Pin Oaks & Willow Oaks; Stripped of Leaves in Late Summer
If the leaves of your pin oaks & willow oaks seem to be ‘disappearing’, this may not be your imagination. You may have a minor to moderate pest problem.
The Signs & Symptoms
Oak leaves disappearing (but not falling) in August through October. Huge, 2-inch long, ugly, black caterpillars crawling all over the place; especially up and down your oaks, and everywhere in between!
Orange-stripped oak worm (Anisota senatoria).
How it is Spread
Adults lay their eggs on the underside of leaves June to July. Caterpillars feed 5 to 6 weeks in July through September (and sometimes into October). After feeding is complete, mature larvae pupate in the soil, where they spend the winter. Thankfully, there is only one generation a year.
The Damage it Causes
Other than munching on your leaves, and squashing under your feet, not a whole lot. Even if they entirely strip a small tree, if it is moderately healthy, it will put on another crop of leaves. If it’s late in the season, it may just wait until spring.
While several broadleaf species may be vulnerable, they prefer red oaks; especially pin and willow oak.
Caterpillars are easily identified; 1 ½ to 2 inches long, black, with spins (horns) on its head, with 8 thin yellow to orange strips on it back.
1. Control. Severe outbreaks rarely last more than a few years due to natural enemies. For medium or large healthy trees, control may not be needed.
2. Treatment. For small or stressed trees, as well as high-value larger specimens, we can treat these systemically.
3. Poor Planting. Often, infected trees have more serious problems related to installation and cultural practices. Running over surface roots with your mower is not a sign of good health (or good for your mower). If you can not see your trees’ root flares, they may already be girdled. Girdling kills millions of our Upstate trees every year! Most of these problems can be corrected, if you don’t wait until it’s too late.