanaged fallow land or in fields near roadsides where it is commonly found. In mature orchards, missing trees create gaps in the canopy, thus allowing light penetration to the orchard floor and enabling establishment of resident populations of silverleaf nightshade (Figure 2a). In orchard systems, it competes with developing trees for resources, while the toxic glycoalkaloid compounds in the leaves and berries pose an additional threat to livestock and other animals if consumed.
Figure 2. Silverleaf nightshade colonizes open areas in orchards where missing trees allow sufficient light to reach the orchard floor, facilitating growth of the weed (a). In spring, distinct violet and yellow flowers (b) on the current season’s growth are a diagnostic feature, as well as the berries remaining on the prior year’s growth (c).
Identification Silverleaf nightshade is an herbaceous, perennial weed belonging to the Solanaceae family along with other weeds, including black nightshade (Solanum nigrum), hairy nightshade (Solanum physalifolium) and horsenettle (Solanum carolinense). The mature plant is generally 1 to 3 ft high and can be readily identified by the small yellow to brown berries (~0.5 inch in diameter) and silver-gray foliage that often contains prickles (Figure 2c). The flowers are violet with distinct yellow centers (Figure 2b).
Life Cycle Silverleaf nightshade is difficult to control because of its perennial life cycle in California. It emerges in early spring to late summer, with new plants growing from both seed and rhizomes. It flowers from summer to early fall, generating around 200 small fruits on each plant. Each fruit may contain 24 to 150 seeds. The seeds may be dispersed by birds that have consumed the fruit or by the movement of soil. The plant is also disseminated by movement of soil containing rhizome fragments. The mature plant dies back with the first frost, but the rhizomes survive underground.
Impacts The weed competes with young orchard trees for resources, such as water, light and nutrients. If left unmanaged, silverleaf nightshade can also interfere with irrigation operations and potentially reduce vigor of young trees. Since silverleaf nightshade can adapt to alkaline and saline soils, it has the potential to outcompete many of the summer annual weeds and become the dominant weed in a population.
Management Silverleaf nightshade is difficult to control in orchards. Tillage is not recommended because the movement of rhizome fragments may result in spread of the weed across orchards. Mowing can be an effective strategy to prevent weeds from setting seed. Flail mowers are often used in orchards and vineyards to mow weeds in between tree rows. After mowing, however, new silverleaf nightshade shoots may sprout from underground rhizomes, regenerating the weed. Despite the efficacy of mowing, most commercial mowers will miss weeds in the tree row. Hand weeding can be used to remove some of the weeds around the trees, but precautions need to be taken to protect the skin because mature plants are covered with reddish prickles. Weeding tools, such as shovels and hula hoes, are effective but can damage surface drip hoses if the user is not careful.
Herbicides can be an effective weed management method to control silverleaf nightshade in different tree and vine crops. There are six post-emergent herbicides and one preemergent herbicide registered for use in trees and vines in California (Table 1). Preemergent herbicides are normally applied during the dormant season and most only control weeds before they germinate. Preemergent herbicides will not control silverleaf nightshade that emerges from rhizomes in the summer. Post-emergent herbicides can be used to control silverleaf nightshade that emerges in the summer and early fall before harvest. In the summer months, a combination of mowing and the use of post-emergent herbicides can kill the aboveground tissues of silverleaf nightshade and deplete the belowground propagules in soil. Post-emergent herbicides need adjuvants, such as nonionic surfactants and crop and seed oils, to increase their efficacy.
Table 1. Herbicides registered for use in California tree and vine crops (https://wric.ucdavis.edu/).
Specific to pistachio, there are 12 preemergent and 13 post-emergent herbicides with different modes of action that are registered. Pendimethalin, rimsulfuron, mesotrione, flumioxazin, isoxaben and flazasulfuron are herbicides that have great control over black and hairy nightshade. Isoxaben can suppress silverleaf nightshade but can only be used in pistachios that have been established for at least three years. Glyphosate, glufosinate, pyraflufen-ethyl, paraquat and carfentrazone are post-emergent herbicides with different modes of action that can be used to control different weeds and can be used up to two weeks before harvest. 2, 4-D is another post-emergent herbicide that is registered for use in pistachios but needs to be applied to trees that have been established for at least one year and has a preharvest interval of 60 days. Studies have shown glyphosate and 2, 4-D have excellent control of silverleaf nightshade. Glyphosate is a systemic herbicide that can potentially kill the root and rhizome system of silverleaf nightshade when applied at the correct timing and rate. Furthermore, always consult herbicide labels on information regarding the required adjuvants, preharvest intervals, application rates and maximum applications per season.
Because silverleaf nightshade is a problem in mature olive orchards adjacent to the foothills in Tulare County, UCCE Weed Management Advisor Jorge Angeles (Tulare and Kings counties) recently initiated a study evaluating post-emergence herbicides, alone and in combination, for management of the weed. A suite of 10 treatments was applied in late Spring 2024, and preliminary data on treatment efficacy will be available by late July. Angeles is also interested in establishing a trial in late winter to evaluate efficacy of pre-emergence herbicides for management of silverleaf nightshade in table olives.
Silverleaf nightshade is difficult to control because of its adaptability to diverse agricultural systems, its tolerance to many herbicides and its perennial nature. A combination of cultural practices, such as mowing between tree rows, and implementation of an herbicide program with products containing multiple modes of action should be used to develop an effective management strategy for silverleaf nightshade. Additionally, developing and maintaining field records before planting is a great way to determine the history of a field, and weed surveys in the winter and spring can help determine what weed species are present in a field. Last, to prevent introduction of silverleaf nightshade into orchards, it is important to sanitize tractor equipment and manage the weeds that grow on the field edges or near irrigation canals.
Aerial photos with (left) and without (right) cover crops (photos courtesy Andrew Gal, UC Davis.)
Growers in the west are facing more and more pressure to account for their water use. On May 13, Sustainable Conservation (SusCon) released a report entitled Cover Cropping in the SGMA Era, summarizing two years of convenings held by SusCon with over 100 scientists, crop advisers and other agricultural professionals and stakeholders. The report distills research and working knowledge of the aspects of cover cropping impacts upon soil water budgets in the context of the Sustainable Groundwater Management Act (SGMA) and associated Groundwater Sustainability Agencies (GSAs).Specifically, the report provides three areas of information derived from hours of convenings and interviews with GSA representatives:
1. A research summary of cover crop impacts to the water cycle, focused on California, Mediterranean and semi-arid climates
2. An investigation about impacts SGMA and GSA management may have on the use of cover crops
3. Recommendations for statewide water planners regarding the use of cover crops as a Climate-Smart Practice
Cover Crops Use and Management in California Cover crops are a non-cash crop grown for multiple benefits. Cover cropping is generally recognized as an option for growers to fill a void and armor the soil between cropping seasons. The USDA Natural Resources Conservation Service (NRCS) incentivizes growers to grow cover crops across the nation, and the CDFA Healthy Soils Program incentivizes growers to grow cover crops in California.
In addition to soil armoring, cover crops are recognized to provide a wide array of ecological services, that include improved water infiltration, water quality protection, erosion control, weed suppression, pollinator support and nutrient cycling to name a few. Cover cropping as a conservation practice is also one of USDA’s climate-smart agricultural practices because the practice also sequesters carbon, which improves soil health by feeding microbial populations and improves climate resiliency by the simple fact it holds soil together with its roots. In California’s Mediterranean climate, where most of the annual precipitation occurs between the months of November and March, cover crops are generally planted in the fall and rely on rainfall to grow. They are terminated in spring using various methods and at different times, depending on the crop, field conditions, operation schedules and grower’s objectives for using the cover crop in the first place.
Prior to World War II, cover cropping was a common practice, especially the use of leguminous cover crops to provide nitrogen for crop production. In the 1950s and beyond, an increased prevalence of commercial fertilizers coincided with a decrease in use of cover crops. Over the past 30 to 40 years, cover cropping interest grew, paralleling society’s growing interest in agricultural sustainability, organic farming, the environment and soil health.
Prior to the widespread interest in soil health in California, it was not unheard of for crop advisors to discourage cover cropping due to concerns for water competition with the cash crop. Following SGMA, a similar and more serious controversy evolved regarding the potential impact of cover crops upon groundwater supply.
Hydrological processes that may be influenced by cover crops. This illustration depicts the major flows of water occurring on a parcel that cover cropping has the potential to impact (source: Cover Cropping in the SGMA Era.)
Sustainable Groundwater Management Act and Cover Crop Water Use Amid one of the most severe droughts in Californian history (2012-14), SGMA was instituted by the state to build a framework of GSAs to protect aquifers from overdraft using local jurisdiction. The drought accelerated groundwater use, causing groundwater in parts of the state to drop 50 to 100 feet below previous historical lows.
Several years ago, the agricultural community heard stories about growers avoiding cover cropping due to the fear of being penalized by their local GSA for allowing cover crops to grow on their farms. Further investigation by SusCon and other stakeholders showed cover crops may be unintentionally discouraged by GSAs because of the water budget accounting methods used that. at times, incentivized the maintenance of bare ground. Methods used for water accounting, such as satellite imagery, were based upon the assumption that cover crops have an evapotranspiration (ET) value that negatively impacts groundwater recharge. Research on cover crop water use increased in 2016, when a group of UC Davis researchers began to investigate the topic more closely to try to answer some unknowns about the potential of cover crops to impact the soil water balance and aquifer recharge.
It is an undeniable truth that winter cover crops use water for establishment and growth until termination in spring. How much water they use is what has shown difficult to answer precisely, and this value changes based on many factors, such as soil texture, climate, time of year, ground cover, the cover crop being grown and timing of cover crop termination. Recent studies as outlined in the report show winter cover cropping can use between 1 and 2 inches for establishment, which in some cases falls within a “margin of error” for annual irrigation rates for cropping systems (Smither-Kopperl pers. comm. 2024, DeVincentis 2023).
In some locations in California, growers do not plant cover crops because the climate and water supply will support multiple cash crops in a single year. With climate change, these options may become more limited, and growers and agronomists will have to seek out other opportunities for maintaining soil health between growing cycles. I recently heard about innovators exploring the use of “precision cover cropping,” whereby plantings are in narrow bands to either coincide with a cash crop’s rooting area or to address specific soil health and soil quality issues, like soil crusting and compaction.
Cover crop adoption rates in California and other states have hovered around 0% to 5% for years. In the SusCon report, cover crops include prescribed planting of cover crops (native and non-native) and volunteer groundcover (weeds). Many conservation entities encourage prescribed planting of cover crops to achieve and maximize multiple benefits and ecological services. Nevertheless, whether they’re intentionally planted or not, living ground cover in the fields during off seasons protects the soil.
Ironically, at times, the discussion of whether cover crops compete for water with the following crop seemed to be isolated from the discussion of the many ecological services they provide, namely increased water infiltration and decreased runoff, the two most pronounced hydrological services cover crops can provide.
Table 1. Confidence in potential cover crop impacts to water budgets. Based on available, contextually relevant information, there is higher confidence that cover crops increase infiltration, decrease runoff and erosion and that water use is affected by termination timing. Factors such as the impacts on evapotranspiration (and the drivers of those impacts) are less understood (source: Cover Cropping in the SGMA Era.)
Summary of Findings The SusCon report is an in-depth account of the current state of knowledge for soil water impacts of cover crops in Mediterranean climate regimes. Key findings outlined in the report were:
• Cover cropping improves the soil ecology and water cycling and provides other benefits.
• Impact of cover crops on water budgets is highly variable and depends on an assortment of factors, not limited to climate, soils and management.
• Cover cropping has shown to have a negligible impact on ET compared to bare ground in perennial and annual systems in Mediterranean climates.
• Wintertime, rain-fed cover cropping does not significantly increase water losses compared to bare ground in the winter months.
• California-based research literature showed the dominant water-balance benefits of cover cropping are increased water infiltration into the soil and the reduction of runoff, frequently ≥40% for both pathways.
From its research, Suscon developed five core recommendations to support SGMA implementation for sustainable water use in California:
1. Create a coordinated research approach to improve understanding of the impact of cover crops on net water balances.
2. Identify and address knowledge gaps that would allow GSAs to permit integration of cover cropping within their jurisdictions.
3. Support GSAs with up-to-date scientific information and guidance related to satellite ET, flow meter data and consumptive groundwater.
4. Improve data acquisition processes for key ET data and high-resolution data essential to GSA management, which would improve the quantity and quality of the data.
5. Provide funding to improve technical support for GSA that support research and guidance documents related to key ET data inputs.
This report gives me great confidence that water managers, growers, crop advisors, scientists and stakeholders can find ways to effectively use cover crops where it makes sense to do so. We can design the cover crop management strategies to accommodate multiple environmental benefits and match strategies to location and geography when we find cover crops appropriate to use. These designed benefits can and will include water conservation.
Resources
California Dept. of Water Resources, (February 2015) California’s Most Significant Droughts: Comparing Historical and Recent Conditions https://cawaterlibrary.net/wp-content/uploads/2017/05/CalSignficantDroughts_v10_int.pdf
DeVincentis, A., Solis, S. S., Rice, S., Zaccaria, D., Snyder, R., Maskey, M., Gomes, A., Gaudin, A., & Mitchell, J. (2022). Impacts of winter cover cropping on soil moisture and evapotranspiration in California’s specialty crop fields may be minimal during winter months. California Agriculture, 76(1), 37–45.
Ingels, C., Horn, M. V., Bugg, R., & Miller, P. R. (1994). Selecting the right cover crop gives multiple benefits. California Agriculture, 48(5), 43–48USDA ERS. (2023). State Fact Sheets: California [dataset]. https://data.ers.usda.gov/reports.aspx?StateFIPS=06&StateName=California&ID=17854
Kratt (February 2024) “Cover Crop Use in California and Measurable Outcomes” Progressive Crop Consultant
Lloyd, Margaret (May 2023) The Costs and Benefits of Growing a Cover Crop in an Annual Rotation in the Lower Sacramento Valley Progressive Crop Consultant
Mitchell et. al; (2023) Water Related Impacts of Cover Cropping. YouTube Video.https://www.youtube.com/watch?v=mTNLx6LzEt0
Sustainable Conservation (May 2024) Report:Cover Cropping in the SGMA Era.https://suscon.org/blog/2024/05/ccrop-report-release/
USDA ERS, Wallender et al. (February 2021) Economic Information Bulletin Number 222 Cover Crop Trends, Programs, and Practices in the United States https://www.ers.usda.gov/webdocs/publications/100551/eib-222.pdf
Wyant, Karl (March 2023) “The Agronomy of Water” Progressive Crop Consultant
Dr. Alireza Pourreza collecting grape leaf hyperspectral reflectance using a backpack spectrometer equipped with a leaf clipper and looking at the measurement in real time (all photos courtesy A. Pourreza.)
Accurate nitrogen monitoring and appropriate nitrogen management are crucial in California due to the state’s unique environmental challenges and agricultural practices. N is essential for crop growth, but excessive use can lead to serious environmental issues, including groundwater contamination and the emission of nitrous oxide, a potent greenhouse gas. The Central Valley, a major agricultural area, has seen significant N inputs from both synthetic fertilizers and manure, leading to widespread nitrate pollution in groundwater, a critical issue since many communities rely on groundwater for drinking. To address these challenges, California has enacted regulations that require more precise N applications aligned with crop needs. This initiative aims to reduce the amount of excess N that can leach into groundwater or run off into surface waters. The regulations, such as those detailed by the Central Valley Regional Water Quality Control Board, include requirements for growers to submit Nitrogen Management Plans that report both the N applied and the N removed by harvested crops. This approach helps calculate N use efficiency and identify areas where improvements are necessary.
Overfertilization poses several risks to both plants and the environment. In plants, excess N can cause stress and overproduction of leaves, making them more susceptible to diseases. It can also reduce yield and decrease quality, including organoleptic quality, and reduce the content of mineral nutrients and secondary metabolites. Additionally, high nitrate content in leaves can be harmful. Environmentally, excess N that remains unused in the soil can leach below the root zone or be lost through run-off, leading to nitrate accumulation in natural water bodies. This can cause algal blooms, eutrophication and acidification of freshwater lakes and coastal areas. Nitrate-contaminated drinking water requires expensive treatments, and nitrous oxide emissions from denitrification and manure decomposition processes on agricultural sites contribute to global warming. These emissions also negatively impact terrestrial and aquatic ecosystems.
Conversely, N deficiency negatively affects photosynthetic assimilation and reduces crop yield both in terms of quantity and quality. It restricts the development and growth of roots, suppresses lateral root initiation, increases the carbon-to-nitrogen ratio within the plant, reduces photosynthesis and results in early leaf senescence. Therefore, monitoring N levels accurately and managing them precisely is essential for maintaining the health of both crops and the environment, particularly in California, where agricultural practices must align with stringent environmental regulations.
Leaf Spectrometry Leaf spectrometry is a powerful technique used to measure the spectral reflectance of plant leaves across a wide range of wavelengths. This process involves collecting hyperspectral data, which refers to the reflected light from leaves. Each leaf has a unique spectral signature that changes based on its biochemical and biophysical properties, such as leaf pigments, protein and carbon-based contents, and moisture content. By analyzing these spectral signatures, researchers can infer various properties of the leaves, which provides valuable insights into the plant’s health and nutritional status.
Several tools are commonly used to measure leaf spectral reflectance. One of the primary instruments is a spectrophotometer, which can capture detailed reflectance data across different wavelengths. Portable leaf spectrometers, used in many studies, offer a more convenient and flexible option for field measurements. These tools are designed to be lightweight and easy to use, making it possible to collect high-quality spectral data directly from the plants in their natural environment. By utilizing these advanced tools, researchers and growers can obtain precise information about leaf properties, enabling more accurate monitoring and management of plant health and nutrient levels.
The process to create a mechanistic remote sensing model. In order from left to right, this involves spectral analytics at the leaf level, a nitrogen prediction model, scaling up the leaf-level knowledge to generate a canopy-level radiative transfer model that simulates the spectral characteristics of vine and retrieves plant traits, and a nitrogen status map that illustrates the spatial variability of plant nitrogen contents in a field.
Practical Application and Implementation Imaging spectroscopy and leaf spectrometry have vast potential applications in agriculture, particularly for N management in vineyards. These technologies allow growers to monitor vine health and nutrient status accurately, providing essential data that can lead to more precise and efficient decision-making and farming practices. Detailed spectral data reveals changes in leaf biochemical and biophysical properties, some of which are indicative of the vine’s N content.
Spectral modeling approaches for N retrieval have evolved significantly. Traditional methods often relied on simple correlations between basic vegetation indices or specific wavelengths and N levels. While these methods were quick, they could be overly simplistic. Modern approaches utilize advanced techniques, such as chemometrics and machine learning algorithms, to analyze spectral data. Chemometrics involves using statistical methods to extract meaningful information from complex spectral data, providing more accurate and comprehensive insights into N levels. Machine learning algorithms have become increasingly popular. These models can process large datasets and learn intricate patterns, offering high accuracy and robustness in N estimation.
Alternatively, physically based models, or radiative transfer models (RTMs), simulate the mechanism of light interaction with plant tissues to estimate biochemical/biophysical properties. These models are highly accurate and consistent and can be applied across various conditions, though they require detailed input data and calibration. Combining RTM with machine learning techniques, creating hybrid models, can further enhance their accuracy and applicability. Hybrid models use detailed simulations from RTMs to train machine learning algorithms, resulting in systems that can adapt to different environmental conditions and crop types. Implementing these advanced spectral sensing techniques in vineyards involves several practical steps. First, growers need to collect hyperspectral data from their crops using either portable ground-based spectrometers or aerial spectral cameras. This data is then analyzed using one of the above modeling approaches, whether it’s chemometrics, machine learning or a hybrid method. Depending on the modeling approach, the results can potentially provide detailed insights into the N status of the vines, allowing for precise and targeted fertilizer applications.
Case Study We conducted a study to compare various analytical methods for N retrieval in grapevine leaves using hyperspectral data. Our primary goal was to determine the most effective approach for accurately and consistently estimating leaf N levels, considering both purely data-driven empirical methods and more sophisticated mechanistic models like PROSPECT and hybrid modeling techniques.
N in plants is primarily found in proteins, which are critical for various physiological processes. Proteins in the leaves contribute significantly to the N content, making the measurement of protein levels a consistent indicator of N status. Traditional methods often rely on the relationship between chlorophyll content and N, but this approach can be misleading due to the small proportion of N in chlorophyll and the dynamic nature of N allocation within the plant.
Empirical methods, such as those using simple vegetation indices like the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Red Edge (NDRE), have been widely used for estimating N content. However, these indices often fall short of providing accurate and consistent results for vine N content. NDVI and NDRE are sensitive to changes in chlorophyll content but do not capture the full complexity of N dynamics within the plant. Their reliance on a few spectral bands can lead to inaccuracies, particularly under varying environmental conditions and growth stages.
The PROSPECT model simulates how light interacts with leaf tissues, providing a more detailed and physically based approach to estimating N content. By incorporating specific absorption coefficients for proteins, PROSPECT can more accurately represent the biochemical processes within the leaves. This model showed robustness and transferability across different conditions but requires full band (400 to 2500 nm) and well-calibrated spectral data.
Hybrid modeling combines the strengths of both artificial intelligence and physically based approaches. By using detailed simulations from PROSPECT to train machine learning algorithms, hybrid models can achieve higher accuracy and adaptability. These models leverage the comprehensive understanding of light interactions provided by PROSPECT and the flexibility and learning capacity of machine learning techniques.
The advantages and disadvantages of four different spectral modeling approaches:
• Vegetation Indices (NDVI, NDRE, etc.): quick and easy to use but often inaccurate and inconsistent for detailed N estimation.
• Empirical Data-Driven Methods (Machine Learning): high accuracy with large datasets but can be prone to overfitting and may require extensive training data.
• Physically Based Models (PROSPECT): highly accurate and robust but complex and data-intensive.
• Hybrid Models: combines the best of both worlds, offering high accuracy and adaptability with a solid physical basis.
Our study demonstrated while traditional vegetation indices are useful for general assessments, they are insufficient for precise N management in vineyards. Advanced methods like RTM and hybrid models provide a more reliable and detailed understanding of N dynamics, paving the way for more effective and sustainable vineyard management practices. By leveraging these advanced analytical techniques, vineyard managers can optimize N use, improve crop health and reduce environmental impacts. If adopted by growers, this data-driven, decision-making vineyard management approach will support compliance with stringent environmental regulations, promote sustainability, drive the future of precision agriculture and optimize crop production.
Resources
The peer-reviewed paper: sciencedirect.com/science/article/pii/S0034425723005187#f0005
In the world of agricultural sales, particularly within the rich and varied landscapes of California, understanding and overcoming objections is paramount. As experienced sales professionals and crop consultants, your role transcends mere transactional exchanges; it’s about building trust, understanding needs and offering solutions that genuinely benefit our farming partners. Here, I’ll share my insights on navigating these waters effectively.
1. Listen Intently: Before you can overcome an objection, you need to fully understand it. Listen to the grower’s concerns without interrupting. This not only shows respect but also gives you the necessary information to address their specific issues.
2. Empathize and Validate: Growers want to know you understand their situation. Acknowledge their concerns and empathize with their challenges. A simple “I understand why that could be a concern” goes a long way.
3. Educate and Inform: Use your expertise to educate the grower about the benefits and features of the product. Present data, case studies and testimonials that align with their concerns. Remember, knowledge is power, but it must be relevant to their specific circumstances.
4. Tailor Solutions: Customize your solutions to address the grower’s unique needs and conditions. Show how your product or recommendation directly resolves their issues or improves their operations.
5. Highlight ROI: Growers are business owners who care about the bottom line. Discuss the return on investment and how the product can increase efficiency, yield or quality in the long term.
6. Address Risks Directly: Don’t shy away from discussing potential risks. Be honest about them and discuss how these risks can be managed or mitigated. This honesty builds trust and credibility.
7. Utilize Third-Party Validation: Bring in success stories, testimonials or endorsements from other growers and industry experts. Peer approval can be a powerful motivator.
8. Create a Sense of Urgency: Without being pushy, explain any time-sensitive benefits of acting now, such as limited availability, current pricing or seasonal advantages.
9. Offer Trial or Pilot Programs: If possible, offer a trial period or a pilot program. This lowers the barrier to entry by reducing perceived risk.
10. Be Patient but Persistent: Change can be daunting. Allow the grower time to think but follow up regularly. Persistence shows commitment and can often be the key to eventual agreement.
In my years of experience, these strategies have been instrumental in navigating objections and building fruitful relationships with California growers and other agricultural businesses. It’s about more than just selling a product; it’s about fostering partnerships and contributing to the success of their agricultural endeavors.
Remember, every objection is an opportunity in disguise, an opportunity to educate, to build rapport and to find mutual ground. With the right approach, patience and understanding, objections can be transformed into gateways for growth and collaboration. As sales professionals and crop consultants, your goal should always be to serve as trusted advisors, guiding farming partners toward decisions that enrich their lands and their livelihoods.
