The most serious pest of apples in Connecticut is the apple maggot or, as it is sometimes called, the railroad worm. This insect is responsible for the brown, rotten streaks found in fruit that otherwise look sound and pest free at harvest. In neglected or poorly sprayed orchards, 100 percent of the fruit can be wormy. Infested fruit has a tendency to drop prematurely.
Apple varieties most susceptible to maggot attack are Wealthy, Cortland, Gravenstein, Red and Golden Delicious and early sweet or subacid varieties. However, the maggot will attack any variety. The fruit of early ripening varieties and of severely infested late ripening varieties are usually quite distorted.
The adult apple maggot is a two-winged fly slightly smaller than the common housefly, about 1/5 of an inch. It is black except for white bands on the abdomen, three on the male and four on the female, and a white spot on the upper surface of the body near the point where the wings attach. The wings are transparent with conspicuous black markings. The maggots themselves are small, white, peg-shaped, legless larvae or worms.
Source of Infestations
Apple maggot flies migrate into previously un-infested trees from unsprayed or abandoned apple trees somewhere in the vicinity. They are known to migrate for at least half a mile. Once the flies have become established, sprays for their control may be needed for a few years.
Causes of Infestations
Infested fruit in orchards is usually the result of insufficient spraying. The flies appear in late June. They usually remain active at least into September and often much later. Many home orchardists tend either to stop spraying or spray at less frequent intervals during this period, since the damage to the fruit is not obvious.
The apple maggot passes the winter in a pupal stage in a brown oblong case about a quarter-inch long known as a puparium. These puparia can be within two inches of the soil surface. Adult flies begin emerging from the puparia late in June and continue to emerge through September and sometimes as late as early October. The flies mate, and the females begin to lay their eggs singly in tiny punctures that appear as pinpricks made in the skin of the apple. The eggs hatch, and the larvae begin to tunnel through the flesh of the fruit, leaving tarnished, irregular threadlike trails. When full grown, about 1/4 inch long, the maggot leaves the apple, usually after they drop, and enters the ground to pupate. Maggots spend the winter in the puparia until the following summer. However, it is not unusual for them to spend one to two years in the soils before emerging as mature flies.
Some control can be achieved by picking up and destroying dropped apples before the maggot leaves to enter the grass. Emergence of the flies can be monitored by using red sticky spheres or yellow baited traps. The red balls can be made by painting 2 to 3-inch balls red or using commercially available plastic or wood balls. (They are also available at many IPM websites.) These are covered with a petroleum jelly or a commercial sticky trap such as Tangle Trap. Only one or two traps are required if they are used for monitoring. Spray with the appropriate insecticide when an average of 5 flies are captured. Apple maggot fly captures made the first week after spraying are discounted because it is assumed they would have died if they had landed on protected fruit. Monitoring is continued after the seven-day period provided no more than one inch of rain fell.
To control apple maggot flies with sticky traps, use one trap per full dwarf tree (under eight feet) two to four for a semi-dwarf and six to eight for a standard tree. Clean the traps weekly of large insects and recoat every three to four weeks. Use of an apple volatile lure is said to increase the effectiveness of the trap.
The apple maggot can be controlled with general-purpose fruit spray mixtures available under a variety of brand names at most garden supply shops and hardware stores. However, applying an insecticide easy on predators and other beneficial insects would be better. For insecticide options, contact your local Cooperative Extension center.
Timing of Sprays
Control measures should start a few days after the flies emerge (about July 1) and continue at intervals not exceeding 10 days, as long as flies are active. During peaks of emergence, usually the latter part of July, spray intervals may need to be shortened to seven days, depending on number of flies captured on traps. Any treatments missed during the period of maggot activity can result in wormy fruit.
Most damage to fruit is usually caused by late-emerging maggots. Activity usually ceases in late August or early September, but can last into October. If spraying is stopped more than two weeks before harvest, expect some trouble from maggots.
Updated by: Mary Concklin, UConn IPM. 2012
Revised by: Edmond L. Marrotte, Extension Consumer Horticulturist, Department of Plant Science
Originally written by: Milton G. Savos, Extension Entomologist Emeritus
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