Q: We have two large pecan trees that are too large to spray. Every year the pecans have a small hole with a white worm in them. What can be done to prevent this?
A: You have pecan weevils in your pecans. The adult female weevil is a beetle-like insect that emerges from the ground in early August each year. She crawls or flies up into the tree and drills a hole through the shuck and into the nut, where she lays eggs.
The grubs that hatch afterwards feed on the nut interior. Some escape through a hole they bore in the shell while others remain inside.
It’s impossible for a homeowner to spray insecticide over an entire tree but there are some strategies that might help control the weevils.
First, pick up and destroy all damaged nuts each year.
Second, apply in late July a foot-wide band of sticky material like Tanglefoot (click for sources) around the trunk six feet above ground. This will catch weevils that crawl up the trunk into the tree. To keep the material from staining the bark, wrap wide masking tape around the trunk before spreading it.
Third, spray carbaryl (click for sources) as high as you can reach in the tree beginning the first week of August and repeating every 10 – 14 days until shucks begin to open.
Also see Pecan Weevil Control