Joint research by UC Davis and UC Cooperative Extension will look at  the impact compost applications on young alfalfa fields can contribute to soil health. Sites will include first year alfalfa fields in San Joaquin and Yolo counties.

Michelle Leinfelder-Miles, Delta crops resource management advisor and Rachel Long, field crop integrated pest management advisor in Yolo, Solano and Sacramento counties, along with UC Davis researchers Kate Scow and Radomir Schmidt were awarded funding for this project from CDFA’s Healthy Soils Program. The project will demonstrate compost application to alfalfa fields to improve soil structure and fertility and use practices designed to reduce greenhouse gas emissions and store carbon.

Although many dairies do spread manure on their alfalfa fields, compost is not typically applied during the course of an alfalfa field’s productive life.  Leinfelder-Miles said alfalfa production practices along with heavy clay soils could impair soil physical conditions.

“Physical characteristics of soil can be degraded over time due to high-traffic alfalfa production practices that contribute to soil compaction and poor water infiltration,” Leinfelder-Miles said. Soil health characteristics include fertility, water holding capacity, long term productivity and sustained organic matter content.

This project began with soil sampling at both sites to determine the current status of soil conditions. Compost applications were due to commence this month as the fields were entering winter dormancy. In collaboration with Westside Spreading LLC, the compost applications will be made in the fields. Two treatment rates and a control will be done in each field. Compost will be applied at 3 tons per acre and 6 tons per acre and soil changes will be monitored and compared with the control plots. The compost to be applied is derived from green waste.

According to UCCE’s Alfalfa and Forage News, alfalfa has the ability to take up large amounts of nitrogen and phosphorus from the soil, two components of concern with organic wastes.  With more than half million acres of alfalfa grown in California, proving use of green waste compost to improve soil health could open an organic waste management stream and divert green waste from landfills.

Compost will be applied annually in the fall (2020, 2021, 2022), Leinfelder-Miles said. Soil will be sampled ahead of compost application and then a final soil sample in 2023. They will conduct monthly greenhouse gas monitoring. Alfalfa yields over the course of the study will be monitored.

A robotic pressure chamber that can harvest its own leaf samples and test them on site is being developed by UC Merced Computer Science and Engineering Professor Stefano Carpin, Environmental Engineering professor Joshua Viers and UC Riverside professors Konstantinos Karydis and Amit K. Roy-Chowdhury. These instructors received a $1 million grant from the USDA through the National Science Foundation’s National Robotics Initiative.

Having accurate field data that is updated frequently can help growers plan irrigation frequency and conserve water.

‘If we’re going to use precision agriculture, we need the most accurate information gathering systems we can make,” Carpin said.

One current water status measuring technique calls for leaf sample collection and using a pressure chamber. Karydis explained that mix up of samples, different properties of leaves and time elapsed between pulling the samples and testing them can produce inaccurate data that may negate any water savings. In addition, using hand held instruments in the field can be time and labor intensive and require special training to ensure accuracy of the data.

Carpin has worked with researchers at UC Davis and Berkeley to create RAPID the Robot-Assisted Precision Irrigation Delivery system which travels along rows, adjusting irrigation flows according to sensor data that tells the robot precisely what is needed for each plant.

The same base robot as RAPID will be used in this study, but it will be equipped with GPS and a pressure chamber being designed in Riverside and paired with drones that can survey the field and direct the robot to areas of interest.

The project has four phases: development of the chamber, developing machine vision so the robot can ‘see’ the water coming from the leaf stems; coordinating multiple robots in the air and on the ground and evaluation.

Researchers plan to have the first set of automated pressure chamber prototypes fabricated by Spring 2021 and will evaluate their performance and refine designs in controlled settings over Spring and Summer 2021. They expect to have a completed set up by Winter 2022 and begin controlled field testing.

When all of the components have been designed, the designs and code will be open source and all the data collected during the project will be made available to the scientific community.

The project was initiated after Carpin and Viers spoke with growers about the challenges of growing almonds and grapes. Karydis and Roy-Chowdhury also reported similar conversations with citrus and avocado growers in the Riverside area.

“California agriculture presents a challenge in terms  of scalability,” Carpin said, “but this is an exciting collaboration because we’ll get to develop a system that will work on different kinds of crops.”

New fungicides that provide a new level of efficacy, along with integrated management practices can help California citrus growers deliver high-quality fruit to valuable export markets.

In a Citrus Research Board webinar, UC Riverside plant pathologist Jim Adaskaveg cited pre- and post-harvest diseases that infect citrus fruit when environmental conditions including rainfall favor spread of the fungal pathogens.

“All pre harvest diseases need high rainfall to develop and cause economic damage,” Adaskaveg said.  Most post-harvest diseases have their origins in fruit injuries that allow entry of pathogens, he added.

Two citrus fungal diseases that will keep citrus fruit out of the export market are Septoria spot and Phytopthora.  Infections of Septoria spot begin with injury to the peel. An ice mark due to a freeze event will leave small irregular pitted, shallow lesion on fruit and an entry point for a pathogen. As the infection advances, the lesions become dark and extend into the albedo- the white part of the peel. The disease does not affect the juice quality, but the appearance of the fruit will limit marketing opportunities. S citri, the pathogen that causes Septoria spot, is a quarantine pest in South Korea, a major market for California citrus. Adaskaveg said the Korean market for citrus is maintained through compliance with quarantine measures, following GAPs and fruit certification in the NAVEK program (a joint UC/citrus industry program).

Phytopthora, is a soilborne disease that can affect tree roots, trunk and the fruit. This complex disease can cause tree decline, root rot, brown rot and yield reduction A pre-harvest infection of brown rot is most likely to be found on fruit growing on the lower one-third of the tree as water splashing from rain or irrigation can spread the pathogen up into the tree.

Orientation of the orchard, tree density and skirting are cultural practices that can help keep infections low pre-harvest.  Complementary strategies include pre-harvest fungicide treatments and implementing handling procedures to minimize injury. Planting tolerant rootstocks in areas where Phytopthora infections are common is recommended.

Adaskaveg said new fungicides registered for use in citrus are highly effective in reducing Phytopthora soil populations and root rot as well as improving yields. Two of the new formulations are Orondis and Presidio.

These new fungicide each have a different mode of action and field studies have shown that the active ingredient in these formulations were detected in root, stem and leaf tissues of treated citrus seedlings indicating systemic uptake.

The new fungicides are expected to reduce dependence on fumigation of orchard sites and provide resistance management for sustainable control of Phytopthora.

Following an adverse effect report with imidacloprid, California Department of Pesticide Regulation (CDPR) is reevaluating use of neonicotinoid pesticides to develop mitigation measures to protect pollinators.

As a result of the reevaluation, which included issuance of a pollinator risk determination, CDPR determined that additional mitigation measures are needed to protect pollinators from the use of neonicotinoids in agricultural crops and is developing mitigation measures in the form of regulations.

During two webinars, CDPR shared information on their reevaluation process and gathered feedback on the proposed pollinator protection mitigation measures for the use of nitroguanidine-substituted neonicotinoids in agricultural crops. The original comment period has been extended. Comments and feedback on the proposal will now be accepted until the end of day on October 30, 2020. Comments can be made by e-mail to neonics@cdpr.ca.gov or by leaving a voicemail message at 916-445-0003.

CDPR is looking for feedback on extent of mitigation, organization and clarity, ratings and timings, efficacy against pests, impacts for critical uses and alternative approaches.

CDPR proposals include development of regulations to mitigate risks to bees and pesticide residue and honeybee toxicity studies. Other considerations include current pest management practices, critical pest issues, resistance management and level of pollinator exposure. The agency is taking a multi-level approach determining crops that are highly attractive to bees, crops that are moderately attractive to bees and crops that are not attracted to bees.

For more information on neonicotinoid reevaluation or view the current semiannual report summarizing reevaluation status visit the Cal DPR  Reevaluation Program page. To provide comments click this DPR email link.

CDPR reports they will continue to meet with stakeholders. Draft regulations are anticipated to be posted by end of the year.

A parasitic weed, branched broomrape, has recently reemerged in California processing tomato fields. The weed uses a modified root called haustorium to fuse into a host plant root and extract nutrients and water.

The UC Weed Science newsletter reported branched broomrape is causing concern among tomato growers as infestations in other tomato growing regions have shown vulnerability of the crop. This weed seems likely to establish and spread in California due to the similarity to the species’ native climate. Limited crop rotation and a wide range of hosts, including carrot, sunflower and safflower, may also contribute to spread of this weed. It can be spread via machinery or irrigation water, and the tiny seed is long lived in the soil, allowing it to persist in the absence of host plants. The major portion of the parasitic weed’s life span is underground, making it inaccessible to cultivation or contact herbicides.

UCCE vegetable crop advisor Amber Vinchesi-Vahl said that there are currently no herbicides registered in California for tomatoes to control branched broomrape.

The short-term goal is to minimize spread of broomrape, Vinchesi-Vahl said. Next steps will be to develop mitigation measures.

There was a severe infestation of branched broomrape in the Sacramento Valley in 1959, and fumigation with methyl bromide was used to kill the soil seedbank. Eradication efforts from 1973 to 1982 involved intensive field surveys and fumigation of infested fields. Reintroduction or recurrence from long dormant seed in the soil and subsequent spread have been speculated as cause of reemergence.

Branched broomrape is classified in California as an ‘A’ pest, an organism of known economic importance, and is subject to enforced action including eradication, quarantine, regulation, containment, rejection or other holding action. At this time, discovery of a branched broomrape infestation in a commercial processing tomato field will result in a hold order and crop destruction without harvest.

Infestations of the Q-listed Egyptian broomrape in California is also causing concern in the processing tomato industry. The Q listing is a temporary ‘A’ classification pending determination of permanent rating by the state.

Counties reporting branched broomrape detections include Colusa, Sacramento, San Benito, Santa Clara, San Joaquin, Ventura and Yolo.

Studies in Israel and Turkey showed that extreme infestation levels of branched broomrape could cause yield losses as high as 70%. Chile has reported 80% crop losses due to branched broomrape infestation in tomato fields.

The threat posed by many invasive insect species to California agriculture is accelerating, reports UC Riverside’s Mark Hoddle, who believes proactive biological control could be the key to averting disaster.

Non-native invertebrates (e.g. insects, mites, mollusks, etc.) are establishing in California at the rate of nearly 10 per year. Trade and tourism are major drivers in movement of exotic invasive species worldwide, Hoddle said, and live plant imports are a major conduit for pest and pathogen movement into and throughout the U.S. Prior to 1989, Hoddle said, California acquired around six new exotic arthropod species a year. For the time period 1989-2010, that number increased to nearly ten new exotics detected each year.

The group of insect invasive species most likely to invade California and threaten agriculture include sap feeders such as aphids, psyllids, mealybugs and whiteflies.

Should California have been better prepared for the Asian citrus psyllid? Hoddle asked in an Ask The Expert UC webinar. With the knowledge that ACP and the bacterium known to cause Huanglongbing were in Florida, Texas and Mexico, the approach by California was reactive rather than proactive, he said. ACP spread rapidly once in California and large populations resulted. When dealing with a predictable invasion threat, Hoddle proposed a more disruptive approach to managing invasive species, getting ahead of an obvious problem before it happens.

For example, it took nearly 10 years to run a biocontrol program targeting ACP in California. This program didn’t start until the invasion of California by ACP was well underway; it was a reactive approach. During this time, colleagues in Pakistan were contacted for foreign exploration efforts, and time was needed to collect, identify, screen and raise and mass-release host-specific parasitoids that can suppress ACP populations in California, Hoddle said.

A proactive approach would involve identifying and collecting natural enemies, maintaining colonies in quarantine and running host specificity and host range tests, and prepare a report for USDA-APHIS review in advance of the anticipated invasion of the target pest. Detection of the first established non-eradicable pest population would initiate the biocontrol program against the target pest. This proactive response would save years of time and allow a rapid, almost immediate, response to managing the pest with biocontrol agents.

The concept of proactive biocontrol is simple: Have natural enemies ready before the anticipated pest invasion occurs. Had the parasitoid for ACP been identified and ready, much economic and environmental impact could have been avoided. For example, there has been about a 70% decline in ACP numbers after the biocontrol program started. Could this suppression have been achieved earlier and the spread of ACP slowed if the ACP biocontrol program had been proactive instead of reactive?

Spotted lantern fly is a good target for proactive biocontrol, Hoddle said. This prolific and highly polyphagous insect is expected to arrive and establish in California and poses a threat to vineyard and tree nut crops. Spotted lantern fly infestations in Pennsylvania have killed vineyards, removing sap and leaving the vines vulnerable to winter cold. In South Korea, where spotted lantern fly has become established, it is a known pest in walnuts.

Hoddle recommends being proactive about identifying potential invasive species and developing a management plan before they arrive. A proactive program targeting spotted lantern fly is currently underway in quarantine at UC Riverside where the safety of an egg parasitoid imported from China (the native range of SLF) by the USDA is currently being assessed.

While the concept of integrated pest management (IPM) is not new, current economic considerations in almond production make these practices even more important.

UCCE Orchard Systems Advisor Franz Niederholzer said the goal of IPM is long-term pest management with economic sustainability.

“It’s a buyer’s market now, and buyers are increasingly asking about sustainable production practices.” Niederholzer said. “IPM is a key part of sustainable management.

“This is why it is even more important to re-consider and review IPM practices. The goal is to end the season in the ‘black’, with the best chance of staying there for years to come.”

IPM is a pest management strategy that first uses cultural and biological control practices followed, where needed, by careful, measured, strategic response to known pest pressure. The cultural & biological control practices work in the background, providing a safety net if active treatment does not deliver the desired pest control.

Planting decisions are key to long-term orchard health. Disease tolerant rootstocks, adequate soil drainage and planting direction make a difference in orchard health and performance.

Key practices for a strong IPM program during a growing season include: 1) Monitoring pest populations regularly, basing timely spray treatments on economic thresholds (where known) and 2) Careful spraying with materials selected to control the specific pest(s) and limit harm to non-target organisms.

Targeting diseases, Niederholzer said Sacramento Valley almond growers have less flexibility in fungicide programs due to higher disease risk under wetter conditions common in the northernmost almond growing region of the state. The best disease control is usually achieved with fungicides applied before rainfall. Focus on effective disease control early in the growing season when good spray coverage is easier to achieve and before symptoms appear. Information developed by UC plant pathologists (Adaskaveg, Gubler, Michailides) listing fungicides (conventional and organic,) their efficacy and key use timings is available at UC IPM.

Insect control with IPM can be challenging, especially for pests with limited biological control options including navel orangeworm (NOW) and leaffooted bugs. Cultural control practices including orchard sanitation and harvest timing are key to NOW control in a solid IPM program.

“You can’t spray your way out of long-term problems. Cultural and biological control practices in an IPM program are critical to effective pest control and delivering a product the market wants,” Niederholzer said.

Suterra’s aerosol puffers that dispense pheromones for mating disruption in California tree nut, stone and pome fruit orchards will have a different look starting this season.

Zak Clark, senior manager for engineering and quality at Bend, Ore.-based Suterra, described some of the improvements made in their puffers to improve durability and performance.

“We worked to make these stand up to the orchard environment, so growers could depend that they were working throughout the season,” Clark said.

Suterra has been making aerosol puffers and their own cans for over 10 years. Clark said they have been collecting, diagnosing and refurbishing puffers for almost that long, and in the process determining how to make them better.

“The goal is to get the pheromone out at the right dose at the right time, regardless of environmental conditions,” Clark said. “We want a precision dose for every shot it makes throughout the season.

“We consider it a catastrophe if the can empties early or doesn’t deploy at all due to clogging or mechanical defects. That is not acceptable.”

Clark said the gear train will deliver puffs for an entire season with only 2 AA batteries that can withstand environmental conditions including heat.

The dispersing device is a key component in the puffers and Clark said the aim was to make them lighter in weight, with a sealed compartment and a one-step power on feature. The technology includes a patented cam drive for dispensing, and a thermostat to make sure pheromone is released at the right temperature. The sealed compartment protects the electronics and gear from heavy rain, residues and dust. The sealed head unit prevents jams and friction from contaminants.

In addition to improved durability, there is now a single button to simplify deployment. The device is also lighter and uses 60 percent less plastic. The lighter weight allows for more movement in the tree canopy to reduce drop. Growers will get a new unit every year, with spent devices recycled at the customer’s convenience.

The new design will be applied to all Suterra’s Puffer products in California, including NOW-Ace, CM-O Pro, OFM-O, and CM/OFM Pro. The pheromone formulation and application rates are the same as previous seasons. The product itself has not changed, the performance and ease of the dispersion vehicle has, Clark said.

Resistance to glyphosate, paraquat and ACCase inhibiting herbicides has been confirmed in Italian ryegrass, a major weed in California orchards, vineyards, field crops and fallow fields.

Control of Italian ryegrass had been achieved with several different herbicides until resistance evolved with repeated use. Resistance to multiple post-emergent herbicides with different modes of action has also been confirmed within the same orchard, vineyard or field in some areas.

Dr. Marie Jasieniuk, associate professor in the UC Davis Department of Plant Sciences wrote in a Weed Science blog that glufosinate is an alternative non-selective post-emergence herbicide that can still be used to control herbicide–susceptible and most herbicide-resistant Italian ryegrass in California as only two populations with resistance to glufosinate have been documented.

Glufosinate-ammonium is a contact herbicide that works by inhibiting an enzyme central to plant metabolism. Plants absorb this substance primarily through their leaves and other green parts.

Jasieniuk noted that the higher cost of glufosinate relative to other herbicides may drive lower use rates. The lower rates and other drivers including herbicide applications at non-optimal weed size, inappropriate weather conditions and insufficient spray coverage may result in sublethal rate selection of ryegrass by glufosinate.

Jasieniuk conducted a greenhouse study to evaluate the potential for low glufosinate rates to select for reduced susceptibility to the herbicide and to determine if selected populations are cross-resistant to herbicides with other modes of action.

The study was conducted with an herbicide susceptible parent population collected from a Sonoma County vineyard. Plants were grown in the greenhouse to the 3-4 leaf stage and treated with low glufosinate rates for three generations.

To evaluate the potential for low glufosinate rates to select for reduced susceptibility to the herbicide, and to determine if selected populations are cross-resistant to herbicides with other modes of action as has been observed in a few studies, Jasieniuk conducted a greenhouse study using an herbicide-susceptible parent population originally collected from a vineyard in Sonoma County. Plants were grown in the greenhouse to the 3- to 4-leaf stage and treated with low glufosinate rates for three generations.

In the first round of treatments, the plants were treated with glufosinate at one-eighth, one quarter and one half of the labeled field rate. Surviving plants were grown to reproductive maturity and allowed to cross–pollinate. Seeds were harvested from all plants pooled and germinated. Plants in this second generation were treated at slightly higher rates at one-half, three-fourths and the labeled rate. For the third round the treatments were three quarters, the labeled rate and one and a quarter of the labeled rate.

Results showed that susceptibility to glufosinate was reduced in offspring in comparison with the susceptible parent population following only three generations of selection.

The study showed that repeated selection with glufosinate at low rates can reduce the susceptibility of Italian ryegrass populations to glufosinate, and points to the importance of incorporating a diversity of approaches, both chemical and non-chemical, in the management of ryegrass in annual and perennial cropping systems of California.

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.