No. 12/July 30, 2018
Fall Webworm
Fall webworms (Hyphantria cunea) are communal caterpillars that spin silk into a tent-like structure at the tip of branches. These webs are often built around leaves they feed on. Fall webworms feeds on a wide range of deciduous trees and shrubs including, but not limited to, crabapple, redbud, sweet gum, maple and oak. As the caterpillars consume the leaves within the web, they will expand the web every week or so to include more leaves. The web of mature caterpillars can be 2 to 3 feet long.
Oak Wilt
Oak wilt is a serious fungal disease which continues to kill oak trees in residential areas, parks, farm woodlots, and forests throughout Illinois. The oak wilt pathogen was first detected in Wisconsin in 1944 and has slowly spread throughout the central and eastern United States, including across Illinois. Oak trees are the only known host, with oaks in the red oak group (pointed leaf lobes) more susceptible than oaks in the white oak group (rounded leaf lobes).
Weather is Conducive for Powdery Mildew
Based on the weather that we have had this past July, powdery mildew will be seen in more than just a handful of places. The six common genera of powdery mildew fungi in the Midwest all prefer warm, humid days. The spores germinate on foliage when the relative humidity is 23% to 99% but not in a free moisture (rain). Powdery mildew is a common fungal disease problem on many perennials as well as annuals, shrubs, turf and even trees. One plant can spread the disease very quickly especially in humid weather. Even though this disease can spread quickly over a plant, it doesn't normally kill one.
Protecting Trees During Construction
Are your clients taking the necessary steps to protect their trees during construction projects? Unfortunately, most homeowners don't consult with an arborist prior to starting their major projects. More often, they contact an arborist well after the project has been completed; when the tree starts to show signs of stress and dieback. Too often, the client mentions a recent construction or renovation project in close proximity to the tree. At this point, the damage has been done, and management options are limited. For many of these trees, the decline may have been avoidable with extra planning and work.
Butterflies and Caterpillars Abound
Caterpillars are abound this growing season leaving some to wonder, "Are they good or are they bad?" Most gardeners want butterflies and moths sipping nectar from their colorful blooms but are they willing to let the caterpillars take some hefty bites out of the foliage of their plants? Let us hope most gardener are willing, because without the fattening of caterpillars, we would not have our fancy-free winged beauties fluttering in the garden.