Also known as cigar rollers, leaf roller aphids cause a very peculiar symptom on Oaks. The leaves look as if they have been converted into a poorly rolled cigarette (with only exoskeletons inside instead of tobacco 🙂 ). Typically the damage is done in early spring when the leaves are emerging and the tissue is soft and new. This makes the aphids difficult to diagnose early since most lay people feel everything is normal when the leaves are small in the spring. However, 2 months later, when the leave never develop to their normal shape, the diagnosis is unmistakable. If your tree gets infested, don’t freak out. The damage is not fatal 90% of the time.
The unfortunate scenario when your tree is afflicted with roller aphids is that the leaves will look bad for the entire growing season. The foliage will produce a reduced amount of sugars compared to normal, but it is not a complete loss. The important thing is to do an early preventative treatment the following year to make sure you don’t get back to back infections. Recurring stresses will have a negative impact on your tree. A regular fertilization and inspection regimen should be engaged when you recognize any significant insect attack such as leaf roller aphids.
I have seen these aphids affect nearly all species of oaks, however they are most common on live oaks and Monterey oaks. The best way to treat aphids is with immidicloprid or another system insecticide. The treatment we use is a liquid solution of immidicloprid poured at the base of the tree. The tree absorbs the treatment and is protected for one year against many insects, including the leaf roller aphid.