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Control cherry fruit fly after harvest

Flies developing from eggs laid around harvest will emerge in future years.

Michigan tart cherry growers are being advised to apply one more insecticide spray—after harvest is over.

The reason is, cherry fruit flies are using the small amount of fruit left on the trees after they’re shaken during harvest to maintain their populations and be there for the crop the next year.

“We’re finding much of the cherry fruit fly activity is taking place after harvest,” said Dr. Larry Gut, Michigan State University extension entomologist. One insecticidal spray, within seven days after harvest, using a material such as Provado (imidacloprid), can clean up the orchard and reduce fruit fly pressure the next season.

Tart cherry growers are finding they need to do more spraying after harvest than they once did. They need to keep healthy leaves on the trees longer to assure good tree health and fruit quality in future years, so they now spray more times postharvest with fungicides to reduce the effects of cherry leaf spot. Now insecticides should join the tank mix. “Add it to your post-harvest spray for cherry leaf spot,” he said.

Gut and his team of entomologists have studied cherry fruit fly for several years and found that there are several distinct populations, being selected for naturally by fruit ripening time and genetically by the spray programs growers use.

Cherry fruit flies that infect the later-maturing wild black cherries are not an issue for growers, Gut said. Growers had suspected that wild hosts were providing a source of pest pressure, but Gut found that not to be the case. The flies that infest wild cherries are a separate population that mate and lay eggs later in the summer after tart cherries are harvested and gone from the orchards.

The introduction of new reduced-risk insecticides and the move away from azinphos methyl has altered the selection pressure because the new materials are not as residual, Gut said. This has resulted in a shift in cherry fruit fly population toward those that emerge three to four weeks earlier.

To avoid residues, growers need to quit spraying as harvest nears. “You want residues to be gone at harvest, but you need to come back immediately after harvest and spray if your traps show cherry fruit flies,” he said.

When trees are shaken for harvest, some remain on the trees—especially high up on more willowy wood. That’s exactly where cherry fruit flies like to be, Gut said. In years of excess supply of tart cherries—and last year was such a year—some growers leave fruit unharvested to reduce supply under the federal market order governing tart cherries.

“Diverted cherries—any cherries left in the orchard on the trees—provide a potential food source,” Gut said. The most important cherry fruit flies to control are those laying eggs near or soon after harvest, as they will be the ones that emerge at harvest time in future years, he said.