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.
Pocket gopher tunnels have lateral branches used for feeding or pushing excavated soil to the surface. Fan-shaped soil mounds over tunnel openings are signs of a pocket gopher infestation (photo by C. Parsons.)
Early detection of pocket gopher mounds in a vineyard can help with control decisions and prevent damage to grapevine roots.
These 6- to 8-inch rodents live underground and are rarely seen. They spend most of their time in a tunnel system 6 to 12 inches below the soil surface. The tunnels have lateral branches used for feeding or pushing excavated soil to the surface. These fan-shaped soil mounds over tunnel openings are signs of a pocket gopher infestation.
The UC Integrated Pest Management guidelines for pocket gophers in vineyards note that the tunnel openings are almost always closed with soil plugs unless active excavation is occurring. Gophers can be active throughout the year in vineyards and other irrigated crops. Populations are more likely to be present where there is extensive weed growth, including nutsedge. Cover crops, particularly perennial clovers and legumes, are also favored by pocket gophers. If food is available and no biological or other controls are implanted, populations can increase to 30 to 40 gophers per acre.
Gopher control can be problematic in vineyards adjacent to empty, weedy fields or crops where gophers are not controlled.
Trapping and baiting are listed as the most effective control methods. UCCE Kern County Farm Advisor Julie Finzel said when she receives calls about pocket gophers, she first asks growers what control has been tried and information on the infestation.
Recognition of pocket gopher mounds should be followed by some control methods. Mounding activity is highest through late winter, and the most common controls, trapping and baiting, are easier when vineyard soils are moist. Darker mounds indicate new activity. Nearby vines should be checked for girdling of roots or crowns at or below soil.
Biological and cultural controls include predators who may not keep numbers low enough, tilling which can disrupt tunnel systems and flood irrigation where possible.
According to UCCE Specialist Roger Baldwin, gopher populations don’t cycle like voles do. Over large geographical areas, their numbers are steady across years, although within a specific area, numbers can certainly increase or decrease given local conditions.
The UC Guidelines advise an integrated approach to gopher control. Baiting can be done with multiple dose anticoagulants, strychnine or zinc phosphide, which may require a permit from the county.
Baiting requires finding the main tunnel to place the bait. Start by finding the plug of the gopher mound and probe from 4 to 12 inches behind the plug. A tunnel is found when a drop in the probe is felt.
Trapping also requires some labor and skill for success. The Macabee Gopher Trap or the Gophinator are recommended. Traps need to be fastened in place and their location marked so they can be found.
Baiting with poison is another technique. Special probes that release bait are available. Strychnine and zinc oxide are legal in California for ag use, and they kill with one feeding. Anticoagulants may take multiple feedings. Poisons can have secondary effects. Tractor-drawn devices can create artificial burrows and deposit bait as they do, but soil conditions are critical for effectiveness.
Root-knot nematodes lower carrot quality due to forking and root galling and can significantly lower marketable yields (photo courtesy A. Ploeg.)
Root knot nematodes are the most significant soil pest in California fresh carrot production.
In the 2022 Carrot Research Symposium, UC Riverside researcher Antoon Ploeg reported on 2021 trials of new non-fumigant nematicide products to prevent root knot nematode injury in carrots. The trials were conducted with UC Riverside researcher Ole Becker.
According to Becker’s report to the California Fresh Carrot Advisory Board, root-knot nematodes are widespread in central and southern California carrot production areas and are particularly damaging in lighter soil types. Becker noted that presentations at the carrot symposium narrowly focus on the previous year’s research with funding from the board. He said the trials do not capture the overall project that typically runs for several years.
Root-knot nematodes lower carrot quality due to forking and root galling and can significantly lower marketable yields. This plant parasite also affects other vegetable crops, including tomatoes and peppers, but does not have as large of an impact on marketable yield as in carrots.
The non-fumigant nematicides, Velum, Salibro and two unnamed products T1 and C, were tested. These nematicides were applied pre-seeding at different rates and with and without soil penetrant products. There is a short re-entry time, and no tarping is required after applications. There is no systemic activity or phytotoxicity when applied at recommended rates.
Traditional management for root knot nematode has consisted of the soil fumigants Telone II and metam sodium. Due to buffer zone requirements when using those products, portions of fields must be excluded from treatment. Restrictions on use to reduce emissions can also prevent applications.
The first trial at the South Coast Research Center in Irvine had 10 treatments with an untreated control. The products were sprinkled over the top of the bed and incorporated into the soil three days prior to hand seeding.
Ploeg said that nematode levels were overall fairly low. Some treatments appear to reduce nematodes at harvest, but no significant effects were found.
There were only minor differences in percentage of marketable carrots, results that did not agree with the previous year’s results. This was surprising, Ploeg said, because a previous trial showed that Salibro had a dramatic effect on percentage of marketable yields.
In a second trial, Salibro was both sprinkled and drenched at the regular rate and double rate and compared to the untreated control the double rate sprinkled did show an increase in marketable yield.
Ploeg said the 2022 trials would include some new biological products.
Palmer amaranth is an aggressive weed species that is resistant to glyphosate. In a mature vineyard, it can interfere with harvest and cultural practices (photo by Dr. Katherine Waselkov, Fresno State.)
Weed control in California vineyards requires these ‘little hammers’: mechanical, cultural, physical, biological and chemical.
Continuous use of the same practice will select for weed species that become adapted to that practice. Multiple control tactics will prevent adaptation.
Fresno State University Professor of Weed Science Anil Shrestha, speaking at the 2021 virtual Lodi Grape Day, said resistance challenges in control of vineyard weed species may impact vine health, crop quality and cause economic loss for growers. Young vineyards are most susceptible to competition from weeds.
Integrated weed management is not a new concept, Shrestha said, but as effective herbicides were developed, fewer other tools were used. As weed resistance increased, the integrated approach is again being emphasized.
The International Survey of Herbicide Resistant Weeds (www.weedscience.org) showed that 263 weed species have developed resistance to herbicides. Only three modes of action in herbicides have no reported resistance, Shrestha said, and there are no new chemistries coming in the near future.
In addition to rotating modes of action in herbicide applications, there are steps to take in preemergent and post-emergent weed control that can maximize efficiency. For preemergent products, Shrestha advised removing debris from vineyard floors, using enough water to activate herbicide and to avoid frequent wetting and soil disturbance. Post-emergent weed control is best achieved with timing, meaning applications at early growth stages, using enough water volume and choosing effective nozzles for delivery.
Mechanical weed control in vineyards can be effective, but using the same tool over time can cause a shift in weed species. Shrestha’s example was use of a cultivator or French plow over time that cleaned up horseweed and fleabane in a vineyard, but nutsedge and grasses become an issue.
Palmer amaranth is an example of a more recent weed species to invade California vineyards. It is resistant to glyphosate even at eight times the label rate, Shrestha said. Mexican sprangletop and telegraph weed may also invade vineyards.
Shrestha said it is critical to maintain a weed-free environment around young vines for at least the first two years after planting. Studies showed that aboveground biomass could be reduced by 85% due to weed pressure. Cane length, leaf numbers and root biomass can also be impacted by weed growth.
Established vineyards may tolerate more weed pressure; however, vineyard weeds may also serve as disease or insect pest hosts. Loss depends on age of the vines, life cycle stage of the vines, weed species and density and duration of competition.
Fusarium crown and root rot infections in tomato plants cause a slow decline over many weeks late season. A laboratory diagnosis for this disease is important. No cultivars are resistant (photo by B. Aegerter.)
Powdery mildew is one of the fungal diseases affecting yield and quality in California processing tomato production.
Brenna Aegerter, UCCE farm advisor in San Joaquin County, explained in a UC Ag Experts Talk webinar that tomato powdery mildew (TPM) is caused by three different pathogens depending on environmental conditions. Leveillula taurica is the primary TPM pathogen in arid or semi-arid conditions. Early symptoms of this disease are yellow and light-green lesions on leaves that grow in size. The initial symptoms progress into necrotic and dead leaves with sporulation on either side of the leaf. Spores spread in the air.
Tomato powdery mildew infections increasing one month prior to harvest may affect soluble solids without affecting yield. Early season high disease pressure may significantly reduce yields.
Preventative applications are needed, Aegerter said. Two-week treatment intervals may be too long when disease pressure is high. To optimize chemical control, it is recommended that treatment begin early and to consider other target pests and diseases when choosing a control product. Good coverage that penetrates the canopy is needed. For resistance management, product rotations, tank mixes or formulated mixtures, include sulfur dust in the program when feasible.
Aegerter said younger plants are more susceptible to TPM and late-season fields experience heavier disease pressure. Proximity to other diseased fields and variety tolerance are also considerations. Plant stress may worsen mildew problems.
Field trials in Solano and Fresno growing areas showed that weekly sulfur dust significantly reduced TPM, but the degree varied by location.
Other fungal diseases affecting tomato production are Verticillium wilt, Fusarium, Southern blight and black mold.
Verticillium wilt is an early season disease that is widespread in California production tomato areas. Dry leaves in June and vascular discoloration can be signs of this disease as temperatures warm. Two of the tomato races, 2 and 3, have overcome the Ve resistance. This pathogen is long-lived in soils.
Fusarium crown and root rot infected tomato plants show a slow decline over many weeks late-season. A laboratory diagnosis for this disease is important. No cultivars are resistant.
High temperatures can trigger Southern blight. This fungus needs moisture at the soil line to grow. Aegerter said keeping the tops of the beds dry can help with control.
Black mold fruit rot disease is also a late onset disease. Resistant cultivars and timely harvest can reduce damage. Vine trimming to promote airflow is also advised.
