- Author: Pamela Kan-Rice
UC study predicts three major pests to emerge earlier, produce more generations
As a result of climate change, the Golden State's farms are expected to face a surge in agricultural pests, which poses a threat to California's specialty crops industry. Populations of three major insect pests – codling moth, peach twig borer and oriental fruit moth — are projected to increase mainly due to rising temperatures, according to a study recently published in the journal “Science of the Total Environment” by a team of researchers at University of California Agriculture and Natural Resources and the U.S. Department of Agriculture California Climate Hub.
“These three pests are notorious for infesting most of the walnut, almond and peach orchards of California, causing extensive damages by reducing quality of fruits and nuts,” said study co-author Jhalendra Rijal, UC Cooperative Extension integrated pest management advisor and entomologist for Stanislaus, San Joaquin and Merced counties.
Climate change can lead to shifts in the timing of seasons, including warmer winters, earlier springs and hotter summers, and these conditions can disrupt the natural life cycles of pests.
The California research is supported in part by USDA's National Institute of Food and Agriculture. NIFA National Program Leader Amy Ganguli said the California project is a strong example of the work being done through AFRI's Extension, Education & USDA Climate Hubs Partnership.
“A key element of this grant program to link critical research findings like this with timely education and outreach efforts to producers and the public to encourage nimble responses to the challenges climate change pose,” Ganguli said.
The new research, led by Prakash Jha, UC Agriculture and Natural Resources assistant project scientist based at UC Merced, compared pest populations in recent and future climates. The scientists used temperature projections from the latest generations of scientific models to predict the potential impact of climate change on codling moth (Cydia pomonella), peach twig borer (Anarsia lineatella) and oriental fruit moth (Grapholita molesta). Before using the model, the model predictions were verified using field data of these insect pests from various parts of the Central Valley.
The UC study revealed that due to increases in temperature, these insects are expected to appear up to 28 days earlier in the spring and the time between generations is expected to shorten by up to 19 days. The changes may be gradual, but the study predicts that we may see up to a half-generation of these pests added within the next 20 to 30 years.
The increase in these pest populations poses a serious threat for future pest management, which would subsequently affect the state's economy and employment related to specialty crops, warns Rijal.
“Codling moth is the primary pest of California's walnuts, which occupies over 365,000 acres,” Rijal said. “Similarly, peach twig borer and oriental fruit moth are two major economic pests of peaches. Growers must control almost every generation of these pests to protect the fruit.
“Additional generations of these pests within the same growing season will likely increase crop damage. It certainly increases the number of sprays needed to control these pests, increasing the production cost for growers. Plus, more use of insecticides has consequences for beneficial insects and the environment.”
Growers may need to adapt their pest management strategies to address the impact of climate change on these pests.
For years, the UC Integrated Pest Management guidelines have suggested putting oriental fruit moth traps out in peach orchards by Feb. 15 in the San Joaquin Valley and Feb. 20 in the Sacramento Valley.
“In the last seven years, likely due to warmer winter, as suggested in this study, we observed the beginning of the moth's activity in traps (also called biofix) as early as Feb. 14,” Rijal said, “meaning that the trap placement date must move earlier to capture the first moth activity. We are revising the guidelines to change the trap placement date to Feb. 7 for the entire Central Valley.”
Developing a holistic climate-smart pest management strategy will build resilience, Jha said. This approach combines pest control with prevention and reduction, such as planting pest-resistant crop varieties, sanitizing the orchards during the winter, harvesting early to avoid later pest generation infestation, using biological control such as natural enemies, and deploying mating disruption techniques.
“More importantly, adoption of pest forecasting – including the long-term prediction and short-term potential outbreak, pest-scouting and early detection – will be essential to combat the growing threat posed by these pests,” Jha said.
Research will be crucial to provide growers support and guidance about the latest developments in pest management and how to adapt their practices.
“Climate change impacts on pests and resulting impacts on agricultural production are significant but not often researched or quantified,” said Tapan Pathak, UC Cooperative Extension specialist in climate adaptation in agriculture based at UC Merced.
“Information from this research will not only help farmers to understand impacts for strategic planning, but also will inform the agricultural industry to invest in making varieties more resilient to these damaging agricultural pests,” Pathak added. “We will use this information to update the CalAgroClimate tool, which informs farmers on the progress of these pests during the season so that they can take steps for effective pest management.”
Ganguli added the partnership between the University of California and the California Climate Hub embodies the goal of this funding program.
“The incorporation of this research into the existing CalAgroClimate decision support tool accelerates the ability of this information to be publicly used in the development of appropriate pest management or adaptation strategies,” she said.
In addition to Jha, Rijal and Pathak, the study was co-authored by Ning Zhang, Lauren E. Parker and Steven Ostoja of UC Davis Institute of the Environment and U.S. Department of Agriculture California Climate Hub.
The article “Climate change impacts on insect pests for high value specialty crops in California” can be accessed for free online at https://doi.org/10.1016/j.scitotenv.2023.167605.
Dec. 8, 2023: This story was updated to add comments by NIFA National Program Leader Amy Ganguli.
- Author: Trina Kleist, UC Davis Department of Plant Sciences
Crisosto and team publish handbook for growing peaches and maintaining quality for canning
In an experimental orchard a few miles west of the UC Davis campus, Thomas Gradziel plucked a nearly ripe nectarine from one of the trees. He whipped out a pocketknife and sliced off juicy chunks for Carlos Crisosto to taste. Both are orchard crops experts in the UC Davis Department of Plant Sciences, and both love peaches.
The two made appreciative sounds as they pulled the fruit's flavor across their palates, discussed how this nectarine variety compared to other varieties, and quickly turned to details of production and orchard management.
Peach gives growers basic information that can reduce their production risks, boost profits and help them face issues such as climate change and a shifting world market, CABI writes in the book's description.
“This will still be the definitive text for probably the next 20 years,” said Carlos Crisosto, who is one of the book's editors and authors. He is both a distinguished professor in the UC Davis Department of Plant Sciences and UC Cooperative Extension specialist in consumer quality and postharvest technology in UC Agriculture and Natural Resources.
Chapters also cover rootstock, cultivars, water management, fertilization, fruit growth and thinning, testing for maturity, and supply chain management after harvest. Several more chapters cover pests and diseases, maintaining fruit quality, nutritional aspects and canning.
“This book was a pleasure to contribute to, as it includes information from expert colleagues plus exciting new ideas and applications from our recent researchers,” said Gradziel, a UC Davis professor and plant breeder.
In California, farmers cultivated 36,800 acres of peaches, producing 505,000 tons of fruit worth more than $378 million in 2021. While the crop ranks 23rd in the state, based on cash receipts, California is the No. 1 producer of peaches for the entire United States, according to the California Department of Food and Agriculture.
Crisosto teamed up with colleagues George Manganaris in Cyprus and Guglielmo Costa in Italy to edit this volume, which takes an international look at a growing industry.
Fun fact mentioned in Peach: Nectarines are a peach without the fuzz, a genetic variation. “Most people don't know that!” Crisosto said with a laugh.
Peach contains more fun facts: Peaches are a member of the rose family, China is the world's largest producer of the fruit (growing 60% of the global crop), and industry leaders yearn for trees with a flat canopy so the fruit would ripen all at about the same time and could be harvested easily by machine, reducing the pressure of finding people to pick the fruit by hand.
Peach is available as an e-book and in paperback. Both cost $80 each.
To preview and order the e-book chapters, visit bit.ly/PeachBook. Get a 20% discount with the code CCAB20 during online checkout. The 424-page paperback can be ordered at https://bit.ly/PeachPaperback.
The publisher's sales staff for North America and South America are based in Herndon, Virginia, and can be reached at StylusMail@PressWarehouse.com, (703) 661-1581 or (800) 232-0223.
This Peach book complements our previous publication, “Manual on postharvest handling of Mediterranean tree fruits and nuts,” Crisosto said. “These two publications contain state-of-the-art production and postharvest information that support our research and information centers, UC ANR mission and our academic teaching.”
/h3>- Author: Ed Perry
When you remove young fruit from a limb, the remaining fruits benefit from the reduced competition for mineral nutrients, light, water and plant foods produced by the leaves. By thinning early, you also increase shoot and leaf growth. This results in extra leaves that produce more sugars and other materials necessary for sizing the remaining fruits. Thinning also helps prevent limb breakage caused by heavy crops.
You already thin fruit when you prune your trees, since nearly every pruning cut removes some flower buds. In fact, pruning is the only practical way of thinning cherries and nut crops. However, it is still necessary to hand thin stone fruits such as apricots, nectarines, peaches and plums and pome fruits such as apples and Asian pears. Species that rarely need hand thinning are almonds, avocados, bushberries (such as Boysenberries), cherries, citrus, European pears (such as Bartlett), pistachios and persimmons.
How much to thin depends upon the tree species. With peaches and nectarines, it's important to make room on the branches for each fruit to grow to 2-1/2 to 3 inches in diameter. Thin by pulling off 3/4 to 1-inch long fruit in April and May, leaving one fruit every 6 inches. This results in more fruit on the ground than on the tree, but it's important to produce large, flavorful fruit and to minimize limb breakage.
While it's best to thin early in the season, it is never too late to do some thinning where trees are having difficulty sizing the crop. Removing small fruit from overloaded trees, even shortly before harvest, will pay off in larger average fruit sizes.
Grape varieties such as Thompson seedless may also benefit from fruit thinning. Removing entire clusters after the berries have set helps to enlarge the berries on the remaining clusters. Remove undersized or misshapen clusters first.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
The adult beetles are small (1/8 inch), slender, black beetles with dull yellow wing bands. The larvae are white, short-legged grubs. They are especially attracted to overripe, broken, fermenting, and dried fruits, and are common in orchards, drying sheds, and on fruit trays. The adults lay their eggs on ripe and rotting fruits of all types. They may also infest grapes before they have been completely dried and made into raisins. Fig varieties that have large "eyes" (openings at the blossom ends of fruits) are most affected; fig varieties such as 'Mission' and 'Tina' have small eyes, and are less infested by the beetles.
A complete life cycle of the dried fruit beetle may vary from a minimum of 15 days in the summer to several months in the winter. In winter, both adults and larvae survive in decaying cull fruit of any kind. The pupae generally overwinter in the soil.
Sanitation is the best way of controlling dried fruit beetles. Eliminate potential breeding sites by harvesting ripe fruit promptly and picking up fallen fruit as soon as possible. Keep cull fruit in tight garbage cans or garbage bags until disposed of. If you dry fruit, you should thoroughly clean your drying trays after each use.
You may want to try trapping to reduce dried fruit beetle infestations. To do this, place several overripe peaches in a bucket, then coat the insides of the bucket with 90-weight oil, Tanglefoot, or a similar sticky material. Once the buckets are hanging in the tree, the fermenting peaches attract the beetles, and they become trapped in the sticky material. This method will give you partial control only.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
- Author: Ed Perry
If you do not prune your trees enough, they will become too tall to harvest, even with a tall ladder. If you have an unpruned fruit tree in your garden, you know that most of the fruit grows in the top. Yearly pruning is necessary to keep the tree at a reasonable height, for instance, no more than 10 or 12 feet high. If your tree is already overgrown, you may want to reduce its height gradually, say over a two-year period.
The main objectives of pruning mature fruit trees are to reduce the number and increase the size of the potential crop, to develop new fruit wood, to remove interfering and broken branches, and to contain tree height and spread for convenient harvest. Most fruit trees, when not pruned, produce more fruit than they can size and mature properly. You can prevent such overproduction with yearly pruning.
Persimmons, many figs, quinces and pomegranates bear fruit on current season's growth. When you prune these trees, remove old and weak branches, leaving some younger branches to produce new growth and fruit the coming year. Overcrowding and lack of sunlight will cause branches to die, so you need to thin out some branches to allow light infiltration into the tree so that the fruit wood stays healthy.
Nut trees such as almonds and walnuts do not need as much pruning for height control as fruit trees. You harvest nuts by knocking them down with a long pole, rather than by hand picking, so the trees can be much taller.
Fruit Tree Resources
Fruit Trees: Training and Pruning UC ANR Publication
The California Backyard Orchard For more details about training and pruning deciduous fruit trees.
Citrus and Avocado Trees Require Little Pruning For information on pruning citrus and avocado trees.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
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