We’ve had dozens of people come in to the nursery in the last three weeks with jars, baggies, branches, and leaves asking what’s defoliating their trees. The likely answer — winter moth caterpillars (Operophtera brumata). This is a relatively new pest that since its introduction is claiming more and more of Massachusetts as its chomping grounds. These green inch worms grow from tiny tiny to over an inch long almost right before your eyes — eating so voraciously as they grow that they can completely defoliate a tree in days. What to do? Three things.
First, you should confirm that you have wintermoth and then you’ll have to spray. This is the only way to knock down the population of this pest to manageable proportions and will help protect not only your own plants but also those in your neighborhood. Go to www.umassgreeninfo.org for pictures and for the most up-to-date and reliable information on what to spray and when. There are a range of options that can fit your definition of environmentally responsible.
Second, help a damaged tree put out new leaves by watering deeply once a week.
Third, be on the lookout starting early next spring for the next generation — they will most certainly reappear. But next time around you’ll be ready for them!
Weston Nurseries, Inc.
katbergmann
waynemezitt
Melissa
Ann W
Is it too late to spray now?
If you still find caterpillars on your plants, you can still spray. Soon the remaining caterpillars will finish eating and lower themselves to the ground where they will pupate beneath the soil surface; but they’ll emerge as adults next spring. Start looking for them in early April.
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I have heard that the winter moths crawl up the trunk of the tree in early winter and some people wrap sticky tape on the trunk to trap them. Is this valid?
Hello,
Thank you for the question! Using a barrier wrap has limited effect. With large female moth populations the barrier becomes clogged quite quickly and the rest of the females simply crawl over those that were trapped. Still, some are trapped and killed and prevented from laying eggs, just not enough to make a big dent in the population. Relative to the labor involved in setting up the barriers, especially if many trees are the target, there are more efficient methods for knocking down the population. If you do use a barrier, note that you should never apply the sticky trap material itself to the bark, only to the outer surface of the material the strip is made from.
Good luck!