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The caterpillars are eating my trees.

I have gotten a few emails lately about catepillars that are causing damage to trees by eating the leaves. The cases seem to be scattered and isolated from what I have heard and seen. The Maine Forest Service have had reports of Forests Tent Catipillars being seen in Ashland and Island Falls in Aroostook County. There have been other reports of sightings in Topsham and Woolwich (Sagadahoc County). It is a distinctive, hairy blue-tinged caterpillar which can be recognized by the line of white to off-white “footprints” along the center of their backs. This is an outbreak prone species that can defoliate sections of hardwood stands quite rapadly. MFS thinks the populations may be increasing and that could be worrysome. The MFS has traps out and will report their findings a later date.

I remember an outbreak in Northern Maine in the 80s that defoliated large areas of hardwood trees. It looked like autumn came early that year. The roads had so many worms crossing them it made the roads slippery. The forest tent caterpillar often defoliates extensive areas. Forest tent Caterpillars strip the leaves of aspen trees and other hardwood species in the Northeast when outbreaks occur. Diameter growth may be reduced as much as 90 percent. Such defoliation kills few trees except for those that are suppressed. The favored hosts of this insect are broadleaved trees. In the Northeast, sugar maple and aspen are favored. They will feed on birch, cherry, ash, and ornamentals. Small trees can be protected by collecting and destroying egg masses, destroying colonies of young larvae at the end of branches, or killing larvae clustered on the trunks of branches during molting and resting periods. Chemical control is available. The catepillar will become a moth. Contact the Maine Forest Service for more information. Forest Tent Catepillars and a defoliated stand are in the pictures below.

I received an email the other day from someone who wanted to know about another catepillar that was defoliating a tree. He supplied a picture of the catepillar. These catepillars are not really catepillars. They are the larvae of the mountain ash sawfly. The mountain ash sawfly is a member of the insect family that includes bees and wasps. They feed exclusively on Mountain Ash. Though it is a defoliator, this insect seems to cause little lasting harm to mountain ash trees. It has been postulated that mountain ash sawfly larvae do not seriously deplete the food reserve of the tree because they feed primarily during the mid-growing season. To prevent defoliation of ornamental mountain ash trees, hand pick the larvae off the leaves and destroy them, or, apply an insecticide labeled for sawflies. Consult with Maine Forest Service before applying insecticide. Pictures of the mountain ash sawfly larvae are below.

There are other invasive forest pests that are currently affecting the forest trees in Maine. These include spruce budworm, browntail moth, european pine sawfly, hemlock wooly adelgid, oakleaf shothole leafminer, pine leaf adelgid, and the yellowheaded spruce sawfly. There are many more but they are not current problems. The emerald ash borer is in New Hampshire and could devestate the ash trees in Maine if it gets here. Another one is the asian longhorned beetle. It has been found in Massachuttes. This pest is a woodboring insect that attacks a wide range of hardwoods including all species of maple, birch, elm, poplar and willow. Damage by the beetle would impact the health of our forests, appearance of our neighborhoods and integrity of our infrastructure. In addition, it would lead to losses in the forest products industry, maple sugaring and tourism industries, and require a costly control effort. All citizens are being asked to be on the lookout for these pests. There are pictures and descriptions of the emerald ash borer and the asian longhorned beetle on the main page of this website.

For lates report of insect and disease conditions put out by the Maine Forest Service, use this link:

Photography Credits from top to bottom.

William Ciesla, Forest Health Mgt. Int.

Herbert A. "Joe" Passe

Steven Katovich, USDA Forest Svc.

James B. Hanson, USDA Forest Svc.

Next week (8/16/15): Correcting and Preventing Winter Injury to Trees and Shrubs

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