By Katie Drewitz, U of M Extension
As the apples on your trees continue to grow, there are numerous factors that we need to consider. The apple maggot (Rhagoletis pomonella) is the most important insect pest to Minnesota-grown apples and typically 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, the larvae feed on the apple for three to four weeks. The dropping of the apple to the ground signals the larvae to leave the apple for the soil where they will pupate and overwinter.
Harvesting apples before they fall to the ground, and keeping apples picked up from the ground, 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 in the skin of the fruit. The pulp breaks down, discolors and starts to rot as a result of the larvae tunneling through and eating 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, if anything, 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. This process is time- and labor-intensive. Kaolin clay is a second method that 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 adult 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 read and followed.
More information about the life cycle, prevention, and treatment of apple maggots can be found at www.extension.umn.edu.
Some information in this article was gathered from Jeffrey Hahn, Extension entomologist; Michelle Grabowski, Extension educator; and Jill MacKenzie.