Q: I finally harvested the apples from my Fireside tree this week, and almost all of them look like this — pitted and shrunken, with brown streaks inside. What happened? Are they still edible?
A: These are the signs of apple maggots. They are a common pest. You may never notice them, but adult flies will show up during the summer and pierce the skin of developing apples and crabapples to lay their eggs. The maggots then tunnel into the flesh of the apple. When the apple falls to the ground, the maggots emerge and pupate in the ground. New adults emerge from the soil the following summer.
You can still eat the apples. Any worms that are still inside will be so small — about ¼ inch at most — that they’ll be difficult to see. It won’t hurt you to accidentally eat them. Apples that have been hit by apple maggots tend to be unattractive, though, so people often make them into sauce, jelly or cider. They won’t store well.
Preventing maggot infestations is possible but requires a bit of work.
First, immediately pick up any apples that fall to prevent maggots from emerging and pupating in the soil. This will help reduce next year’s maggot problem, but if your neighbors have infested trees, it won’t help much.
Second, hang traps in your tree in late June. These are red spheres coated with a sticky substance. You can buy them or make your own with a red wooden or plastic ball or a red apple from the grocery store. Traps will reduce but won’t eliminate the maggot problem. They also let you know whether you have apple maggots to begin with, so you can decide whether to use other treatments.
An effective, chemical-free way to prevent maggots is to bag the apples while they are still small. Slip a plastic sandwich bag over the apple and put a staple on either side of the stem to hold it in place. Cut the bottom corners off to let moisture drain. When the female apple maggot flies appear in July, they won’t be able to pierce the bags to lay eggs. It looks strange on the tree, and it’s a bit time-consuming, but bagging does work against maggots and other pests.
You can also spray the apples with kaolin clay, but you will need to reapply after rain. And there are some pesticides that are effective against apple maggots. They’ll also need to be sprayed more than once during the summer.
There’s more information about apple maggots, including more detail on traps, bagging, and sprays, here: extension.umn.edu/yard-and-garden-insects/apple-maggot#sticky-traps-1814712.
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