What Are Winter Moths?
Winter moths are invasive pests, originating from Europe and Western Asia. These insects were first found in North America in the 1930s; however, their population in Massachusetts exploded, causing home owners, property managers, and arborists’ tremendous stress, as winter moth larvae shredded and stripped the leaves off of their variety of deciduous trees.
Winter Moth Appearance
The winter moth larvae are pale green caterpillars with white stripes that run down either side of their body. The male winter moth have a light tan color, with four elongated wings that encompass their bodies. The wings of males gives them a “furry” look. Female winter moths have a grey color, as well as tiny scales that give off that furry look just like the males. Unlike the males, the females are incapable of flight.
Dangers of the Winter Moth
Winter moths are only dangerous to your trees in the larval, or caterpillar stage; however, you can treat for them in both the egg and caterpillar stage with either spray or injection treatments. The larvae or caterpillars once hatched will scale the trees searching for fresh buds and leaves they can start devouring. Once they find their fresh bud they wriggle between the scales of the newly blooming buds and begin feeding on the flower and foliar buds from within. The caterpillars don’t stop and will continue to migrate from bud to bud devouring as much as they can. Large populations can quickly defoliate trees which can result in limb or tree failure. Once the caterpillars become mature they drop to the ground and envelope themselves in a soft, wooly cocoon for pupation. When they finish pupation, they emerge from the soil throughout November and December but if the temperature remains mild they can be active into January.
Common Tree Hosts for the Winter Moth
White Elm Tree
Crabapple and Apple Trees
Prevention and Management Winter Moth
Winter Moths Can Be Controlled and Prevented
Winter Moth Prevention
It is best to prevent the pests from hatching with a horticultural oil treatment early in the spring. When the winter moths hatch they begin feasting on the budding leaves very early on, which can be extremely devastating to a tree. The winter moths will continue to feed and grow throughout the year. Treatments become more difficult as the winter moths grow, but it is still possible to control these pests. Spray or soil/trunk injection treatments with Spinosads and B.t.k can be used to defeat the caterpillars, which would otherwise feast on your leaves until dropping to the ground in May or June for the summer.
Treating and Controlling Winter Moth
In order to effectively treat winter moth, you first need to establish what stage the pests are in. Once you’ve identified the stage, then you can plan your treatment attack, but not without considering some other variables such as the size of tree to be treated, or proximity of homes or structures. These variables will help decide what type of treatment to use: topical spray application or injection treatment. For example, if you have an infested tree hanging over your swimming pool, you may want to consider an injection treatment.
It is important to treat for winter moths early in the year. Waiting until you physically see damage often means it is too late. Consider meeting with a Certified Arborist or Plant Health Expert in the late winter to discuss winter moth treatments.
If you have any questions or concerns about Winter Moth please contact us at 877-308-8733 or click the button below.
Pictured here are two examples of severe winter moth damage, with the culprit in the middle.
Editors Note: This post was originally published in March 2012 and has been revamped and updated for accuracy and comprehensiveness.