If you are using irrigation to water, it’s important to know its quality and understand the pounds-per-acre concepts of potentially problematic minerals being applied (photos courtesy Cameron Newell and Jesse Kay-Cruz, Xerces Society.)
All throughout the wine grape world and across the U.S., wine grapes are grown on a variety of soil types and climates. AVA regions have started to be defined in places like Arizona where vineyards are thriving on challenging aridisol soils that can be difficult for Vinifera to thrive in comparison to other longer-established regions. Understanding the parts of the soil report and irrigation water quality have become paramount in understanding how to attain the highest level of viable production and maintain the healthiest soils.
It’s not uncommon for the focus of soil reports to center on one item in that report or look at results in a way that can detract from how to get to a fertility program that will serve the budget, crop and soil health most efficiently.
There are five items to look at in order on a soil report to obtain balance and increased overall soil health. It is important when obtaining soil reports to ask the lab you are working with to compute the Cation Exchange Capacity (CEC) and Base Saturation levels. I see a great deal of results from growers who come to my firm looking for recommendations that do not have CEC or base saturation levels defined. It’s impossible to make precise recommendations without these.
Irrigation Water Quality
Dryland-farmed vineyards don’t have this concern or need worry about the problems associated with irrigation water quality. However, if you are using irrigation to water, it’s important to know its quality and understand the pounds-per-acre concepts of potentially problematic minerals being applied. Normally, water is seen as clear and refreshing; not knowing what is contained in water and what normal usage brings is no different than shoveling on bicarbonates, salts, sulfates, boron and chloride directly on the crop. This is an important place where we can find the sources of issues constraining production and limiting soil health and balance.
Cover cropping and getting that green biomass back into the soil is one way to help build a help build soil organic matter levels.
Cation Balance
Cation balance is the most important component of a soil report. Many worry most about pH, but the pH will balance itself out when the specific issues are addressed in the soil. Depending on CEC, one should see Ca levels at 60% to 70%, Mg at 10% to 20%, K at 2% to 5%, Na at 1% to 4% and H at 5% to 10%. It’s important to fall back and understand Mulders Chart, realizing the antagonistic and synergistic relationship between minerals in soils. Identifying imbalances in mineral nutrition can lead to soling mysteries behind cropping outcomes. Cation balance is not overly difficult in most cases, granted it may be a situation where there is a two-to-four-year strategy to attain the corrections needed.
Phosphate Levels
In the southwest, there has been a feeling developed that it is okay to accept lower P levels and production will not be hindered. In other regions, P levels are normally very adequate. These lower levels of 10 to 25 parts per million (ppm) are widely accepted. It has been observed that controlled vigor and balance are attained when soil P levels are found in the 50- to 100-ppm range. Further observations show that as that number approached 100 ppm, there is improved plant health, controlled vigor and improved juice numbers. Delivering P can be challenging, but there are good conventional and organic ways to apply. It most likely serves best to look toward a dry program and have a three-to-five-year goal of building soil P to a level that is acceptable.
Organic Matter
In the desert southwest, I often don’t see organic matter (OM) levels above 1%. Ideally, 4% to 10% is acceptable. In certain regions, this may be a difficult level to attain. Further, in some regions, there can be an issue finding a compost source to help build soil OM levels. Leaning on dry leonardite sources and/or liquid humic additions can be ways to help build soil OM levels. Further, cover cropping and getting that green biomass back into the soil is another means to help build a healthy soil. Increasing OM levels increases CEC, buffers pH and helps nutrient uptake in the soil profile.
Sulfur, Boron, Chlorine and EC
Grapes are not incredibly tolerant of salts and subsequently can be severely hindered by excess amounts. Keeping sulfur, boron and chloride levels to a minimum is very important. Looking at CEC and Ca base saturation levels, one can find the levels acceptable. Keeping boron 1/1000 of Ca or not exceeding 4 ppm is critical to avoid toxicity, with sulfur being 1/3 to 1/2. P is an acceptable range. Cl should be one to two times Na by weight.
Soil health does in fact hinge on mineral balance in the soil. Balancing rations between soil minerals is key to allowing for optimal soil health in vineyards. These are simple ways to break down a soil report and what is maybe influencing it. It is important to spend the time, money and all-around effort to address mineral balance and the items discussed here prior to seeking certain products targeted for soil health.
Figure 1. Affected vines are easily distinguishable by their premature senescent leaves during the fall, while healthy vines are still green (all photos courtesy A. Eskalen.)
Grapevine canker diseases are commonly associated with fungal pathogens of the Botryosphaeriaceae, Diatrypaceae and Diaporthaceae families. These pathogens have been found and described in many cultivars worldwide. Symptoms include internal wood necrosis, stunted or poor shoot development after the budbreak and dieback of cordons or the entire vine. Cankered tissues may also exhibit dark fruiting bodies (pycnidia and perithecia) on the surface, which are responsible for releasing the spores that will lead to further infections in the vineyard.
A different wood canker disease was first detected in the San Joaquin Valley in 1989, affecting excessively vigorous young ‘Red Globe’ grapevines (Michailides et al. 2002). Since then, the disease has been observed on different cultivars, including Chardonnay, Grenache and Crimson Seedless. The pathogen was morphologically identified Aspergillus niger, a member of the group of black aspergilli, or Aspergillus section Nigri, and the disease was named as Aspergillus Vine Canker. From 2003 to 2010, Aspergillus vine canker was detected and monitored in Italy, affecting several table grape cultivars on different growing regions (Vitale et al. 2008, Vitale et al. 2012). In this case, three species of black aspergilli were associated (A. awamori, A. carbonarius and A. tubingensis). Recently, through a collaboration with UCCE farm advisors, we identified Aspergillus vine canker on Grenache and Malbec cultivars in Fresno and Sonoma counties, respectively. Symptomatic vines tested negative for viral infections.
Figure 2. Black sporulation is evident at the surface and underneath the bark of affected tissues, which is key to distinguish Aspergillus from other trunk pathogens that usually form fruiting bodies that are embedded in the wood.
Symptoms
Affected vines are easily distinguishable by their premature senescent leaves during the fall, while healthy vines are still green (Figure 1). A single vine can harbor multiple cankers located on different parts of the vine, including the trunk, cordon and spurs. Black sporulation is evident at the surface and underneath the bark of affected tissues, which is key to distinguish Aspergillus from other trunk pathogens that usually form fruiting bodies that are embedded in the wood (Figure 2). Internally, a brown discoloration is evident in the xylem near the margin of the cankers (Figure 3a), whereas the areas under the sporulation show necrosis and black discoloration near the bark (Figure 3b). In severe cases, the canker can girdle most of the vascular area.
Figure 3a and 3b. Internally, a brown discoloration is evident in the xylem near the margin of the cankers (left), whereas the areas under the sporulation show necrosis and black discoloration near the bark (right).
Current Investigations
Our lab has been focusing on the specific identification of the causal agent of Aspergillus vine canker in California using molecular tools, particularly by constructing phylogenetic trees using DNA sequences of the calmodulin gene. Preliminary data suggest that our isolates correspond to Aspergillus tubingensis, a closely related species to the previously identified A. niger. Since morphological features cannot separate both fungal species, two hypotheses can be indicated, either the old and new isolates correspond to the same species (A. tubingensis) or they are different (A. niger and A. tubingensis). Coincidently, black aspergilli are known to cause sour rot on grape berries. In California, two species (A. niger and A. carbonarius) have been described as causal agents of sour rot disease on table grapes (Rooney-Latham et al. 2008). Therefore, we are currently studying the phylogenetic relationships between Aspergillus isolates from wood cankers and sour rot berries to understand accurately the etiology and epidemiology of both diseases.
Management Strategies
Aspergillus vine canker has not been thoroughly studied given its sporadic occurrence in California. Therefore, the only management strategies include cultural practices, such as obtaining clean plant materials, identifying diseased vines in the fall and removing affected parts by cutting them back below the canker during dormant season or removing the entire vine.
References Michailides, TJ., W. Peacock, P. Christensen, DP. Morgan, D. Felts. 2002. Plant Dis. 86:75. https://doi.org/10.1094/PDIS.2002.86.1.75A Rooney-Latham, S., C. N. Janousek, A. Eskalen, W. D. Gubler. 2008. Plant Dis. 92(4):651. https://doi.org/10.1094/PDIS-92-4-0651A Vitale, A., Castello, I., Polizzi, G. 2008. Plant Dis. 92:1471. https://doi.org/10.1094/PDIS-92-10-1471B Vitale, A., G. Cirvilleri, A. Panebianco, F. Epifani, G. Perreno, G. Polizzi. 2012. Eur J Plant Pathol 132:483–487 https://doi.org/10.1007/s10658-011-9906-z
Western grape leafhopper, variegated leafhopper and Virginia Creeper leafhopper all suck out liquid from grape leaf cells, causing loss of photosynthesis, reduced vigor and even leaf drop when in high densities. Affected leaves will have white stippling (photo by Jack Kelly Clark, courtesy UC Statewide IPM Program.)
Erythroneura leafhoppers can be a significant insect pest in organic vineyards as well as regions of California where biological control is inadequate.
The Western grape leafhopper (Erythroneura elegantula) is a pest in the San Joaquin, Sacramento, Central Coast and North Coast regions. The variegated leafhopper (Erythroneura variabilis) is in southern California, San Joaquin Valley, southern Sacramento Valley and occasionally found in Napa County. Virginia Creeper leafhopper (Erythroneura ziczac) is mostly found in the Sacramento Valley and Sierra Foothills, but over the past 10 years has started to infest North Coast vineyards as well, especially Lake and Mendocino counties.
The Western grape leafhopper, variegated leafhopper and Virginia Creeper leafhopper all suck out liquid from grape leaf cells, causing loss of photosynthesis, reduced vigor and even leaf drop when in high densities. Affected leaves will have white stippling. If high populations of leafhoppers are present, fruit quality and yield can be affected. Adult leafhoppers can also be a nuisance to workers at harvest.
Leafhoppers overwinter as adults in leaf litter and weedy vegetation in and around vineyards. They emerge in the spring to feed on new shoots and lay eggs under the surface of the leaves. Adults and nymphs feed on the leaves.
Houston Wilson, Cooperative Extension Specialist (Dept. of Entomology, UC Riverside) at the Kearney Agricultural Research and Extension Center, said the Western grape leafhopper is usually controlled by the egg parasitoids Anagrus erythroneurae and Anagrus daanei, which are common in many California vineyards. Parasitoids attack the egg stage, and if their population builds in a vineyard, they can keep leafhoppers in check. These parasitoids overwinter outside of the vineyard, primarily on coyotebrush and blackberry, and it has been shown that the closer these plants are to the vineyard, the earlier parasitoid activity will begin in the vineyard.
Biological control of the variegated leafhopper and Virginia Creeper leafhopper is more challenging since the populations of parasitoids that attack these species tend to vary from region to region. Additionally, eggs of the variegated leafhopper are deposited deeper into the leaf tissue, which makes it more difficult for parasitoids to access and attack. Wilson said the key parasitoids for these species include Anagrus daanei and Anagrus tretiakovae. While Anagrus daanei can be found in the Central Valley, Sierra Foothills and Coastal regions, Anagrus tretiakovae is much more limited.
Wilson received funding from DPR in 2015 to research the different strains of leafhopper parasitoids in California and determine why Virginia Creeper leafhopper eggs in the North Coast wine grape regions were not being parasitized. Surprisingly, Anagrus daanei in the North Coast appear to not attack Virginia creeper leafhopper, even though they will readily do so in other regions of the state. Between 2015-17, Wilson worked to introduce a strain of Anagrus daanei into the North Coast that would attack Virginia Creeper leafhopper, but it did not establish. Wilson is hoping to reinitiate this area of his research program in the next year.
Many grape growers rely on the use of systemic neonicotinoids for control of leafhoppers since these products can be quite effective. As such, recent leafhopper outbreaks have been primarily limited to organic vineyards. That said, there is potential for both resistance and/or regulation of neonicotinoid use in California, at which point effective biological control will be critical to all growers.
Adult Asian citrus psyllid feeding on new flush. Citrus industry efforts are aimed at controlling this pest which can transmit citrus greening disease, or Huanglongbing (photos courtesy Citrus Research Board.)
Citrus growers throughout California can apply to be part of the Citrus Research Board’s (CRB) California focused Citrus Research and Field Trials (CA-CRaFT) program. This project is aimed at development and demonstration of additional mitigation measures for Asian citrus psyllid (ACP) control across all citrus growing regions of California.
Project Manager Ariana Gehrig said the project will have an advisory committee to review and select grower applications to implement innovative psyllid management strategies for enhanced grove-level control of ACP. Growers who apply for this project will receive reimbursement for costs associated with their participation.
In the first year of the project, growers will be invited to apply and implement additional control methods in commercial groves. Data collected will be used to demonstrate changes in psyllid populations resulting from mitigation measures. Data collection and implementation of control strategies are expected to continue into the second year. Findings will be shared with citrus growers to promote effective treatments and share best practices.
Gehrig said there will be two types of ACP mitigation efforts: preventative and threshold. Preventative measures could involve use of living wind breaks or fence-type barriers to protect citrus orchards from ACP infestations. Use of trap crops grown in or adjacent to orchards is another type of mitigation measure. The threshold category might include border treatments, ACP repellents or ant control. Biological control agents include the release of the ACP parasitoid Tamarixia radiata or generalist predators.
Gehrig said although participation is open to all citrus growers, the advisory committee will make selections based on growing region, variety of citrus, age of groves and mitigations selected. Growers may apply for projects in multiple blocks. The preferred size is 5 to 40 acres.
Grower applications will be available soon for the CA-CRaFT project. The CRB was awarded $3,438,059 from the Huanglongbing Multi Agency Coordination Group to support the CA-CRaFT project. CRB will administer the program for two years with intent to renew.
“We are excited to develop the first CRaFT project for citrus in California as this project will bring new energy to the fight against HLB and benefit growers across the state while investing in vital research,” said CRB President Marcy Martin.
The California Strawberry Commission’s technology production team created a retrofittable cutting apparatus for mulch hole punching. The larger hole made by the new tool allows more water and sunlight to reach the strawberry plants (photo courtesy CSC.)
While strawberries are one of California’s high-dollar crops, the labor required to not only harvest, but to perform other cultural tasks comes at a considerable cost. UC figures show that labor costs can be $25,000 to $39,000 per acre. In addition to hand harvest, there is runner cutting, pest monitoring and treatment, and the simple but laborious job of cutting holes in the plastic mulch at planting.
Automation has not yet come for harvest, but technological advances in other areas are promising. Dr. Mojtaba Ahmadi, senior production automation engineer with California Strawberry Commission, said that since 2020, the CSC has started to stimulate third-party companies for development of automated runner cutters and to investigate some of the technical aspects of this. Runner cutting is the second largest labor cost after harvest, Ahmadi said.
The engineering team has developed a deep learning framework to detect and identify runners by using RGB image data as well as exploring different methods to improve data collection. Ahmadi said the CSC has also collaborated with the Massachusetts-based Strio AI, a robotics startup, to develop an automated runner cutter.
This effort was successful in building a robotic platform that was able to maneuver in strawberry fields and, with use of a robotic arm, fusion RGB and depth data, successfully performed runner cutting.
Obstacles to the use of robotic runner cutting, such as cost, complexity of the electronics and maintenance difficulties ,have yet to be overcome, Ahmadi said.
Lygus monitoring and treatment is another focus of CSC technology efforts. Ahmadi said work is continuing on machine vision technologies in combination with vacuum technology. The aim is to determine how effective the vacuuming operation is in removal of lygus.
“We know speed matters, both tractor speed and vacuum air speed as well as height of the vacuum from canopy level,” Ahmadi said. Monitoring these can help the tractor driver know if the settings are accomplishing the job.
Plastic mulch hole cutters are typically driven through fields just prior to planting. Ahmadi said that the hole punchers leave narrow openings in the plastic that may prevent adequate water and sunlight from reaching plants. The production team developed a tool that can be attached to the current hole punchers to widen the holes without deforming the planting hole in the soil. Grower testing has proved this modification can be applied in commercial strawberry production.
Tulelake alfalfa growing on residual moisture in late June 2021. Soils there have high water holding capacity to sustain crops during the early part of the growing season. Alfalfa’s deep rooting systems can tap into soil moisture (photo by D. Putnam.)
It is a mistake to let an alfalfa field ‘limp along’ on inadequate irrigation throughout the growing season, letting yields and quality suffer. The better strategy for hay production, according to UCCE Specialist Dan Putnam, is to fill the soil profile early and get as much yield as possible and then allow the stand to go dormant.
“It is a resilient crop. It can come back within the fall when it receives some moisture,” Putnam said.
Filling the soil profile early will give growers the two to three cuttings that are usually higher in yields and quality than those later in the season.
Alfalfa growers throughout the state can develop strategies to keep good alfalfa stands productive in drought conditions. Putnam said the first step is to decide which fields or parts of fields will benefit the most from what irrigation water is available. Those should have priority. Alfalfa stands nearing the end of their productive life, those on soils that do not hold moisture well or spotty stands are best left to go dormant to direct water to alfalfa stands that will benefit the most.
Ending irrigation in mid- to late summer for alfalfa fields will not end their productive life. The stands will turn brown and go dormant, but generally won’t be lost. Depending on the soil type, Putnam said, most of the time alfalfa will recover with fall rains or irrigation. Putnam pointed out that 60% to 65% of annual alfalfa yields in most parts of California are achieved by mid-July.
Putnam wrote in a UC publication that alfalfa has a key role in California’s water-uncertain future due to its high flexibility during times of insufficient and excess water. Alfalfa’s deep roots tap into residual soil moisture. Multiple harvests can give partial economic yields when irrigation ceases. Alfalfa roots survive summer dry-downs and will come back when re-watered. Alfalfa fields can be flooded in winter to recharge aquifers. The crop also has high salinity tolerance.
Alfalfa has proved to be highly flexible and resilient in surviving droughts while sustaining productivity, even when as little as half the water requirement is applied, Putnam said. The resilience of alfalfa was demonstrated during the 2021 drought in the Tulelake area where a full yield of two cuttings of alfalfa was observed with zero irrigations. Only six inches of rainfall occurred before March. Alfalfa roots were deeper than eight feet. The soils there have excellent water holding capacity, Putnam said, but the production showed the resiliency of alfalfa with limited water supply.
Further discussion of strategies for drought conditions can be seen at a blog on drought at https://ucanr.edu/blogs/Alfalfa/.
The California Central Valley supplies 80% of almonds globally, so ensuring the health of these trees is essential. However, young trees are highly susceptible to damage from phytoparasitic nematodes, and chemical fumigation is often necessary to ensure protection. Rory Crowley, a conventional almond and walnut grower, partnered with the Simmons lab at UC Davis to find a natural, sustainable yet effective alternative to chemical fumigation.
“Any thoughtful producer in the Central Valley, whether organic or conventional, understands that we simply cannot continue farming the way we are, especially as it relates to traditional chemical fumigation,” Crowley said. “Indeed, as Dr. Amélie Gaudin has recently said, ‘An entire consortium of scientists has argued for years that our current ways of farming simply cannot go on.’ So, we decided to go with something new.”
Researchers in the Simmons lab, working in collaboration with the UC Davis Western Center for Agricultural Safety, specialize in biosolarization, a soil amendment technology that combines biological, thermal and natural chemical control to reduce plant diseases without fumigation. Biosolarization also provides a closed-loop recycling strategy for agricultural waste streams like almond hulls and shells. These byproducts provide valuable soil amendments due to their high organic carbon content and are co-located with almond orchards.
Figure 1. Biosolarization schematic.
Implementation and Principle
With current technology, three components are necessary for biosolarization:
Soil Amendments: The addition of organic matter (OM) increases the population and activity of beneficial saprophytes (detritus-eaters), which can suppress pathogenic organisms through competition or through the production of biopesticidal chemical compounds. Agricultural and food processing residues act as low-cost soil amendments for biosolarization.
Transparent plastic tarp: Covering moist soil with a clear tarp promotes soil heating through the greenhouse effect. During hot summer months, covered soil can reach surface temperatures over 120 degrees F, temperatures which are lethal to many soilborne pathogens and weed seeds. Elevated temperatures can also leave pathogens more susceptible to biopesticides.
Drip line Irrigation: Irrigation using temporary surface drip lines beneath the plastic tarps fills soil pores, reduces oxygen and hinders gas exchange. When the carbon-rich soil environment becomes anaerobic, fermentative bacteria (Bacilli and Clostridia) can rapidly convert carbohydrates from amendments into toxic organic acids and volatiles.
These three components act synergistically and can provide positive feedback loops. For instance, high microbial activity stimulated by amendments can consume the limited soil oxygen and produce heat as a byproduct. Similarly, the application of amendments and irrigation can change thermal properties of soil and increase solar heating. Because of these combined factors, effective biosolarization treatment durations can be as short as 10 days or less.
Figure 2. Map of field site.
Pre-Plant Orchard Demonstration
Rory’s 8.5-acre almond block in Chico was used as the demonstration site for pre-plant orchard biosolarization in June 2017, and trees were planted the following January. A hull-rich waste stream and a hull and shell mixed waste stream from a local nut processer were selected as soil amendments.
Residues were applied to plots at a rate of 15 tons per acre and tilled to a depth of seven inches. Soil was then covered with transparent tarp and irrigated to field capacity. For comparison, additional plots were treated with solarization (tarped without amendment) or left untreated. Soil remained tarped for six weeks.
Figure 3. Abundance of the phytoparasitic nematode Pratylenchus vulnus.
Nematode Control
Parasitic nematodes (lesion and ring) were detected in soils before biosolarization took place. After 10 days of tarping, nematodes in the first 12 inches of soil were below detection levels in biosolarized soils and nearly undetectable in solarized soils.
When tarps were removed after six weeks of treatment, rows underwent deep tillage in preparation for planting. This effectively reduced nematode levels in the upper 12 inches of soil across all plots regardless of treatment. However, two months after the tillage, reemergence was observed (albeit at low levels) for all but the hull-rich biosolarized plots. As a result, the timing of deep tillage should be considered as a possible complementary control measure. To avoid bringing viable phytoparasitic nematodes from deeper soil layers into the treated root zone, deep tillage should ideally be performed ahead of solarization or biosolarization.
Soil Ecology
Even before tarp application, the incorporation of almond hulls and shells enriched soils with saprophytic taxa (e.g., Bacilli and Streptomyces), demonstrating how amendments can ‘shift’ soil communities to promote organic matter degradation.
After six weeks of tarping, microbes associated with low-oxygen and high-heat environments became significantly enriched in biosolarized and solarized soils (e.g., Clostridia). These microbes can ferment the sugars in almond hulls to produce acetic acid and other biopesticidal chemical compounds.
These enriched taxa remained elevated in treated soils even two months post-treatment. This may indicate prolonged degradation of fibrous organic residues, which has been linked to long-term pathogen suppression due to continued biopesticide production. Some of the microbes identified in biosolarized soils have also been associated with improved soil and plant health outcomes.
Figure 4. Relative abundance of key fermentative anaerobe classes (Bacilli and Clostridia) associated with biopesticidal chemical production.
Orchard Monitoring
Almond tree saplings (Bennett-Hickman, Monterey and Nonpareil varieties with K86 rootstocks) were planted in orchard rows six months post-biosolarization treatment (Jan. 2018), and bi-annual sampling timepoints were used to track soil and crop health through spring 2022. Tree trunk diameters were measured periodically to track growth rate, and soil was periodically sampled to track parasitic nematode re-infestation and soil nutrients levels (Calicum(C), Nitrogen(N), Potassium(K) ).
Almond Tree Growth
During the first year, trees planted in previously-biosolarized rows seemed to grow slower than trees planted in untreated soils. This trend continued until the beginning of the third year, when growth rate appeared to uniquely accelerate in some treated rows. During the fourth year, no differences in growth rate were found between the control and biosolarized trees, indicating successful adaptation of the trees to the treated soil. In one instance, Nonpareil tree diameters were significantly higher in the shell-rich amended rows.
“To be sure, this was a complex project, but the purpose was to prove concept,” Crowley said. “We did that and more. 1After looking at the data, any balanced grower would say that those first two years gave us all a bit of pause. Trunk diameter on the treated row trees were smaller than the controls, yet not once did I think we were going in the wrong direction. I continued to trust Chris and his team, and I trusted the science. I continued to trust my eyes and nose when I smelled the treated soil over against the control dirt. Trunk diameters have now caught up, and in my opinion, will outpace the controls.”
The slowed growth rate of biosolarized trees during the first and second year followed by accelerated growth during the third year suggests that trees may take at least two years to adjust to disturbances caused by degrading residues, but this did not appear to impact long-term growth rates compared to control trees. This also shows the importance of a post-treatment remediation period before crops are planted, though lab studies found soils may recover faster when amendment particle sizes are reduced or applied at lower levels (about 4.5 tons per acre).
Figure 5. Timeline of orchard monitoring.
Nematode Reinfestation
Three years after initial treatment, nematode levels remained low in solarized and biosolarized treated rows, but lesion nematode re-infestation was observed in the untreated rows. Root knot nematodes also became more prevalent in the control soils after three years. Since fumigation has been show to control major phytoparasitic nematodes for approximately two years, solarization and biosolarization appear to at least match the efficacy of conventional pesticides.
Soil Nutrients
Over the first three years of growth, biosolarized soils experienced elevated levels of K, N and C as well as organic matter (OM), a metric associated with improved water-holding capacity, nutrient retention and root biomass. After 3.5 years of tree growth, N, C and OM raw values became elevated in control rows, possibly due to increased nutrient turnover and tree uptake in biosolarized soils.
Figure 6. Colorized NDVI.
Canopy Health
To compare tree health between treatments and tree varieties, multispectral imaging was performed two years after planting and took place each year when the canopy was at peak vegetation. Multispectral imaging captures reflected wavelengths from the orchard to gather data relevant to crop health. For example, healthy vegetation with high chlorophyll levels reflects higher levels of green and near-infrared light than other wavelengths, so rows with more vegetation (and more chlorophyll) would have higher values for green-related metrics than rows with little or poorer vegetation.
Preliminary data have been promising. Certain biosolarized treatments had higher ‘green’ metrics (improved canopy reflectance and color properties) than control trees, indicating greater vegetation levels. However, this benefit was dependent on both soil amendment type and almond tree variety.
Yield and Ripening
Although we do not have yield and ripening data, we do have promising anecdotal evidence from Rory, who managed the orchard last fall during our second harvest. “I got a call from my shaker operator at Nonpareil harvest: ‘Rory, we’ve got a whole row of green nuts.’ I sped over there in my truck. Lo and behold, it was a biosolarization row(s),” he said. “I looked at the control next to it and realized those nuts were ready, dry and shaking off the tree well. When I looked at the biosolarization rows, the nuts were bigger and the quality, by all appearances, was that much better. The nuts were still maturing on the tree, and the overall health of the tree was markedly better. We will prove this out this harvest when we measure crop yield and quality against the controls.”
Conclusions and Recommendations
Both biosolarization and solarization are effective methods for the inactivation of lesion and ring nematodes in the short term, but biosolarization may have longer-term suppression. Effects at deep soil levels (greater than 12”) have not been fully investigated.
Soils treated with biosolarization have higher nitrogen, carbon, potassium and organic matter levels than nonamended soils during the first two years of growth. With fertilizer prices rising steeply, enrichment of plant nutrients in biosolarized soils may be an increasingly important driver for adoption for biosolarization over fumigation or solarization.
Trees may take two years to adjust to disturbances caused by biosolarization.
Growers should conduct trials on test plots before scaling up.
“This powerful alternative to chemical fumigation needs wide adoption, and Chris and his team deserve a huge kudos,” Crowley said. “Onward and upward to the wide adoption and full commercialization of biosolarization with almond hull and shell, and not just in almonds, but in all crops up and down the Central Valley.”
Research to translate biosolarization to almond production has been supported by grants from the National Institute of Occupational Safety and Health (grant #5U54OH007550) and the Almond Board of California (grants #17-SIMMONSC-COC-02 and Q18-BIO-18SimmonsC–0). The authors deeply appreciate the collaboration and support of George Nicolaus to establish the field trial on a Nicolaus Nut Company farm.
References Hodson, A. K., Milkereit, J., John, G. C., Doll, D. A., & Duncan, R. A. (2019). The effect of fumigation on nematode communities in California almond orchards, Nematology, 21(9), 899-912. Shea, E., Wang, Z., Allison, B., Simmons, C.W., 2021. Alleviating phytotoxicity of soils biosolarized with almond processing residues. Environmental Technology & Innovation. 23, 101662. Shea, E, Fernandez-Bayo, J.D., Hondson, A., et al, 2022. The Effects of Preplant Orchard Biosolarization with Almond Residue Amendments on Soil Nematode and Microbial Communities. Applied Soil Ecology. 172, 104343.
Paper cartons that come with the bare root or potted trees from the nursery are the most frequently used tree protectors (photo by C. Parsons.)
Protecting newly planted almond trees from herbicide damage, sunburn or vertebrate pests can help ensure a healthy, productive tree at maturity. There are products that nurseries provide to protect new trees and others that growers choose to purchase for specific uses. Which product to use and how long it should be left in place are important considerations.
Paper cartons that come with the bare root or potted trees from the nursery are the most frequently used tree protectors. Coated with a waxy type material or plastic film, the paper cartons primarily serve as a barrier to herbicides sprayed down tree rows.
Luke Milliron, UCCE orchard advisor in Butte, Glenn and Tehama counties, said there is concern that the paper cartons could disintegrate before the new trees are hardened off and resistant to herbicide injury. On the other hand, leaving paper cartons on the tree too long can also pose risks. In UCCE’s Sacramento Valley Orchard Source, Milliron noted that the paper part of the carton can disintegrate over time, but the coating can hold moisture on the tree trunk. Long-term moisture on the trunk can present the possibility of a Phytophthora infection. Milliron stressed that any trunk protector that keeps the tree trunk wet for a prolonged period is a risk for disease. Even if the carton does not disintegrate, leaf litter can accumulate inside the carton and hold moisture against the trunk or crown of the tree.
Milliron noted that white paint on the tree trunk alone does not protect young almond trunks from herbicide damage. The carton provides the protection from herbicide damage.
The recommendation from former UCCE Advisor David Doll, The Almond Doctor, is to keep cartons on through the summer of the second year for protection for the late spring burn down. That leaves an opportunity to remove them before debris and tree growth makes it difficult.
Cliff Beumel with Agromillora Nursery said other products that provide protection are also available. Taller versions of the carton protectors at 18 inches use the wax type coating but are not as wide as the conventional cartons. Grow tubes, a plastic product, are used with smaller trees. These can provide longer protection from herbicide or other injury and are less likely to trap moisture against the trunk. They come at a higher cost but can be re-used.
Another variation is plastic protection that is white on the outside and black on the inside. Beumel said their cost may be lower, but labor is required to place them on the trees. They do not stay consistently wet and pose less problems for disease infections. One of their main benefits is these protectors block the sun and prevent suckering.
New mating disruption products for California red scale control allow for variable release of the pheromone when it will be most effective in disrupting males (photo courtesy Semios.)
Mating disruption is another tool that may help citrus growers with an integrated approach to control California red scale (CRS) populations in their orchards, potentially enabling them to skip one spray application for this pest.
Heavy infestation of CRS on citrus fruit can cause quality downgrades at the packinghouse, lowering value to the grower. CRS on twigs, leaves and branches can cause defoliation, dieback and, at high numbers, tree death.
Female CRS remain under their covers throughout their life, according to the UC Integrated Pest Management guidelines. When mature, female CRS produce 100 to 150 crawlers which emerge from under the female cover and move or are moved by wind, birds or picking crews. They settle on suitable parts of citrus trees and start feeding. Adult male CRS are small insects that emerge from their scale covers to mate with females. The number of male flights and CRS generations per year varies depending on the location and weather, but four flights per year is average.
Mating disruption for CRS control is not new. It involves use of synthetic pheromones to interfere with the mating process. First used with passive release, the new products allow for variable release of the pheromone when it will be most effective in disrupting males.
Abigail Welch, Semios PCA and entomologist, said that the most common method of predicting the phenology of CRS is by monitoring male trap captures and degree days, the timeline between peaks in life stages.
CRS peak crawler emergence can be expected at 550 DDF after each peak male flight. However, it is common that detection of crawlers during regular field scouting does not appear to line up with the spring biofix model (at 550, 1650, 2750, 3850 DDF after first flight biofix). Detection of male CRS in traps during the third flight may also be affected by biotic or abiotic factors. Later in the season, it is possible that the male flights will overlap. The aerosol dispensers have the ability to match the pheromone release at the right time, improving CRS control.
Welch noted that mating disruption with the aerosol variable rate dispenser as part of an integrated approach to CRS control will be more of a challenge when infestation rates are high but is still a viable option. Just expect to continue with a rigorous CRS management strategy until populations decrease. It is best to use this tool when CRS populations are low to moderate.
Studies show the aerosol dispensers are suitable for one can per season, placed at one per acre from mid-February to late October. The dispensers are placed on conduit poles between trees down the row.
Fall-planted safflower produces large amounts of forage dry matter per acre while requiring very little irrigation water (photo by C. Parsons.)
Continued studies suggest that safflower grown as a winter forage for dairy cows in the San Joaquin Valley has benefits in water savings and recovery of nutrients.
Stephen Kaffka, director of the California Biomass Collaborative and UCCE specialist in the Department of Plant Sciences at UC Davis, said safflower has value as a silage when harvested in the vegetative stage in early spring following November planting. Studies at dairies were completed to determine if the crop has potential as a low-input, high-biomass cattle feed.
While there are some challenges with harvesting and ensiling this crop, it produces large amounts of forage dry matter per acre while requiring very little irrigation water.
Winter planted safflower allows for high water use efficiency and, as it is a very deep-rooted crop, recovers nutrients and water left behind by shallow-rooted crops. An initial study at the UC Davis campus funded by the California Dairy Research Foundation and co-sponsors Nestles and Hilmar Cheese found that safflower used less than 1.5 acre-feet of water (af) from all sources to produce nearly six tons of dry matter biomass per acre by harvest at the end of April. Two studies completed on dairy farms in the southern San Joaquin Valley in 2021 with early April-harvested safflower measured less than one af of irrigation water and similar levels of forage dry matter yield.
Soil water depletion to six feet in the soil profile was documented by researchers in the dairy studies. Most nitrate uptake occurred in the upper portion of the soil profile where roots are denser. Most comparable crops are limited to four to six feet in the soil profile.
Kaffka and UC Davis Dairy Nutritionist Peter Robinson reported that safflower silage was comparable in feed quality to cereal silages made from triticale and wheat, which are typically planted and harvested during the same time period. Safflower silage stores well and was stable over a six-month storage and feedout period, and it did not accumulate nitrate to excess or result in harmful silage gas production under study conditions.
Due to the high moisture content of fall-planted safflower, harvest and drying of the crop posed challenges. Due to harvest in early spring, drying was slow, and forage must be left in wide windrows to achieve sufficiently low moisture for effective silage fermentation. Robinson and Kaffka said limited levels of irrigation, different row spacings, seeding densities and planting dates are included in a current study.
