Winter Moth Caterpillar
The winter moth Caterpillar has been a very destructive pest in eastern Massachusetts and beyond. It is important to know that this caterpillar attacks trees, shrubs, roses and edibles very early in the season often before the leaf buds fully open. This tiny caterpillar hatches and climbs up the plant to begin feeding inside the bud as it opens. Inside the bud is a natural protection against predators such as birds and insecticides. However it is important to treat susceptible plants as soon as you see the buds opening and leafs appearing if the Winter Moth is suspected. One way sign Winter Moth caterpillars are present is the silk that looks like spider web strands. It is hard to see unless you look at the leaves closely, you will see the shiny silk criss-crossing between leaves. Also look for small holes in the leaves. The caterpillars are often too small to see and they blend in with green leaves. The best spray available is Bonide’s Captain Jack’s Deadbug Brew. This can be applied when buds start opening to kills some of the early hatching caterpillars. Waiting until leaves fully emerge gives more surface area to spray and it is often the most effective stage to spray, but if you wait too long there will be significant damage to leaves and flower buds. Even if you kill all the caterpillars on the treated plant more caterpillars may come back swinging from other larger trees after the spray washes off in a strong rainstorm. Re-applying one or two more times is usually sufficient. Try to avoid spraying when trees are in bloom. If you have to trees in bloom, spray at night after the sun is down. The active ingredient is Spinosad and it is less toxic to bees after it has dried, but it is best to spray trees before they bloom or after the flower petals drop. Bees are very important and should be valued!! The other spray that is sometimes mentioned with Winter Moth Caterpillar and other early feeding caterpillars is Horticultural Oil or Bonide’s All Season Oil spray. This is an effective spray that kills any overwintering eggs on a tree or shrub. It should be applied in late March before the eggs hatch. BT is another safe spray with supposedly less bee toxicity but it is not always as effective, especially when the caterpillars become larger.
The most susceptible plants for Winter Moth Caterpillar are flowering and fruiting Cherries, peaches, apples, crabapples, maples (shade trees & Japanese), birches, roses bushes, blueberry bushes and more.
For more info on Winter Moth Caterpillars including the different sprays and application techniques check out my video on YouTube.
Winter Moth Video by Chris Kennedy, MCH