Last summer, friends brought my wife and I two big bags of apples from their tree. They were quite large and looked wonderful, but we soon discovered that most of them were inedible because they were full of dark-brown tunnels — a sure sign that they were infested with apple maggots.
The life of the apple maggot begins with the maggot fly laying eggs on the surface of developing apples. The eggs soon hatch and the tiny maggots burrow into the apples and feed, creating multiple tunnels in the fruit. As the apples mature they fall to the ground, and that is the message to the maggots that it is time to leave — and they do — burrowing about five cm into the ground where they go through another stage of development and evolve into pupae which overwinter in the soil. The pupae turn into flies in late spring and emerge from the soil about mid-June, just when the apples are developing on the tree. The adult flies then begin the process all over again by laying eggs on the fruit.
There are two lines of defence, and using both will ensure that the maggot problem in your apple tree is kept to a minimum. First, conscientiously pick up apples as soon as they drop to the ground because the maggots do not stay in the fallen apples very long before burrowing into the soil. The best thing to do if the apples are infested and you are not going to use them is to pick them before they fall and dispose of them (not in the compost bin but in a tightly sealed garbage bag). Even if you have no infestation and are harvesting and using your apples, there are always a few that fall from the tree. Pick them up and dispose of them; don’t let them lie on the ground for any length of time.
Secondly, prevent the maggot flies from laying their eggs on the apples in the first place. To do this you have to construct decoys so they lay their eggs on the decoys and not on the apples. The best decoys are round balls that are about the same size as the apples and bright red. The maggot flies are attracted to red since it is the colour of mature apples. Old red Christmas balls can be used but any balls would do, whether Styrofoam or plastic. If they are not red, paint them with some shiny red spray paint. Then coat the balls with a product called “Tanglefoot,” a sticky substance that will trap the flies when they land on the balls. This is the same product that is used to band elm trees to protect them from Dutch elm disease. It is very gooey and sticky so take care in handling it. Finally, tie the balls to the apple tree, concentrating them on the south and west sides which are favoured by the flies and where the reddest apples are likely to be located. Hang them with wire or string so that when they sway in the wind they will not strike branches or each other.
If you have a heavy population of maggot flies the decoys will have to be replaced every so often as they will become too cluttered with dead flies and not be attractive to new ones. Keep the balls on the tree until the apples have all been picked.
There is nothing more frustrating than to have a crop of apples destroyed by insects. Hopefully by taking preventive measures, your apples this year will be free of the pesky maggots that destroyed so many last summer.