Get Wise To Apple Maggots, Other Nasty Fruit-Tree Pests

After a cold, wet spring, fruit gardeners eagerly look forward to seeing little green apples turn into juicy, edible treats. In early June, two major insect pests begin to infest and damage maturing fruit. Now's the time to check the insect activity on backyard apple trees, looking for evidence of codling moth and apple maggot.

Fruit-tree management is a year-round project. Experienced apple growers know that the winter cycles of pruning, using dormant sprays and cleaning up around trees are vital to good crops. But these tasks don't complete the care needed for fruit trees. Planned actions over the entire growing season must happen.

It's important to know about keeping a "clean" garden, especially for those new to fruit growing. Tidy around the growing area thoroughly, raking and disposing of fallen fruit or leaves throughout the year. Windfall fruit, even unripe fruit, can attract large vermin like rats, squirrels, raccoons and possums. It also offers sanctuary to overwintering stages of insects that can emerge and harm the crop. Encourage neighbors to remove fallen fruit.

Birds living in the garden also help out; chickadees, nuthatches, and other birds eat insect pests. Chickadees even clean aphid eggs off the bark of trees during winter. Minimize all pesticide use to help encourage birds. Always provide a source of clean water for birds, especially in summer when rain is scarce. (It may seem that rain will never be scarce during 1996, but we're headed into the generally dry season.)

Apple maggots, a serious pest, are found in most counties throughout Western Washington, and have been increasing since about 1979. The name is familiar to travelers from signs on major highways stating "Apple Maggot Quarantine Area: Do not Transport Home-grown Fruit." Apple maggots, the larval stage of a fly named Rhagoletis pomenella, tunnel through apples and leave areas of decayed pulp - no part of the affected apple can be used. Tossing an apple out a window can also distribute the pest insect, hiding in the fruit. Surveying and monitoring exists to protect the commercial-orchard industry.

These pests can attack crab apple and ornamental hawthorn as well as apple. Commercial growers remove hawthorn from areas around orchards as part of efforts to control apple maggot. It's also good practice to remove "feral" untended old fruit trees near home orchards, if possible.

Orchardists suggest setting traps to check for apple-maggot presence from June 1 to harvest time, replacing trap coatings every two weeks. A wood-panel trap, coated with attractant and a sticky tanglefoot goo, is easy to build. Commercial apple-maggot traps, red balls with attractant, are also available. Properly placed traps will catch some of the adults before they lay eggs under the skin of maturing apples. The adult flies are about one-quarter inch long, distinctly marked in black and white. For specific directions on building an apple-maggot trap, consult the April 1996 issue of the "Urban Scion Post" newsletter of the Seattle Tree Fruit Society. (Write STFS, 4916 52nd Ave. S., Seattle, WA 98118 and enclose a self-addressed stamped envelope.) One grower in Southwest Washington trapped 278 apple maggot flies from just a few dwarf apple trees. Traps help!

When eggs are laid on growing apples, the larva spends about 30 days inside the fruit, reducing it to mush in the process of eating and growing. They exit and spend the winter in a pupal state (non-feeding), just below the ground surface. Clean up and destroy all fallen fruit to keep larvae from overwintering. If chemical control is necessary, follow the spray schedule in WSU Extension Bulletin 0846, "Disease and Insect Spray Schedule: Apples and Pears."

Monitoring, trapping and keeping a clean garden can allow a few sprays to work effectively, rather than making the use of many sprays necessary. Call WSU Cooperative Extension to order bulletins, in Seattle at 296-3900; in Tacoma, (206) 591-7170. There is a cost for bulletins and handling.

Codling moth, Cydia pomonella, is probably the most universally damaging apple pest in Western Washington. It can also attack pear and fruiting quince. Larvae hatch out from eggs laid about the time apples blossom, emerging in six to seven weeks to infest the ripening fruit.

The moth larvae enter the fruit, often at the calyx end, and feed on apple pulp and seeds in the center of the apple. Damage will be concentrated around the apple core and entry hole. Piles of frass (insect dung) may show around entry hole.

Damaged apples can used for for cider, or trimmed for cooking, but they are not sellable. Clean up all fallen apples from June 1 to the last apple of autumn. Destroy apple parings and cores containing codling moth larvae. (Place in sealed bag in the trash, do not compost.) Organic apple growers set out traps in early April, with a mix of one gallon water, two cups apple cider vinegar and one teaspoon yeast. Set pheromone traps in May and June, high in the trees, to trap adults.

In mid-July and later, larvae will be coming out of apples and moving down the tree to find sites for cocooning. They can be caught in a folded band of burlap wrapped around the tree trunk and secured with clothespins. Fold the band over to make several layers and place it so that one fold at the bottom makes escape from the trap impossible. Shake the larvae out into a bucket of soapy water. Keep bands tended until the end of harvest. Careful fruit-tree management means keeping a clean garden and using traps wisely. Apples can be great garden crops, but untended apple trees lead to insect infestations. To emphasize the garden principles of the Green Gardening Program, the Practical Gardener features articles on reducing pesticide use in the garden. To see these techniques in action, attend the 1996 Green Gardening Program Tour, June 29 and 30. For information or to receive a tour map, call 547-7561. The Green Gardening Program is presented by the combined efforts of Seattle Tilth, the Washington Toxics Coalition and WSU Cooperative Extension, King County. It is sponsored by the Seattle Solid Waste Utility and funded by the Local Hazardous Waste Management Program in King County.