Choosing the right seed to match the site and goals is key to getting desired benefits from a cover crop in nut orchards, according to speakers during a California Alliance for Family Famers webinar that focused on cover cropping in tree nut orchards.

Organic walnut grower Sean McNamara of Winters reported on his challenges and successes with choosing a cover crop seed mix, planting and stand establishment in his orchards.

McNamara said changes were necessary in orchard management to have a successful cover crop, but there were also some cover crop decisions made to match his management system.

As an organic grower, McNamara said nitrogen fixation was an important goal for his cover crops. He also wanted to mitigate soil compaction and add diversity to the seed mix. What he did not want was a lot of biomass in the orchard at the end of the growing season.

“With those parameters in mind, he also noted “if you can’t get it to grow, it is a waste of time and money.”

He advised paying attention to not just ratios of seed in mix, but also seeds by weight. Grass seed can overwhelm the cover crop mix due much higher numbers of seed per pound.

Kamprath Seeds representative Tom Johnson provided his ‘decision tree’ for choosing a cover crop. The ‘right’ one for a specific grower and orchard takes into consideration the orchard age, soil type, depth and infiltration rate. Rainfall amounts for germination, slope of the ground and available equipment are other factors. Grower or manager expertise with cover crops and the time available for management also play a role in cover crop seed selection.

Johnson covered reasons to plant a cover crop in an orchard and choosing a system that fits time and management capabilities.

“My advice is to start slow and simple, you can make it as complicated as you want later,” Johnson said. No one crop mix will deliver all the results desired, he said.

The main issue in the orchard that a grower wants to address with a cover crop will determine the seed mix and system that will work best.

An example is a crop planted to improve water infiltration. Brassicas and small grains grown in a plow down system would achieve that goal. A solution for nutrient management could be a legume mix with annual reseeding.

Wendy Rash with the Natural Resources Conservation Service presented information on the eVeg Guide on the NRCS website. The current map data gives information on suitability for seed mixes at valley locations. The site also includes a model for developing a cover crop seed mix, compatibility information and warnings for seed choices.

Additional resources for growers include CAFF’s Cover Crop Webpage, NRCS EQIP program and Project Apis m.’s Seeds for Bees program.

Development and introduction of new, high quality and disease-resistant cultivars in almonds, apricots, table and raisin grape varieties is the goal of USDA’s Crop Diseases, Pests and Genetics Research team in the Parlier research facility.

In its annual report, the team announced five-year goals to enhance breeding efficiency for table grape fruit quality and other priority traits by identifying associated molecular markers and through trials to determine their commercial use and map fruit traits related to flowering time, rachis structure and berry size. The research includes identifying sources of resistance and to develop molecular markers associated with resistance to Botrytis cinerea, powdery mildew and Pierce’s disease. Advanced table grape selections will be compared for production timing and fruit quality after cold storage with existing table grape cultivars.

Prunus development will focus on high-yielding, self-compatible almond varieties and glabrous-skinned or smooth skin apricot. Hybridizations will be performed to identify and select new almond varieties that are California adapted, early ripening and also have nonpareil-like kernel characteristics. Newly available glabrous skinned apricot accessions from Kyrgyzstan will be propagated when available from plant protective quarantine and used in hybridizations to assist with the breeding effort.

In almonds, hybridizations have been performed among self-fertile selections having nonpareil shaped kernels. A research-sized roller-cracker provides data on kernel durability at harvest. Multivariate kernel analyses are being used to identify new selections with nonpareil-shaped kernels.

Glabrous skin apricot imported to the U.S in the 1990s have been hybridized with California adapted apricots, but the initial crosses had no glabrous skin offspring. When the first generation was crossed amongst themselves, 25 percent of the offspring produced glabrous skin fruit. These crosses are being evaluated for fruit quality characteristics and ranked for use as parents. Fruit size and detrimental skin characteristics were listed as main concerns along with small fruit size. Neutral flavor skins predominate in apricots, but the glabrous skin apricots can exhibit both acidic and astringent skin flavors. Current fruit evaluations of the glabrous skin accessions will identify the largest fruited crosses having neutral skin flavor for use in planned crosses.

Agriculture Research Service researchers in Parlier have announced the release of a new early season table grape variety that has both exceptional eating quality and reduced cultural input needs. Solbrio has a large berry size, a crisp texture and full color. Many of the standard cultural practices used to enhance these characteristics in other table grape varieties are not necessary with Solbrio, ARS researchers report.

Discovery of the first substance capable of controlling citrus greening disease or Huanglongbing was recently announced by UC Riverside.

According to UC Riverside, a naturally occurring molecule found in Australian finger limes, an antimicrobial peptide, is more effective in treating the disease than the antibiotics currently in use in Florida.

UCR geneticist Dr. Hailing Jin said that, unlike the antibiotic sprays, this peptide is stable even in high temperatures. Florida citrus growers have been using antibiotic sprays in an attempt to save their trees from the CLas bacterium that causes citrus greening.

Dr. Jin isolated the genes from the finger lime that contribute to the bacterial immunity. One of the genes produces the peptide which was tested over a two-year time span.  She said the peptide is applied to the trees a few times per year to control citrus greening. The material can be applied by injection or foliar spray and it moves systemically through plants and remains stable, making the effect of the treatment stronger.

The California citrus industry has been focused on suppression of the Asian citrus psyllid, a vector of citrus greening, as the infection has not been found in commercial citrus production in the San Joaquin Valley.

Some of Dr. Jin’s research was funded in 2018-19 by the Citrus Research Board. The study was conducted within the UC Davis Contained Research Facility on year-old Madam Vinous, Washington Navel and Lisbon lemon plants that were treated through either foliar sprays or pneumatic injections.

CRB’s initial $100,000 investment in this research was supplemented by a nearly $4 million grant from the USDA National Institute of Food and Agriculture. USDA-NIFA funding for this phase went into effect in February of last year and is scheduled to continue through January 2023.

The long-term effectiveness of this treatment has not been confirmed or published in a scientific journal and the project is still in its early stages. Dr. Jin’s promising findings have resulted in a commercial licensing agreement between UCR and Invaio Sciences. In this case, more work still needs to be done to confirm the robustness and viability of this treatment. Additional greenhouse trials are being initiated by Dr. Jin and her team at the citrus-specific Bio-Safety Level-3 Laboratory in Riverside, California. It also is expected that field trials will be conducted to show the effectiveness of the treatment under commercial grove conditions.

The need for a citrus greening disease cure is a global problem, but hits especially close to home as California produces 80 percent of all fresh citrus in the United States, said Brian Suh, director of technology commercialization in UCR’s Office of Technology Partnerships, which helps bring university technology to market for the benefit of society through licenses, partnerships, and startup companies.

“This license to Invaio opens up the opportunity for a product to get to market faster,” Suh said. “Cutting edge research from UCR, like the peptide identified by Dr. Jin, has a tremendous amount of commercial potential and can transform the trajectory of real-world problems with these innovative solutions.”

Pests are out in full force. Protect your crops this summer with the addition of an adjuvant that can double the potential of your insecticide. Using technology that reduces evaporation and keeps tank mix droplets on the target in a liquid state twice as long as a typical surfactant, OMRI listed Ampersand® adjuvant gets more of your tank mix to the leaf and keeps it there longer, giving your insecticide time to perform its function. Learn more at www.attuneag.com

Weekly ET rates are available online on the Sac Valley Orchards website along with information on how to use the reports. UCCE irrigation resources Farm Advisor Allan Fulton explained that the weekly tables provide real-time estimates of crop ET for crops with approximately 70 percent or more midday canopy shading. The weekly reports provide both crop ET estimates not adjusted for irrigation system efficiency and adjusted for 70-, 80- and 90-percent irrigation efficiency.

Measurement of applied water and understanding of the irrigation system performance are necessary to use these weekly reports. Knowing how closely the amount of irrigation water plus rainfall matches estimates of real-time orchard ET can help make irrigation scheduling decisions, especially if this information is teamed with measurements of tree water status with a pressure chamber or with soil moisture monitoring.

Using weather-based evapotranspiration rates as a guide for irrigating young orchards can be a helpful water management tool, but adjustments will be needed as most published rates of water demands are for mature trees (about five years and older.)

In a video tutorial, Fulton explained that ET rates should be adjusted for tree size and irrigation efficiency. Soil variability and irrigation system performance should also be taken into account when making irrigation management decisions for young trees.

Irrigation management in young orchards can be challenging due to the expanding tree canopies and root systems from planting up to production. Young orchards, while not yet yielding much crop, are using water and nutrients to grow. Expanding leaf area means more leaves with stomata to transpire water and take in carbon. As roots grow, they may also access additional soil moisture other than from irrigation.

Smaller trees have lower ET rates, Fulton said. The question is how much lower and how does it change as the trees grow? Older research has shown that once first leaf trees are established and growing well, almonds may require on average about 40 percent of the ET rate for a mature tree over the course of the first season. More recent research in almonds with lysimeters suggests these older research based estimates may even be conservative (a bit low.) First leaf walnut tree water demand is on average 30 percent of the ET rate for a mature walnut tree. By the fourth year, demand by an almond tree is 90 percent of the ET rate for a mature tree. In walnuts, fourth year trees are on par with a mature tree especially if vegetation in the orchard middles is growing.

Many factors can influence how a young orchard develops ranging from previous crop if it is an orchard replant situation, soils and site preparation, planting date, the source of the new trees, nutrition, and weed competition. As a result, a more advanced and site-specific approach to adjusting ET based on field measurement of canopy shading may interest growers.

Examples of how to specifically adjust the weekly reported estimates of crop ET for mature almond, walnut and other tree crops for younger developing orchards will be provided in an upcoming video series that should be posted in July or August 2020 at the Sacramento Valley Orchard Source website. It is also covered in the Almond Board’s Irrigation Continuum https://www.almonds.com/almond-industry/orchard-management/water-and-irrigation

Five Romaine lettuce varieties that brown less quickly and are slower to deteriorate postharvest have been identified by Agricultural Research Service scientists.

In determining the genetic basis for deterioration, the researchers have identified the location of genes associated with postharvest deterioration of fresh cut lettuce and are in the process of identifying genes associated with browning—two economically important traits. This work will accelerate development of new Romaine varieties with better shelf life as lettuce breeders will be able to check that offspring carry these genes without needing to grow out and test for browning and deterioration resistance.

Lettuces are the most popular commercially produced leafy vegetable in the world and one of the top 10 most valuable crops in the United States. One of the main challenges with this crop is that it is highly perishable.

Having the molecular markers means that slow deterioration and eventually less browning can be more easily integrated into lettuce breeding. The inability to evaluate for deterioration has been an impediment to breeding advances, said study leader Ivan Simko, ARS Crop Improvement and Protection Research Unit in Salinas.

When you consider browning and deterioration ratings together, the best breeding lines for commercial production and also for use as parents to develop new varieties are (in alphabetic order): Darkland, Green Towers, Hearts Delight, Parris Island Cos, and SM13-R2, which is a breeding line developed at the ARS lab in Salinas.

In addition, the researchers found the chromosome region that contains the genes for slow deterioration also contains four genes (Dm4, Dm7, Dm11, and Dm44) and one DNA region (qDm4.2) that codes for resistance to downy mildew—one of the costliest lettuce diseases.

This colocation indicates a strong linkage between one or more of the four genes and the rate of deterioration. DNA-based markers can be used to develop new breeding lines with slow rate of deterioration and desirable combinations of resistance genes. Deterioration is the rupture of cells within lettuce leaves, leading to waterlogging and the lettuce turning to mush. Browning is the discoloration of the edges of lettuce after cutting or tearing. Either development can spoil the leafy vegetable’s value by decreasing shelf life.

In an effort to control browning and prolong shelf life, lettuce processors have been turning to modified atmosphere packaging and flushing bags of cut lettuce with nitrogen gas to reduce oxygen levels in the bags.

These practices are expensive and can lead to other problems such as off-odors and, when coupled with high storage temperatures, anaerobic bacteria growth on the bagged lettuce.

The Argentine ant, or Linepithema humile, is a coffee bean-colored ant native to South America. Introduced in the early 1900s in California likely by exports, the ant has long been a problem for pest management in citrus orchards.

Mark Hoddle, UCCE Entomology Specialist at UC Riverside, spoke about issues surrounding Argentine ants, their mutualistic behavior with sap-sucking pests, monitoring tools, control options and field studies in a webinar presented by UC ANR.

“There are queens, males, workers and brood in underground colonies,” Hoddle said. “Their lifecycles are similar to butterflies, having egg, larval and pupal stages, and about 75 days to develop from egg to adult.”

The sheer number of Argentine ants that make up a colony, as well as their aggressive nature, makes them a daunting species to deal with. Each nest has multiple queens, which typically lay 20 to 30 eggs per day and have been found to lay up to 50 to 60 eggs in certain instances, according to Hoddle.

The mutualistic behavior of Argentine ants, however, is where the real issue lies in citrus orchards. The ants are able to co-exist with multiple sap-sucking, economically damaging pests in citrus such as mealybugs, aphids, whiteflies, soft scales and psyllids. Basically, ants living in orchards tend and feed off honey dew, a sugary excrement produced by these pests. In return, the ants protect their “livestock” from parasitoids and predators, the natural enemies that attack these pests and control their populations.

“They [ants] are specialized liquid feeders that feed on the sugary waste product excreted by phloem feeding pests,” Hoddle said. “Honey dew removal by Argentine ants actually protects these pest populations from essentially drowning in their own excrement, promoting population growth and driving ant infestation severity.”

Hoddle and his research team have been using a variety of monitoring tools to estimate ant densities in citrus orchards, an important way to determine control decisions. Among the monitoring tools used are sugar vials with 25% sucrose solution, counting ants moving past “landmarks”, and a new tool: infrared sensors attached to irrigation piping.

“Monitoring vials often overestimate ant populations,” Hoddle said. “Marking spots on a [citrus] tree and counting ant traffic over a specific amount of time can give good estimates to the densities and activity levels in trees.”

According to Hoddle, irrigation piping tends to be the easiest place to find Argentine ants in an orchard. The ants prefer moving in straight lines on the smooth surface of the piping which enables them to move more rapidly from nests to food sources and back again.

“Infrared sensors along irrigation piping collect physical data and send it to the cloud where the data are summarized and viewable with an app on a smart device,” Hoddle said. “The goal is to create a fully automated ant monitoring system for growers.”

Once the results can give an accurate idea of ant activity in an orchard, control options need to be decided. The most basic option is a physical barrier around the trunk of the tree. Composted organic mulch at the base of trees can deter ant walking speeds due to uneven terrain. Bait stations loaded with 25% sucrose water and ultra-low concentrations of insecticide (.0001%) can also be used.

In a field study completed by Hoddle and his research team, bait stations were used in six navel groves in Southern California where Argentine ants are most abundant. The results showed very quick diminished numbers of ants, with 50 percent reductions over the first month and 88 percent reductions over the next 11 months.

“The bait stations can work, but they need to be taken care of, monitored and replenished regularly,” Dr. Hoddle said. “Biodegradable hydrogel beads made out of seaweed, 25% sucrose water and .0001% insecticide proved effective as well. The ants feed off of these, return the toxin to the nest, and through communal food sharing the workers and queens are slowly poisoned.”

Ultraviolet (UV) light lamps attached to unmanned vehicles are being used to fight powdery mildew infections on research vineyards on the East Coast and may hold promise for West Coast vineyards as well.

Researchers at Cornell AgriTech in Geneva, NY, in collaboration with colleagues at Rensselaer Polytechnic Institute’s Lighting Research Center (RPI-LRC), the University of Florida, and the National Agricultural University of Norway (NMBU), have been working with a Norwegian manufacturer (SAGA Robotics) to develop the autonomous robots for commercial use.

Everywhere grapes are grown, powdery mildew poses a threat to the crop. This fungal disease is especially significant due to cost of control. According to the Robert Mondavi Institute Center for Wine Economics at UC Davis, powdery mildew management accounts for 74 percent of total pesticide applications by California grape growers and 17 percent of total pesticide use in California agriculture (by weight of active ingredient.)

David Gadoury, senior research associate in the Department of Plant Pathology at Cornell AgriTech, who is leading the project, said in a phone interview that interest in this unique control is high in California.

The UV lights are the same germicidal lamps used in hospitals; the lights penetrate plant canopies to reach and suppress certain pathogens. Research in using UV light to kill the powdery mildew pathogens is not new, Gadoury said, but it has accelerated with the discovery that it is effective at night.

He explained that powdery mildews have co-evolved with the plants they attack over millions of years and often develop resistance to chemical treatments. Their evolution has also given them an Achilles heel: adaptation to natural cycles of light and dark. UV light damages DNA of many organisms, but they evolved developed biochemical defenses against this damage, using a repair process that requires the blue light component of sunlight.

“What makes it possible for us to use UV to control these plant pathogens is we apply it at night,” Gadoury said. “At night, the pathogens don’t receive blue light and the DNA repair mechanism isn’t working.”

In field trials, the light arrays are carried within a tunnel-shaped frame that can be adapted to different trellis systems. The robotic factor can be a labor-saving feature, but the lamp array could also be pulled by tractor.

Gadoury said the UV treatment requires four hours of darkness after application for maximum effectiveness. At a speed of 5 mph, a towable or robotic array could travel over 20 miles during the available nighttime, even during the shortest nights of summer in most viticulture areas. Extensive trials have been completed on Florida and California strawberries.  Grape trials for suppression of both powdery and downy mildew are underway in New York, Washington, and Oregon, with California trials planned for 2021.

The research group includes assistant professors Katie Gold and Yu Jiang at Cornell AgriTech, Natalia Peres at the University of Florida, Mark Rea at Rensselaer Polytechnic Institute’s Lighting Research Center, and Arne Stensvand at Norway’s Institute of Bioeconomy.

The research is supported by grants from the USDA-SCRI, USDA-OREI, the Research Council of Norway and the New York Farm Viability Institute. Support also came from lighting companies OSRAM and the Asahi Glass Co.