Apple maggots must be controlled

Apple maggots are a fairly new, but serious pest of apples in the Northwest. They were first detected in Portland in 1979 and have since spread to all the counties in Western Washington and to Spokane, Kittitas, Klickitat and Yakima counties on the East Side. Their presence in commercial orchards can have serious impact on an important element of the state’s economy. Because of this, homegrown fruit technically can’t be moved out of the area.

The maggots are creamy-white worms about a quarter of an inch long that tunnel through the flesh of the fruit. They are the larvae of the apple maggot fruit fly; a housefly-sized insect with a black body, large dark red eyes, a black and creamy-white abdomen with a distinctive white spot. The transparent wings are banded with black.

The adults emerge from the ground in late June and are active until October. They lay single eggs under the skin of the fruit and will lay about 300 eggs in a 30-day period. The eggs hatch in three to seven days and begin tunneling through the fruit. The fruit subsequently rots and falls from the tree. The larvae then burrow into the soil to pupate over the winter. Each fly has only one generation a year. The apple maggot is only open to control at the adult stage. Once the eggs are laid in the fruit, they and the larvae are out of reach of any control method.

The flies are detected by using yellow or red sticky traps baited with an attractant. The yellow traps are flat and resemble apple leaves while the red traps are round to mimic apples. They are hung at head height among the foliage and fruit so the flies can see them. Traps should be hung by early June using one for small trees and up to three for large trees. Once the insects are detected, a control program needs to be started immediately.

There are no biological or organic controls readily available to the home grower. Traps can be used to catch adults but aren’t going to get them all. All fallen apples must to be picked up to keep larvae from crawling from the apple into the soil. Damaged apples should be discarded and not composted. Seemingly undamaged fruit needs to be monitored as eggs continue to hatch. The best way to control the fly may be to remove the tree completely if you aren’t using the fruit.

For conventional home growers, Malathion needs to be applied at about 10-day intervals through the rest of the apple season.

A specially processed nontoxic kaolin clay (Surround at Home) can sprayed on the fruit and trees. The clay covers the tree with a white powder that camouflages them to the fly. It is easily washed off but does leave the tree looking a bit ghostly. It may be hard to find locally.