The winter moth, or winter worm, population has exploded in our region over the past few years. These pests can cause serious defoliation to your trees; however, with proper management techniques, winter moths can easily be controlled and prevented.
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.
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.
Let’s consider the calendar year here in Massachusetts. If we’re experiencing an average year temperature wise, you can expect winter moth eggs to begin hatching between late March and the third week in April. If we’re having an unusually warm late winter and early spring they will hatch sooner. Conversely, a colder winter and early spring will delay their hatching.
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.
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.
Pictured here are two examples of severe winter moth damage, with the culprit in the middle.