We often think of spring and summer as prime time for insects — and it is. But, you know Mother Nature. She never follows the rules completely. With that, there are a few unwanted surprises even as the weather cools. Some caterpillar pests, like fall cankerworm and winter moth, emerge in fall and winter and can cause serious damage. This is especially true on properties that neglect autumn tree care, thinking the time for work in the landscape is done. These insects get busy right at that moment. Whether they’re munching on foliage or busy laying eggs, it’s an important time to undertake actions to manage pests populations.
Fall cankerworms emerge as adults after the first hard freeze in October through December. During this time, females crawl up the tree to lay eggs. While you should apply treatments in early spring when young larvae are present, autumn is equally important in management. Cankerworms must crawl up tree trunks to lay their eggs on small branches in the crown. Tree banding, sticky bands around the trunk, prevents the caterpillars from ascending into the canopy.
Cankerworms are notoriously voracious feeders and their presence can result in complete loss of leaves, or defoliation. During spring, most trees are usually able to regrow leaves. However, repeated years of infestations will cause upper branches to begin dying and eventually contribute to the tree tree’s demise.
Winter moth feeds on species like oak, maple, ash and apple. Adults emerge from the soil in November. The females lay eggs on bark, under bark scales and in crevices. These eggs overwinter and then hatch in spring. Like with cankerworms, tree bands in fall are one piece of the puzzle in a comprehensive management plan. These bands help trap insects as they climb and prevent egg-laying activity. Massive numbers of individuals can be captured this way. Good culture practices and appropriately timed treatments, including foliage sprays, will provide a further and robust measure of control.
Unlike the cankerworm, which is a native pest, winter moth was introduced to North America from Europe. Adults are whitish and about one-inch in length. The pale green caterpillars that emerge in spring, often called inchworms, are small, but mighty. They can quickly defoliate trees, especially during outbreak years.