Leafroller larvae form webs and use them to curl leaves into protective structures.

Leafroller larvae form webs and use them to curl leaves into protective structures.

Photo Courtesy Of Washington State University

Obliquebanded leafroller has been increasing as a problem in tart cherries in recent years, where the black-headed green larvae are a highly undesirable contaminant at harvest time in July.

Entomologist Dr. Nikki Rothwell, coordinator of the Northwest Michigan Horticultural Research Station northwest of Traverse City, said the insect is not a fruit feeder on tart cherries as it is on apples. But the larvae, rolled as they are into leaves on the trees, get shaken loose when trunk shakers harvest the cherries. They fall onto the collecting frames and are conveyed with the fruit into the tanks of water that growers use to transport the fruit to cooling pads and then can potentially be shipped to the processing plant for canning, freezing, or drying.

Under U.S. Food and Drug Administration rules, there is zero tolerance for insect parts or larvae in tart cherry products, and growers have fought plum curculio, cherry fruit flies, and other insects that inhabit cherries with their larvae.

Obliquebanded leafroller, while it doesn’t feed on or in the cherry fruit, is emerging as a contamination issue, Rothwell said, particularly as the insect is increasingly resistant to organophosphate insecticides. In studies conducted back in 2000, Michigan State University entomologists Dr. John Wise and Dr. Larry Gut found that  it took considerably higher rates of of azinphos-methyl to kill leafrollers—and they are likely cross-resistant with pyrethroids and other different insecticide classes.

Tart cherry growers will lose azinphos-methyl as a tool after next year, so most are now shifting to the new, reduced-risk insecticides like Delegate, Altacor, and Belt. These new lepidopteran materials work well on leafroller larvae, but growers should be cautioned that larger larvae are harder to kill than small ones.

Larvae, she said, form webs and use them to roll leaves into protective structures, from which they move in and out to feed. Adults overwinter in the bark of trees, emerging in June and July to feed on buds and leaves, and lay eggs. Cherries are harvested in that time frame.

Rothwell recommends growers use traps to monitor for the presence of adults and spray when larvae are small, before they roll themselves into leaves. Growers need to choose a material they can apply preharvest and eliminate the larvae by harvest time.

“We do not recommend the use of OPs for OBLR control any more,” she said, noting the likely growing resistance of leafrollers to organophosphates. “Control them early when larvae are small. Consider using the newer insecticides that have short preharvest intervals and will knock down the larvae. Some of these new materials need to be ingested to work.”