Fall leaf color changes
Leaf color change in August may seem premature, but some trees will turn from green to yellow or red. Decreasing hours of daylight is the usual trigger of phenomenon that becomes widespread in September and early October. Black ashes, the first trees to prepare for dormancy, are already turning bright yellow.
Not all leaf color changes are brought about by autumnal weather, some are caused by more mundane problems. Basal girdling by mice or other animals, standing water around roots, drought, and damage by insects or disease organisms can trigger bright color changes on some trees and cause people to wonder if an early winter is developing. Hardwoods, particularly maples, aspens and oaks, are showing foliar symptoms. Maples are prematurely showing fall coloration, especially the ones that are low on energy due to their extremely heavy seed production this spring. On aspens, entire branches are flagging out due to Hypoxylon canker, a vivid brown against the backdrop of other healthier foliage. Two-lined chestnut borer is active on oak predisposed by other circumstances and now showing red or dead leaves in the upper crown and live, green leaves below.
The butternut wooly sawfly, Eriocampa juglandis, was found on black walnut in mid-August in the Brainerd area. It feeds on leaves of butternut, black walnut and hickory. It is not considered a serious pest although it sometimes becomes locally abundant. The larvae have white heads with black eyespots, and their smooth green bodies are covered with white wool-like waxy material. When full grown they are about 3/4 inch long.
They overwinter in papery cocoons in the ground, then change into pupae and adults the next spring. Adults are small, black, fly-like insects with two pairs of transparent wings and eggs are laid in the midribs of leaflets.