Pear growers face greater difficulty with psylla, he says. Some products used against codling moth are toxic to psylla’s natural enemies, while early-season sprays of low-dose pyrethroids can build to dangerous levels over time.
Managing psylla through biological control would produce substantial reductions in spray costs, Shearer says.
Pesticides’ effects on natural enemies
Mills’ assignments revolve around walnuts, starting with lab tests of recently released pesticides along with those still in the pipeline. “We’re getting the start of an idea of which ones are likely to be most disruptive to natural enemies,” he says.
Rimon (novaluron) and Delegate (spinetoram), for example, seem to pose problems in the lab for natural enemies. Field tests starting later this year will attempt to confirm those results under commercial growing conditions.
Parasitic wasps that have reined in walnut aphids since the 1970s now seem to suffer disruptions from some of the new products.
Along with looking at sublethal effects on natural enemies, Jones and his team hope to develop better phenology models for natural enemies and spray strategies that minimize impacts on beneficials without sacrificing pest control effectiveness.
New monitoring techniques
That requires new ways to monitor target species, including finding the best attractants for lures. These new methods also will be “valuable additions to the toolbox” for growers and pest-control consultants, Mills says.
And because the natural enemies involved typically are found in many different crops, developments here could aid more than just tree-fruit growers.
But predators aren’t easy to study. “Unless you actually catch them in the act of eating something, it’s hard to say which is responsible for what,” Jones says.
Tom Unruh, research entomologist at the U.S. Agriculture Department’s Agricultural Research Service unit in Wapato, Wash., is trying to solve that problem with a two-pronged approach: orchard video cameras and gut-content analysis.
Producing sufficient solid data from the cameras has proved tricky, Unruh says, but he’s logged some surprising initial results.
“So far we’re seeing birds and rodents doing most of the work” when it comes to predation of codling moth larvae, he says.
The cameras also clarify the importance of the predatory ground beetles that orchard folklore holds up as a key codling moth predator. While the beetles zero in on moving larvae, they ignore the cocooned form in which the moth spends six months of its life, he says.