As if the onslaught of pests throughout the growing season were not enough, now our poor trees have to suffer yet another attack, and this one comes in the winter.
This invader hails from Europe, and made its way to New England via Atlantic Canada. It is now found throughout much of New England, including Rhode Island. If you look outside in the late autumn and early winter and see moths fluttering around, (they’re especially attracted to outdoor lights, including car headlights) you’re seeing winter moths, or Operophtera brumata. The moths are most active from November to January. Only the males fly. The females can be found at the bases of trees, where they emit pheromones to attract the males. The eggs overwinter on the trees, and hatch in the spring, when the temperature warms to around 55F.
Winter moth larvae burrow into buds – especially those of fruit trees like crabapple. Other hosts include oak, maple and white elm. At best, the larvae munch on the buds so that when they finally open, the leaves are tattered and sparse. At worst, they will defoliate entire trees. If the trees suffer repeated attacks and defoliation over even a few years, they will die.
Several natural controls have been used to control battle these pests. These include parasitic flies and wasps, and ground beetles. Dormant oil spray has been quite successful in killing the eggs before they hatch. Good old bacillus thuringiensis, or B.t (kurstaki) kills the larvae when they are not inside the tree buds. Spinosad is a widely used bioinsecticide that is said to work well.
It is important to remember that defoliated trees are severely stressed. Experts suggest making sure they get plenty of water especially during dry spells to encourage the production of a second set of leaves. Here in Rhode Island, we had a very warm autumn, and before we started getting some snow, I was seeing the moths all over the place. This does not bode well for our trees this coming spring.