Defoliators and other fall concerns

By John Fulton

[September 14, 2011]  Most fall defoliators come to us as the larval stage (caterpillars) of a moth. When we talk about controls of the larvae, the fact that they are larvae of moths or butterflies makes them susceptible to the use of Bt products such as Thuricide. Other control options include the standbys such as Sevin, permethrin, bifenthrin, Othene, malathion and others.

The way that insects live also dictates some of the control do's and don'ts.

Fall webworms live inside a web all the time. They actually expand the webbing as they need to have more leaves to eat. They are usually worst on fruit and nut trees. You can even clip the nest (and the branch it is around) off the tree and burn it. I guess this tells you that defoliation caused by the insect isn't that great a threat to the tree or you wouldn't cut the branch area off. If you want to spray fall webworms, you need to get the spray through the web. This may be a little harder than you think. If you don't have enough pressure, the spray just runs off the webbing.

In the case of eastern tent caterpillars, they hatch out of a common nest. They then leave the nest to feed but generally return in the evening to congregate in the area of the nest. They are not covered by webbing, and the time they are congregated is a great time to spray since they are usually in one area on the trunk or main branches of trees.

In summary, control of fall defoliators usually isn't justified from the plant's standpoint. Forested areas have heavy pressure from this group of insects every year, and the trees are still thriving. The exception is newly transplanted or struggling plants. If appearances are important, consider a control spray.

Other fall items

You may have noticed a very large number of brown needles on evergreens this fall. That may even have translated to large piles of needles under your evergreens in the past few weeks, especially white pines. Not to worry. Evergreens usually keep only one to four years of needles on the ends of branches, or one to two years of growth for white pines. Depending on the weather, the old needles will turn brown and drop off. Usually this is a gradual process that isn't noticed too much. This year it happened all at once, mainly due to the hot and dry weather. If the buds on branch tips are plump and green, odds are your tree is fine.

Several calls have come in concerning the proper time to prune or cut things back. Let's start with some flowers. Keep in mind that perennials keep building their food reserves until all the leaves and stems are brown. For peonies and other similar flowers, you want to wait until all the above-ground plant parts are brown. Then you can mow them off or cut them at ground level. This same principle goes for most perennial flowers: Wait until the above-ground parts are no longer green. For trees and shrubs, pruning is best done at other times. Flowering shrubs should be done after they flower; high-sap-flow trees are best done in December; and most other trees are best done in February. The evergreen trees and shrubs are best done in late June.

Crabgrass is nearing the end of its life cycle. It comes up from a seed about the first of April each year, depending on temperatures. Seed has been viable for several weeks already, and that is what will make next year's crop. The seedling germination inhibitors do the best job on the annual grasses, and they can stop the cycle anytime you apply them. For now, let nature run its course since you really don't have any options anyway.

[By JOHN FULTON, University of Illinois Extension]