Viewpoint: Cherry fruit fly appears on local crops

by Margaret Cooper This month people have started reporting that they have found grubs in their cherries. While we do not have an official identification yet, apparently the cherry fruit fly has arrived in Powell River.

The fly is species-specific and attacks only cherries, both sweet and sour. It is well-known in the cherry-growing regions of the Pacific Northwest, and unfortunately, it is a very bad pest.

The adult is a small striped fly with striped wings, about half the size of a house fly. It pierces the skin of ripening and ripe cherries to lay its eggs. The lava hatch as small white maggots that eat the inside of the cherry for about two to three weeks before boring an exit hole and dropping to the ground to pupate over the winter until next spring.

We have reports of infested trees from Wildwood and Cranberry. Central Westview reports are clear so far except for one case of the grub reported in Grief Point. In all cases, fruit picked from the tree early in the season was clear, with grubs being noticed only around July 20.

There are a few things that residents can do to help mitigate the spread of this fly.

• It is very important that everyone with a cherry tree clean up as much of the fallen fruit as possible as well as old fruit still on the tree. Do this whether cherries have been infested or are still clear. The adult fly can travel up to half a kilometre searching for cherries in which to lay its eggs. Wild trees left in abandoned gardens, uncared for, are an ideal spot for the incubation of the fruit fly.
• Put the cherry debris in a black plastic bag in the sun and let the grubs bake. For people who have chickens, allow the chickens to scratch and feed under the cherry trees. Otherwise, spread mulch or ground cover under the trees to prevent the pupa from being able to burrow into the soil.
• Do not give away infected fruit. For anyone receiving infected fruit, boil it up before discarding. Be very careful about moving cherries around the area. Transportation is by far the worst way for spreading disease and pests.

The important time to try to kill the fruit fly is going to be next May and June when the flies hatch and are getting ready to lay their eggs. Powell River Garden Club and the Master Gardeners will circulate further advice on this in plenty of time next season.

I am trying to map the occurrence of the cherry fruit fly so we can get a good plan of attack. If anyone has a cherry tree, or knows about a neighbouring tree, please let me know where the address and whether the fruit is clear or infested. Readers can contact me at 604.485.2143 or [email protected].

Margaret Cooper is a resident of Powell River and current president of Powell River Garden Club.