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Apple Maggot

The adult apple maggot, Rhagoletis pomonella, AKA  "railroad fly," is a black-bodied fly that is slightly smaller than a housefly. The abdomen of the fly displays white bands (three on the female and four on the male) and the clear wings are also crossed by black bands.

Symptoms

Pocked and rotted fruit, maggots in fruit.

Organic Treatments         

The most effective preventative measure against this pest is to clear any fallen fruit from around your trees. This will remove maggots before they enter the soil for winter. If a pesticide is to be used, it must be carefully timed to coincide with the emergence of the adult fly, as this is the only period in its cycle that the insect is vulnerable. Red sticky balls can be hung in apple trees to monitor fly activity. A threshold of 5 flies on a sticky trap means that it is time to spray. Surround, Spinosad and Pyrethrin are all chemicals that can help suppress apple maggot.

Conventional Treatments

Once a threshold of five flies on a sticky trap is reached it is time to spray. Delegate provides suppression and is not restricted in most states. Effective restricted chemical include Assail, Avaunt, and Altacor.

Insect Cycle

The adult apple maggot, Rhagoletis pomonella, AKA  "railroad fly," is a black-bodied fly that is slightly smaller than a housefly. The abdomen of the fly displays white bands (three on the female and four on the male) and the clear wings are also crossed by black bands. From the middle of June through August, these adults emerge from puparia in the ground where they have overwintered. Once they have emerged, the flies must feed, mate, and lay eggs within ten days. To lay her eggs, a female "stings" an apple with her sharp ovipositer and inserts a single tiny white egg into the flesh. She will do this up to 400 times! When the eggs hatches, the maggot begins to burrow through the fruit as it feeds, and the fruit often rots and falls to the ground. The maggot leaves the rotting fruit and digs itself one or two inches into the soil, where it changes into a pupa for the winter. The cycle repeats the following spring.

A heavy infestation of apple maggot results in fruit that is dimpled, pitted, and inedibly rotten. Pitting on the skin of the apple is caused by the small punctures that the female makes as she lays her eggs, all 400 of them, and the feeding of the maggot can produce brown streaks or patches in the flesh. Open tunnels are possible, and the maggot's activities expose the apple to rot-producing microorganisms. The worst damage results in crops that are good only for livestock feed.

For further reading, see the Cornell Guide to Growing Fruit at Home and Apple IPM for Beginners from Cornell Cooperative Extension.






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