The waxy coating of wolly aphids left on a Red Oak leaf.
A little over a month ago, I was looking around making notes about the needs of the gardens at Minnetrista, and I noticed what looked like little bits of cotton spread out on the ground below an oak tree. At first I thought a mower had hit a cigarette butt that someone littered, but after a closer look, that wasn’t what it was. This cottony looking substance was a sign we had a wooly aphid infestation.
Wooly aphids are a common pest insect that feed on many different types of trees in our area. Like other aphid species, wooly aphids feed on the plants they live on by piercing the plant tissue with a needle like mouth part, and then sucking out the sap. Wooly aphids will feed on leaves, stems, and twigs.
The signs of wooly aphid damage are also similar to other aphids’ species and can include the following:
• Stunted, curled, yellowed and distorted leaves.
• Honeydew, the sticky substance aphids secrete as waste, can be found on surfaces below the tree and leaves may be sticky.
• Sooty mold, a black fungus may be present on leaf surfaces. Sooty mold feeds on the honeydew.
• Usually easily seen groups of aphids on the underside of the leaves.
In the case of wooly aphids, you will also see the sticky, white wax substance they excrete for protection on the leaves and bodies of the aphids. You may also notice the white wax on the ground below the tree, as I did at Minnetrista.
Luckily this is the case with other wooly aphids. Aphids will rarely cause enough damage to a tree to kill it, and the infestations tend to not happen yearly.
You can treat for wooly aphids, but most likely it would be a job that would need contracted out. Most trees are going to be too big for spray equipment that is available to the homeowner to reach. If you do treat, garlic sprays may be an option.
Your best option is to have time and patience, and let nature take its course. Many insects and birds feed on aphids, and will likely rid you of the pest over time.