The calls are coming in about bugs up in the trees.
This is fall webworm season. If the leaves of a tree are enclosed by webbing in the fall, the caterpillar probably is fall webworm, which feeds on over 100 species of trees.
Eastern tent caterpillars show up in early spring and build their webs in the crotches of limbs, so timing and placement of the web is wrong for eastern tent. The other caterpillar that we keep an eye peeled for is the gypsy moth, which has devastated forests in the northeastern United States but has not established itself here. Gypsy-moth caterpillars would be present in the spring and start pupating in May, so gypsy moth likely would not be present as a caterpillar in summer or fall.
The Georgia Forestry Commission sets traps every year to monitor the presence of the Asian and European strains of the insect. Those found here usually have hitchhiked on cars, trucks and campers travelling south into the state.
All this is a long way of saying that if you call me about caterpillar webs covering leaves in your tree, I don’t need to inspect it to identify it. It’s fall webworm.
So what do you do about it? Unless it is in a commercial orchard or plant nursery, you generally can ignore it. Native trees and native insects have a long history together.
Broadleaf trees store enough energy that they can experience complete defoliation three years in a row and come back. Losing a few leaves late in the year likely will not cause enough energy loss to be noticeable. Tree owners who don’t know how trees work have a long history of turning something that is not a problem into one by doing something that makes the human feel better but actually hurts the tree.
The most-common reaction from people who see defoliation on their tree is to throw fertilizer on the tree to force new leaves onto it. Heavy nitrogen fertilization, especially in the late summer and autumn, is a great way to starve a tree to death, set it up for winter injury and call more bugs to the tree. This is one of those cases in which letting nature take its course provides the best result.
The other webbing showing up on trees is a silvery web that appears on the trunk and large limbs of a tree. This is one of the most harmless critters one can find on a tree, but it generates more panicked calls than any other. Yes, it is bark-lice season. Except that they are not lice. Technically, they are psocids, pronounced “so-sids.” These little insects graze on algae and lichen on the bark of trees. The webbing helps obscure them from predators. They do not hurt the tree, you or anything other than the algae and lichen on tree bark. Again, something you can ignore with impunity.
Ants also are harmless critters that seem to get a lot of unnecessary attention when people finally notice that they are in their trees. Ants in trees usually are herding aphids in much the same way a dairy farmer herds his cows. Dairy farmers move their cows from pasture to pasture and protect them so the farmer can harvest the milk. Similarly, ants herd and protect aphids on trees for the sugar the aphids produce. Aphids feed on plant sap. All organisms have a carbon-to-nitrogen ratio. For every so many carbon atoms they consume, they need a nitrogen atom to go with it so they can make their enzymes, DNA and proteins.
Moms put it a lot more succinctly: “You can’t just eat french fries — you have to eat the hamburger, too!” The fries are the carbon, and the hamburger is the nitrogen. There is little nitrogen in plant sap. Aphids have to process a whole lot of sap, and a whole lot more carbohydrates than they need, to get a little nitrogen. All that excess carbon gets processed right through the aphid and leaves in a concentrated form. The result of this is the stuff that comes out the south end of a northbound aphid is almost pure sugar, which is a food source for the ants that prey on just about anything else that moves to get their nitrogen.
If you park your car under a tree with aphids on it, the sticky “honeydew” (rhymes with “aphid poo”) will rain down on your car and stick like glue to the finish. (There’s a Brad Paisley song in there somewhere.) Soaking the surface in water and rinsing frequently to dissolve the sugar is the easiest way to remove the honeydew. If left long enough, a fungus can grow on the honeydew. This sooty mold fungus is what turns the leaves of trees black when honeydew falls on them. You can wipe it off with your finger to reveal the leaf beneath. The leaves still are functional, just shaded.
That makes complaints about sooty mold on plants and property much ado about aphid poo. These are the things that rattle around in my head.