By Katie Drewitz,
U of M Extension
Start monitoring for them now.
The apple maggot (Rhagoletis pomonella) is the most important insect pest to Minnesota-grown apples and starts to become active in July. Heavily infested apples are distorted, inedible, and will have limited use. There are control options available for all sizes of growers and hobbyists.
To understand control options and infestation we must first understand the life cycle of the apple maggot. Adult apple maggots begin to emerge from the soil starting around July 1 and will continue through September. Adult flies leave to feed in bushy areas, then return to lay their eggs under the skin of the apples. Once the eggs hatch they feed on the apple for three to four weeks. The dropping of the apple to the ground signifies the larvae to leave the apple for the soil where they will transform to pupae and overwinter.
Keeping apples picked up from the ground, and preventing excessive numbers of apples from falling in the first place can help to reduce next year’s apple maggot population. Apples infested with apple maggots will be pitted and misshapen. Each time a female fly lays eggs a dimple forms. The pulp breaks down, discolors, and starts to rot as a result of the larvae tunneling through the flesh.
Using an apple maggot sticky trap will help you to know if you have a presence of apple maggots in your trees. This will help you to assess what to do for control options. There are a few control options available and which one to use depends on your desired outcome. Bagging is a method in which each apple is enclosed in a bag which remains there until harvest. Kaolin clay is a second method and can be applied to all parts of the tree including the fruit. The apple maggots are attracted to the red color of the fruit. The gray that the clay provides makes the fruit less attractive to the insect. The clay can be washed off in the rain which gives it limited long-term effectiveness without -reapplication. Pesticides can also be an option. However, pesticides only work when the apple maggots are present, so you must use traps to help you decide when to apply. When using a pesticide the label must always be followed.
More information about the life cycle, prevention, and treatment of apple maggots can be found on at www.extension.umn.edu. Some information in this article was gathered from Jeffrey Hahn, Extension entomologist; Michelle Grabowski, Extension educator; and Jill MacKenzie. For more information on this or any horticulture, small farm and local foods topic you are welcome to contact Katie Drewitz, local Extension Educator for Stearns, Benton and Morrison counties at (320) 255-6169 ext. 1.