Predators and other natural enemies need help to maintain and improve codling moth control programs.
Once-stable integrated pest management programs for apples, walnuts and pears in Western orchards began to show cracks as organophosphates fell out of favor.
The softer, more targeted products replacing them seem to affect orchard systems in less-clear ways, including outbreaks of previously controlled secondary pests, such as spider mites, aphids and pear psylla, says Vince Jones, entomology professor at Washington State University’s Wenatchee Tree Fruit Research and Extension Center.
Jones serves as director of a three-state team studying ways to improve codling moth programs through enhanced biological control.
“Secondary pests are easily managed by natural enemies—as long as we don’t disrupt the natural enemy cycle,” says Nick Mills, professor of entomology at the University of California, Berkeley.
While new pesticides may be less toxic to humans, “that doesn’t mean they’re low risk to natural enemies,” Mills says.
Subtle, longer-term effects
Standard pesticide studies look at outright mortality in non-target organisms, but may not catch more subtle, longer-term effects, Jones says.
Parasitic insects, spiders, ladybird beetles and other natural enemies may be suffering from long-term population reduction through pesticide-induced sterility, lower egg production or changes in sex ratios, Jones says. Pesticides also may draw out the kill time for some beneficials beyond studies’ 24- and 48-hour exposure windows.
“It’s not as bad as killing them outright,” says Peter Shearer, entomology professor and superintendent of Oregon State University’s Mid-Columbia research center in Hood River. “But if they’re not there in numbers to provide control, then they can’t get the IPM job done.”