By Katie Drewitz, University of Minnesota Extension
PRESTON and CALEDONIA, Minn. (07/19/2022) — 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 first (depending on the weather) 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 signifies to 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 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 you choose 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 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 adult apple maggots are present, so you must use traps to help you decide when to apply. Always read and follow pesticide labels.
More information about the life cycle, prevention and treatment of apple maggots can be found at www.extension.umn.edu. For more information please reach out to your local County Extension office. Residents in Fillmore and Houston counties can email email@example.com or call 507-765-3896 or 507-725-5807 for assistance.