Also known as apple fruit fly, the adult apple maggot fly is similar to the house fly and lays eggs inside the flesh of the apples around late July. They usually go unnoticed until you bite into an apple. The larvae overwinter in dropped fruit, so discarding and cleaning up fruit from the ground in the fall is a good idea.
You can make a trap to catch the flies before they lay their eggs. Mix one part molasses to nine parts water and add some yeast to encourage fermentation. Pour the beer-smelling liquid into small, plastic containers. Once fermentation subsides, hang the containers from your apple trees.
Another remedy; The Cooperative Extension of New Hampshire uses a bait made of 2 tsp ammonia and 1/4 tsp soap powder mixed in a quart of water. Distribute to smaller containers and hang them on the sunny side of the trees. Renew the bait if necessary.
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