No. 15/September 2, 2011
Fall webworm is common throughout the state. It lives as a group of caterpillars that spin a communal silk web. This silk nest typically encloses the end of the branch and associated leaves. The caterpillars remain in the webbing, feeding on these enclosed leaves. When the leaves inside the web are eaten, the silk webbing is expanded to include more leaves. Webs of mature caterpillars are typically 2 to 3 feet long.
Twig Pruner and Twig Girdler
Large numbers of branches from one to three or more feet long dropping from oaks at this time of year are likely to be caused by twig pruner or twig girdler. We have had a few calls about these insects in the last couple of weeks. In Illinois, these insects seem to prefer oaks, but will also attack elm, linden, hackberry, redbud, hickory, pecan, persimmon, honey locust, and flowering fruit trees. Twig girdler also attacks poplar and dogwood. Twig pruner also attacks chestnut, maple, sweet gum, sassafras, and wisteria.
Dealing with Drought
No drought is not a disease, but it can be categorized as an abiotic disease or condition. It seems as of late, I am having to write a lot of Plant Clinic sample reports that read, "suspect drought stress" or "water in times of drought." This is not surprising, as most of Illinois and other areas of the US are experiencing either abnormal to severe drought conditions.