Q: We have an enormous old pecan tree on our property. While planting some vegetables in mid-summer, we noticed some horrible looking leaves on the ground.
We aren’t sure if it’s scab or something worse. Our main concern is if it could destroy the tree – it is poised to fall right through the full length of the house!
A: You see scary…I see fascinating! The bumps are harmless insect galls growing on the leaves. The galls are caused by pecan phylloxera, aphid-like insects that emerge in spring and infest leaves and twigs. Big populations of this insect can cause loss of the pecan crop for the current year and also the following year.
If you only enjoy your tree for its foliage and not the nuts, nothing needs to be done. Phylloxera populations vary widely from year to year, depending on weather and predators. If you want to harvest nuts, use a hose-end sprayer designed for trees to apply Green Light spinosad in early April and again two weeks later.
Carbaryl (click for sources) can be used to control phylloxera. Timing the pesticide application is critical. You won’t get ANY control if you wait until you see the galls.
Spray your tree about the time the pecan buds show a half-inch to three-quarters of an inch of new growth, around the first week in April.
To get the spray way up in the tree, use a hose-end sprayer designed for tree and shrub application. Even if you can’t reach the entire tree, some control is better than none.
Phylloxera are delicate insects and usually do not spread very far. Good control one year will often keep phylloxera damage low for several years unless infested trees are near.