egg masses and predicted that we would be seeing an severe outbreak of this pest this fall. And sure enough, if you didn't spray your trees back in August, your trees are probably covered with webs.
The photo at right shows a young tree in covered with webworm colonies. When I look at this picture, two questions pop into my mind : 1) Will webworms cause long term damage to this tree? and, 2) Why do the webs look so much bigger than usual?
Fall webworm larvae can totally defoliate a young tree by mid-September. However, branches and dormant buds are untouched by the caterpillars. This means that limbs, defoliated in early fall, will typically remain in a dormant condition until next spring. The true long-term impact of webworm defoliation is a little harder to see.
Losing leaves 6-8 weeks early means less time to build carbohydrates via photosynthesis and ultimately less stored energy for budbreak the following spring. The result is a weaker spring flush of growth and a slow down of tree growth rate. Fortunately, trees can overcome this lag in growth rate by supplying trees with ample soil nitrogen in early spring.