Published on Wednesday, 30 November -0001 00:00
Apple trees are not even in bloom yet, but judging from the number of inquiries I've received recently, homeowners are definitely concerned about controlling apple pests this year. This does not surprise me because 2008 could be called the "year of the apple maggot" as I saw more heavily infested apples than at any other time in my career. A number of the people that brought apple samples to my office had applied an insecticide to their trees, but had poor pest control because they did not apply the chemical at the proper time. There are three insect pests that may infest apples in this area: the plum curculio, the codling moth and the apple maggot. All of these pests can be controlled with a spray program or an alternative method and sanitation, but timing is critical. Plum curculios overwinter as adult weevils in plant debris on the ground. They move to apple and stone fruit trees to lay eggs about the time the trees bloom. As the female weevils lay their eggs, they create crescent shaped scars on the apple skin. Severely attacked apples become deformed and knotty-looking and often fall from the tree. Larvae feed for about two weeks after which they exit from fallen apples and pupate in the soil. There is one generation a year. Protect apples and stone fruits from the curculio by making two chemical applications, one when about 3/4 of the petals have fallen and a second application ten days later. Use a registered insecticide like malathion, or a complete fruit spray that does not contain carbaryl (Sevin). Avoid the use of carbaryl at this time because it is deadly to bees which are still active. If used within 30 days after full bloom, it can also cause fruit drop. Codling moths overwinter as mature larvae and the moths start to appear in spring as the last petals fall from apple blossoms. Female moths lay eggs on developing fruit or on nearby leaves. Coddling moths damage apples by burrowing through the apple into the core, either from the side of the apple or from the calyx end. They also cause stings where the small larvae begin to feed and then stop. Because they are active at the same time, the spray program for plum curculio also controls the codling moth. Apple maggots, also known as the railroad worm, are the most destructive pests of apples grown in home orchards. The apple maggots spend the winter in the soil as pupae and begin to emerge from the soil as adult flies in July. These flies do not all appear at the same time, but continue to emerge until September, making it important to apply some type of control until harvest. Shortly after emergence, the female flies begin to lay eggs in the developing apples. These eggs hatch into cream-colored, legless maggots that feed and tunnel in the flesh of the apple. Apple maggots cause two types of injury. The first type of damage occurs around the site where the skin of the apple is pierced during the egg-laying process. The flesh of the apple stops growing at this site where the skin was pierced, resulting in a sunken, misshapen, dimpled area. The second injury occurs as the maggots tunnel through the flesh. As a result, the pulp of the apple breaks down, discolors and starts to rot. If applied before the flies are able to lay eggs, insecticides help prevent apple maggot damage. The insecticide sprays need to thoroughly cover all surfaces of the leaves and fruit to be effective. Once the female flies have laid their eggs, there is no effective management. Carbaryl (Sevin) or esfenvalerate (Ortho Bug-B-Gon Max and others) are effective chemicals labeled for apple maggot control that are readily available. The most effective method of application is to apply the insecticide every 10-14 days beginning July 1, making at least 3 applications. Be sure to note the interval between the last spray and when you can safely harvest the apples. Do not pick the apples sooner than the time indicated on the label. Always read pesticide labels carefully before buying and again before using these products. The label is the final authority on how you may legally use any pesticide. An alternative to insecticides is management of apple maggots by trapping the adult flies with sticky red sphere traps. You can purchase these traps in some garden stores or order through mail-order catalogs. You can also make your own traps by using a plastic or wooden ball about three inches in diameter, colored red or black. Attach a wire to the ball and coat it with a sticky substance such as Tangle-Trap. You can also purchase a pheromone attractant to make the sticky traps more appealing to the apple maggot flies. Hang one trap for every 100 apples which amounts to about five traps for an average standard tree. The traps should be in place by the last week in June. If the traps become covered with insects or debris, clean them and reapply the Tangle-Trap. Removing the sticky substance can be challenging to some people, but if the balls are covered with a small plastic bag or plastic cling wrap before applying the Tangle-Trap, clean up is as easy as removing the plastic. There are "recipes" for mixtures of sugar, vinegar and water that can be placed in containers in the trees to attract the apple maggot flies. Although these mixtures do attract and kill some of the apple maggot flies, they also attract and kill many beneficial insects and are, therefore, of questionable value. Sanitation is very important in reducing apple maggot numbers. When infested apples fall to the ground, the maggots exit the fruit and burrow several inches into the soil to pupate. Therefore, it is important to dispose of apples as soon as they have fallen to the ground to reduce the number of overwintering pupae in your orchard. Feed the apples to livestock or bury them at least one foot deep. Do not place them in your compost bin. For an excellent up-to-date online publication that covers the key insect pests and diseases of apples and both chemical and non-chemical control measures, go to and search for "Integrated Pest Management for Home Apple Growers."