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Check the tree and the ground under it. In late June, the process called "June drop" naturally thins out the clusters of fruit. The tree sheds excess small fruits, leaving a few to receive nutrients and ripen fully. Rake up fallen fruit, whatever its size. Getting rid of all old plant parts is a basic part of fruit tree disease and insect management. Also, if the area under the tree is cleared, you'll be able to watch for additional fruit falls that will indicate possible insect infestations.
Don't compost any fruit that's insect-infested or diseased. Add it to "clean green" pickup or put it in the trash pickup. Clearing grasses and weeds from under fruit trees can help with sanitation, since it's easier to rake and tidy where the ground is bare. Most fruit trees grow better if an area of cleared, open ground surrounds them. Mulching under the tree will help deter annual weeds and retain soil moisture.
In particular, learn to identify apple maggot (Rhagoletis pomenella) and the damage it does. A pest in western Washington since about 1979, the apple maggot has gradually spread through westside counties. It has been found in most western Washington counties.
Reducing the spread of apple maggot in home gardens will help protect commercial apple orchards in western Washington. The Skagit Valley, for instance, now has acres of Jonagold and other apples, acreage representing large economic investment in a crop that would be severely damaged if infested by apple maggot. Apples affected by apple maggot damage are completely useless. They can't be sold and they disintegrate from decay so that they can't be used for home consumption.
The Washington State Department of Agriculture has been surveying populations and working to keep the public informed about the problem for more than 20 years. Roadside signs placed along highways in western Washington say "Apple Maggot Quarantine area/ Please do not transport home-grown tree fruit." These signs have been in place so long that they are probably not noticed by most drivers, or if noticed are not understood. The infestation can be carried from one area to another within fruit, because the apple maggot grows to maturity inside an apple.
The apple maggot is the juvenile stage of a fly. The adult fly emerges during early summer, mates, and lays eggs. The adult fly is black and white, about ¼ to 3/8 inch long. It doesn't look like a common housefly because it has distinct black and white striped markings on the wings. Adults will be hatched and flying now. Cool weather delayed the emergence, but monitoring in south Seattle detected a few adult flies in mid-June.
The fly pierces the apple skin to lay eggs underneath. The younger the apple, the less likely the egg will survive and hatch. As the summer advances, the ripening flesh of the apples provides good habitat. From mid-July on, the larger and softer apples increase the survival rate of the pest and the chance of spreading the infestation. The egg hatches into a maggot that chews its way into the ripening apple to dine while growing. The entry hole for an apple maggot resembles a pinhole. The space around the entry hole is clean. But the inside of the developing apple carries messy trails that show the maggot's progress throughout the flesh. As it eats, the maggot leaves a trail of rotting apple flesh where it has passed. In the eastern United States, where apple maggot has been a problem for decades, it was nicknamed "railroad worm" for the tracks intersecting within the apple.
After feeding inside the apple, the apple maggot leaves the apple to pupate in the soil around the tree. Most maggots stay in the apple until it falls, making the journey from the apple to soil quite convenient. Obviously, if a grower tossed an infested apple out a car window, the maggot could land on soil and grow to adult stage, thus moving the infection to another region.
If you think you may have codling moth damage rather than apple maggot damage, look at both the entrance hole and the interior of the apple. Codling moth larvae, the juveniles of a moth, leave distinctly different signs than those of the apple maggot. The entry hole is surrounded by a pile of brown "frass," (digestive by-products). The codling moth larva bores to the center of the apple and dines on the protein-rich seeds. Codling moth infested apples can't be sold, but much of the apple flesh is unaffected and can be peeled away and used for cooking. Don't put the infested pieces into compost piles.
Control and management of apple maggot includes several steps.
http://gardening.wsu.edu/library/tree006/tree006.htm
Joining the Western Cascade Tree Fruit Society will get you lots more information from local amateur growers. Sources for traps and bags and directions for banding are included in their meetings. The society members produce two newsletters: The Bee Line, and The Urban Scion Post from the Seattle Tree Fruit Society.To join, write to The Seattle Tree Fruit Society, 2625 13th Avenue West, Unit 306. Seattle, WA 98119. enclosing $18 for annual membership in both the Western Cascade Tree Fruit Society and the Seattle Tree Fruit Society.
Apple Maggot Pesticide Recommendations
Hortsense: Managing plant problems with Integrated Pest Management
