While walking around my pecan trees checking to see if any nuts are hitting the ground yet, I noticed I had a good many pencil-sized limbs on the ground. They had dead leaves attached and looked as if someone had sawed them off with a pruning saw. This is the work of the long-horned twig girdler beetle. It is a pest of pecan and other hickory trees, but also attacks oak, persimmon, elm, poplar, gum, basswood, honey-locust, dogwood and an occasional fruit tree.
The cut end of the limbs are as neat as if cut with a pair of hand pruners. I find this amazing, but insects are indeed amazing creatures.
Adult twig girdlers are about 1/2 inch long and brown with irregular patches of gray hair, which allows them to blend with tree bark. They have antennae that are as long, or longer, than its body.
Females breed in late summer and begin selecting twigs to lay their eggs. She chews around the entire twig until it is almost separated from the tree. This is called girdling. She will then lay eggs in the dying twig. You may or may not notice the twigs dying on the tree. When the winds pick up, these damaged twigs will break off and hit the ground. That is when you will notice the damage. I usually see stems with dead leaves, but occasionally I will see a stem that still has green leaves and know they are busy chewing and laying eggs in my tree.
Twig girdlers have little impact on large trees. Pruning a twig here and there is no reason for concern. It just makes a bigger mess to clean up. However, when they chew the terminal out of a smaller tree, such as a pecan or Asian persimmon, it can lead to misshapen or multi-trunked trees and slow tree growth.
If I had a tree nursery, I might apply an insecticide to attempt to kill the adults. In the landscape, you are not going to know they are present until the damage is done. About the only thing that can be done to reduce the numbers of these pests is to pick up and burn (or otherwise destroy) the twigs you collect. Those stems are full of eggs for next year.
If you live close to the woods you will always have some twig girdler activity. This may be more prevalent in some years depending on environmental conditions.
From my observations, my guess is that the pecan crop around here is less than average. Out of about nine trees that I have access to, only two have a decent crop. Some trees had a crop but scab and powdery mildew pretty much took them out of the picture. Hurricane Michael did a great deal of damage to Georgia’s pecan industry, so prices may be a bit higher as we head into pecan pie season. Georgia is the number one pecan production state in the U.S.
If you need information on pecans, such as pecan nurseries, recipes, nutritional value of pecans, etc., check out the web page of the Alabama Pecan Growers Association. They have a great deal of information on commercial production and useful information for homeowners as well. Just Google the site.
If your trees didn’t perform well this season, remember that pecan trees are alternate bearing. If you haven’t applied lime around your trees in a while, they probably need it. You can always pull a soil sample to check soil pH. Now is the time to do this. Fertilize them next spring with a pecan special fertilizer or any complete fertilizer such as 8-8-8. Add about one to three pounds of zinc every three to five years around the dripline of your trees if the fertilizer does not contain it. How you maintain your trees this year impacts yields next year and further down the road.
Pecan pie season is finally here. Enjoy!
Dan Porch is County Extension Coordinator with the Blount County Extension Office. Dan lives in and loves Blount County and is available to answer your questions about conservation, agriculture, natural resources, and gardening. He can be reached at (205) 274-2129 or firstname.lastname@example.org.