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Will winter freeze cut pest trouble? Opinions vary

Issue Date: January 15, 2014
By Kate Campbell

Cold, dry conditions may carry some benefits for farmers worried about producing a crop this year—but those looking for any silver lining in 2014 could find the gleam they see is tinfoil. Experts say the upcoming growing season will be challenging for all crops, but years that follow cold, dry winters often have lighter pest pressure.

Most pest experts cautiously agree freezing temperatures and lack of rain translate into fewer pests migrating into commercial crops in spring and summer—and that usually translates into a reduced need to apply crop-protection materials.

"We all hope there's a benefit from the winter freeze events in terms of pest suppression," said Scott Hudson, San Joaquin County agricultural commissioner. "Usually, a warm winter results in more pest pressure the following summer because a lot of adult insects don't die off.

"We can hope the cold weather reduces populations, but bugs are pretty resilient," he said, noting San Joaquin County crops survived more than a week of sub-freezing temperatures without reports of widespread damage.

"Based on my experience, when there are no host plants, pests can't overwinter and that leads to lighter pest pressure during the following growing season," Fresno County farmer Marvin Meyers said. "I expect we won't have as much trouble with navel orangeworms, but mite populations may explode in hot, dry conditions."

Well-cleaned almond orchards probably will fare pretty well, he said, "and I don't think we're going to have trouble with stinkbugs because there are absolutely no host plants around for them to overwinter. Everything is dry."

In citrus crops, where infestations of Asian citrus psyllid continue to turn up, Mark Hoddle, University of California, Riverside, entomologist, said, "Cold temps always have an impact on citrus pests, diseases and insects. The question is: How cold and for how long does it need to be for the effect to be really detrimental to the pest?"

For citrus, if temperatures don't drop cold enough to damage trees or kill them, then it's possible the psyllid and huanglongbing, the tree-killing virus the pest can carry, may survive, too.

"We don't understand how cold affects ACP," Hoddle said. "In Punjab, Pakistan, the winter temps are very similar to the Central Valley, and ACP and HLB have survived there for a very long time. Where trees are protected from cold, and if ACP and HLB are also protected on those trees, then they will likely survive, too."

Ventura County has been under quarantine because of psyllid infestations for several years. However, cold temperatures this winter do not appear to have slowed the insect's spread.

In December, the California Department of Food and Agriculture confirmed two psyllids were found in a backyard tangerine tree in Ojai—next to a commercial orchard in an area known for its tangerine production. This area of small, specialty farms had previously been free of the pest. Treatments are now underway.

Tulare County Agricultural Commissioner Marilyn Kinoshita said last week the early December freeze did not appear to have reduced psyllid populations in Tulare County, which is under quarantine for the pest.

More infestations turned up within quarantine boundaries and the pest was found in traps near juice plants that use citrus supplies from coastal and desert growing regions.

Elsewhere in the San Joaquin Valley, experts noted two types of farming activities—permanent plantings of trees and vines, and annual crops. Pests can survive year-to-year in permanent plantings, but with annual crops, pests must move into the crops from surrounding vegetation.

"I've been doing a lot of work on lygus and working on ways to predict whether it's going to be a severe pest year for the cotton crop," said Peter Goodell, UC Cooperative Extension advisor in Parlier. "It's not tight science, but pest pressure tends to be related to rainfall patterns. After 35 years of working with crops, my experience tells me a good water year is a bad bug year."

Last year was a heavy pest year in the valley, Goodell said, with aphid outbreaks in alfalfa and leafhoppers in tomatoes—followed by curlytop virus—plus stinkbug and lygus problems.

Pest experts on the Central Coast are of the same opinion. UC Cooperative Extension entomologist Shimat Villanassery Joseph said the upcoming crop year will see variations in pest pressure, depending on crop type and irrigation practices.

"We had a problem with invasive bagrada bugs in the southern Salinas Valley last summer," Joseph said. "We were finding very high population levels, but when it got colder, numbers went down substantially. I'm estimating that 50 percent of the population or more died. But, they are still around. These bugs have the ability to withstand cold."

Joseph said it's hard to generalize given all the environmental variables, but in general he expects farmers will find lighter pest pressure from some of the most troublesome crop pests found on the Central Coast.

(Kate Campbell is an assistant editor of Ag Alert. She may be contacted at

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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