Posts Tagged: walnuts
UC Davis researchers have bred a new walnut variety designed to provide growers a way to harvest earlier and boost the harvest efficiency of California's $1.6 billion walnut industry.
The new “UC Wolfskill” walnut has yield, quality and light color similar to Chandler, which is a late-harvesting walnut and the state's leading variety. UC Wolfskill was bred in 2003 from a cross of Chandler with the Solano walnut. UC Wolfskill combines the color and shell traits of Chandler with the earlier harvest date and kernel fill of Solano.
“The release of UC Wolfskill means growers can spread out their harvest and still have a really high-quality nut that will fetch top-notch prices and provide similar yields,” said Pat J. Brown, breeder and professor with the UC Davis Department of Plant Sciences.
Over 99 percent of the nation's walnuts are grown in California. More than half of the state's bearing acres are the late-harvest Chandler walnuts.
“The California walnut industry needs earlier harvesting walnut varieties to provide efficient use of harvesting, drying and processing equipment,” said breeder Chuck Leslie, with the UC Davis Walnut Improvement Program. “UC Wolfskill can be harvested 12 to 14 days earlier than Chandler and provides consistently light to extra light color.”
Handlers judge the value of a walnut based on its color and how well it halves while processing. In blind quality evaluations by commercial graders, the UC Wolfskill was often not distinguished from Chandler.
UC Wolfskill was originally planted and evaluated at UC Davis, and field trials with growers began in 2011.
“The commitment of our walnut growers, as collaborators, is the foundation that makes this release possible. The Board is extremely grateful for the long-term partnership of our growers and the UC, in finding innovative solutions that help us solve for critical needs,” said Michelle Connelly, executive director of the California Walnut Board.
The California Walnut Board funded the research. UC Wolfskill is currently available to California nurseries for propagation in California and sales to growers throughout the United States. Nurseries interested in propagating and selling this cultivar may obtain a license from UC Davis InnovationAccess.
Outsized wildfires, rising sea levels and disappearing glaciers are dramatic signs of climate change, but not the only ones. New UC Agriculture and Natural Resources research provides forewarning of a change that will be economically and environmentally costly to California – a fifth generation of navel orangeworm, the most destructive pest of almonds, walnuts and pistachios.
Navel orangeworm (NOW) will be more problematic in the future because of warming temperatures, UC Cooperative Extension scientists report in Science of the Total Environment.
Like most insects,NOW's development rate, physiology, behavior and reproduction are highly dependent on the ambient temperature. When the weather warms in the spring, NOW moths emerge from the nuts left in the tree or on the ground during the winter. After mating, females then recycle those last year's nuts to lay eggs and complete one generation. Adults emerged from that first and subsequent generations then lay eggs on in-season hull-splitalmondnuts, where larvae feeding damages the crop. Typically the pests fly three to four times per year – with more flights in areas with warmer weather.
“Warmer temperatures can result in early activity of the pests in the spring and increased activity during the season,” said Tapan Pathak, the UC Cooperative Extension climate change specialist and the study's principle investigator.
The scientists looked at 10 climate models to determine what nut farmers can expect to face over the next 80 years and applied NOW developmental models to the changing climate. Daily maximum and minimum temperature data were obtained for 1950 to 2005, and future projections stretched to 2100.
“The fifth generation can happen in the next few decades,” said Jhalendra Rijal, UC integrated pest management advisor and co-author of the research. “The climate models suggest that spring will begin earlier. That causes insect activity to start earlier. With increased temperatures through the season, the number of days to complete a generation is less. At the end of 2050 or so, we'll see an extra generation.”
The study focused on 23 counties in the Central Valley, from Shasta County in the north to Kern County in the south, where 1.78 million bearing acres of nut crops are planted. About two-thirds of that acreage is planted to almonds, 20% in walnuts and 16% in pistachios. The tree nut crops were valued at more than $8 billion combined in 2018, according to the California Department of Food and Agriculture.
The completion of the NOW life cycle is faster in pistachio compared to almonds and walnuts, so the potential risk of crop damage and economic loss is higher in pistachio, according to the research report. There are only a few years historically in which the models detected the fifth generation of NOW in Kern County pistachios. The occurrence of the fifth generation in almonds and walnuts was historically nonexistent, but it starts appearing in three southern counties by 2040 and eleven counties by 2100.
“In order to alleviate some of the risks related to navel orangeworm damage to nut crops, it is important to implement integrated pest management practices,” Pathak said.
IPM preventative and control measures include sanitizing the orchard during the winter by removing all the nuts on the ground and in the trees, applying synthetic reproductive hormones to limit the pests' ability to find mates, encouraging natural enemies, judicious of least-toxic pesticides if necessary and harvesting the crop early to avoid a new generation of the pest.
“A better understanding of future navel orangeworm pressure on California's major nut crops can help facilitate and strategize integrated pest management practices in order to minimize production risks,” Pathak said.
The results of the research can also inform growers and pest control advisers about the potential increased threat from other pests as the climate changes.
The Community Alliance with Family Farmers and UC Cooperative Extension are working with farmers to establish six demonstration sites in walnut orchards that will examine the effectiveness of mating disruption to control two major pests of the crop – codling moth and navel orangeworm.
The three-year research effort is funded with a $1 million award from the California Department of Agriculture Biologically Integrated Farming Systems program.
“The project sites will be in the Sacramento and northern San Joaquin Valleys, but we expect the demonstration to be of interest to walnut farmers across the state,” said Sara Tiffany, CAFF director of ecological farming and the project lead. “Farmers who grow related crops, like almonds and pistachios, will also be able to benefit from the findings.”
“Farmers need alternatives. In this project, we will be studying the effectiveness of alternatives that already exist,” said Jhalendra Rijal, UC Cooperative Extension integrated pest management advisor for San Joaquin, Stanislaus and Merced counties, the lead scientist on the project. The California Walnut Board is also part of the project team.
Six farmers will be recruited to enroll at least 80 acres each in the demonstrations – three farmers in the Sacramento Valley and three in the northern San Joaquin Valley. The entire acreage will be managed following UC IPM guidelines for walnut production, including cover crops, reduced risk pesticide options and biological control.
Forty acres will be treated with commercially available mating disruption products, while the other 40 acres will not. The treatment works by confusing the pests. Codling moth and navel orangeworm moths naturally release pheromones that help them find mates. The female lays eggs in the immature nuts, and when they hatch, the larvae feed on the nuts, rendering them unmarketable. In the treated area, the orchards will be flooded with a synthetic pheromone that makes it much more difficult for male and female pests to hone in on one another.
Besides codling moth and navel orangeworm, the project will systematically look at the effects of cover crops and predatory mite release on pest mite populations, and improvement in other natural enemy populations in walnut orchards.
The results of the IPM practices will be shared widely with growers, pest control advisors and certified crop consultants in articles, meetings and field days.
“Currently the use of mating disruption in walnuts is significantly lower than in almonds,” said Rijal, who is also the associate director for Agricultural IPM with the UC Statewide IPM Program. “We believe when farmers see the results of using mating disruption, along with other sustainable walnut production practices, we will improve the adoption rate.”
Four staff research associates will join the ranks of UC Cooperative Extension scientists in the coming months to support nut crop advisors conducting critical research in walnut, almond and pistachio production.
The California Walnut Board, the Almond Board of California and the California Pistachio Research Board together have provided about $425,000 to cover annual salaries, benefits, travel and equipment for the new UC Cooperative Extension staff. Under the terms of the agreement, the new positions will be funded annually for up to three years, pending available funds and success of the program.
“By supporting these new positions in UC Cooperative Extension, the California Walnut Board, the Almond Board of California and the California Pistachio Research Board show their recognition for the value of applied research conducted by our nut crop advisors,” said UC Agriculture and Natural Resources vice president Glenda Humiston. “We are grateful to these industry organizations for this vote of confidence and the generous funding to generate science-based knowledge to apply on California farms.”
The new research associates will each devote time supporting two advisors with tree nut assignments:
- Allan Fulton and Luke Milliron, serving Butte, Glenn and Tehama counties
- Katherine Jarvis-Shean and Franz Niederholzer, serving Colusa, Sacramento, Solano, Sutter, Yolo counties
- Mae Culumber and Phoebe Gordon, serving Fresno, Madera and Merced counties
- Elizabeth Fichtner and an advisor under recruitment, serving Tulare and Kings counties
The arrangement reflects a change in how UC Cooperative Extension supports the agriculture industries in California with applied research. With less funding from its traditional revenue sources – USDA, the state government and counties – advisors cover more territory than in the past. Over the years, they have also taken on an increasing share of UC's applied research mission serving the state's specialty crops industries.
The new staff research associate positions were crafted to attract highly qualified candidates who will support advisors' applied research efforts. Their primary focus will be on assisting advisors with planning, execution and gathering data on experimental and demonstration field trials.
UCCE advisor emeritus Joe Grant, who now serves as production research director of the California Walnut Board, chaired an industry working group that drafted the plan based on advisors' input about their needs.
“Advisors are competent and creative people with the skills and knowledge to do research. They need the same support that researchers on campus have,” Grant said.
The California Pistachio Research Board previously provided funding for a plant pathology researcher and an integrated pest management advisor at the UC Kearney Agricultural Research and Extension Center in Parlier. In addition, the board supported creation of $1 million endowments for a nut genetics researcher and a tree nut soil science and plant-water relations researcher as part of an initiative co-funded by UC President Janet Napolitano.
“We've been concerned for a long time about UC Cooperative Extension's research capacity and infrastructure issues,” said Bob Klein, manager of the California Pistachio Research Board. “This new initiative will increase efficiency and productivity for farm advisors and also reduce their stress from being overcommitted.”
Josette Lewis, the Almond Board chief scientific officer, said the organization depends on UCCE farm advisors for unbiased, quality information about almond production.
“Advisors are a valuable link between UC campuses and growers, not only in doing applied research that helps growers thrive, but in meeting California's goals of environmental and social sustainability,” Lewis said. “The information they generate is shared with a host of ag industry professionals – pest control advisers, crop consultants and people in the private sector who provide services to growers.”
Commodity industry funding for UC Cooperative Extension reflects the value the nut crop industries leverage from one of the strongest agricultural research and extension systems in the world, Lewis said.
The new program is modeled after a pilot project in Colusa County in which the Almond Board provided funding for Niederholzer to hire an intern to support almond research. A young scientist who held the post from 2015-16 was Milliron. In 2017, UC Cooperative Extension named Milliron a sustainable orchard systems advisor for Butte, Glenn and Tehama counties and he will now supervise one of the new staff research associates.
“We had a chance to keep him in the system and capitalize on what he learned during his internship,” Lewis said.
There are other tree nut and fruit advisors in need of research help, Grant said. For example, there are concentrations of tree fruit and nut acreage and growers in Kern, San Joaquin and Stanislaus counties.
“We positioned these four research associates where we heard the need for help was most critical. We can see adding another position or two in the future if funds are available,” Grant said.
Across the globe, scientists have shown that birds can be farmer allies. Insectivorous birds feed on damaging insect pests in many crops including coffee, cacao, oil palm, corn, cabbage and apples. Raptors, including hawks and barn owls, feed on rodents, including gophers, voles and mice (see blog, Barn owls help clean up rodents naturally).
Despite this deep historic knowledge that birds are important predators of crop pests, over time the perception of birds as natural enemies of pests has been generally replaced with the idea that birds are often major crop pests themselves. Indeed, some bird species — like some types of insects — can cause trouble for farmers, but many others — especially those that eat insects and rodents — can be beneficial.
Do birds control insect pests on farms in California's Central Valley?
They do! Recent studies by Dr. Sacha Heath, UC Davis, and Rachael Long, field crops and pest management advisor, UC Cooperative Extension, showed that birds help control insect pests in walnut orchards. Dr. Sara Kross (UC Davis postdoctoral alumnus, now with Columbia University) showed that birds help control alfalfa insect pests.
Birds are voracious predators of codling moth pests in walnuts
Codling moth is a major worm-like pest that infests walnuts, apples and pears. The larvae go dormant during winter, living in cocoons in crevices in trees. Adult moths emerge in the spring, lay eggs and infest crops.
We evaluated bird predation of codling moth using “sentinel prey” and exclosure cages. We glued codling moth cocoons to walnut trunks and covered them with cages, allowing insects and spiders to access the cocoons, but not bird predators. This allowed us to count how many larvae were eaten inside and outside of the cages to estimate pest reduction by birds.
What did we find?
Natural enemies, like parasitic wasps and lacewings, alone reduced codling moth larval numbers by 11%; adding birds into the pest control system reduced them by 46%! Nuttall's woodpeckers and white-breasted nuthatches did a lot of the work; these birds travel up and down the trunks of trees, searching for insects.
Above, a white-breasted nuthatch preys on a codling moth larva “sentinel cocoon” on a walnut tree. Video by Sacha Heath.
Alfalfa weevils are no match for insectivorous birds
Alfalfa weevils are key pests of alfalfa, reducing yields and hay quality if left uncontrolled. Dr. Sara Kross looked at bird predation of this pest by excluding birds from alfalfa plants via cages, and counting the number of weevils inside and outside the cages. She found that birds reduced the number of weevils by more than 30%, showing their importance in helping to protect alfalfa from this serious pest.
Does field edge habitat, like hedgerows, help attract beneficial birds?
Yes! Hedgerows are important habitat for beneficial birds, serving as nesting, foraging and roosting sites. In a study in the Sacramento Valley, crop margins with hedgerows, tree lines and riparian buffers harbored up to six times more birds and up to three times more bird species than bare or weedy margins.
Walnut orchards adjacent to hedgerows and riparian areas had higher numbers of beneficial birds along with more species. In alfalfa, there were more beneficial birds in fields when at least two tall trees were present along the field edges. More beneficial birds were associated with better pest control, that is, fewer codling moth cocoons and alfalfa weevils.
Birds have large territories, fly long distances, and are influenced by what happens on the farm as well as by what happens in the landscape around the farm. For example, we found that codling moth predation by birds greatly increased in walnut orchards as the amount of habitat in the landscape around the orchards increased (including hedgerows, tree lines, riparian and oak woodlands, and grasslands).
Will hedgerows increase the numbers of pest birds?
Pest birds are present on farms regardless of field edge habitat (such as weedy vegetation or hedgerows). Cases will be different, depending on the crop, but in the fields and orchards of Yolo County, researcher Hillary White (formerly with UCCE and now with U.S. Fish and Wildlife) found that three of the most common avian crop pests (American crow, red-winged blackbird and Brewer's blackbird), were up to 10 times more abundant in agricultural fields with bare or weedy margins than in fields with hedgerows.
What can I do to attract beneficial birds to my farm?
Our avian research team has been quantifying the conditions under which birds are helpful or harmful to growers. We are looking for ways to help farmers create bird habitat on their farms to harness the beneficial pest control services birds can provide, while also protecting crops from the damaging effects of some bird species. This information is available in the new publication “Supporting Beneficial Birds and Managing Pest Birds,” co-authored by the Wild Farm Alliance and Drs. Kross and Heath, and technically advised by UC Cooperative Extension and several farmers. This is a user-friendly guide for farmers and conservation practitioners, with the goal of co-managing farmlands for biodiversity and farming.
A white-breasted nuthatch preys on a codling moth larva “sentinel cocoon” on a walnut tree. (Video still: Sacha Heath)