Tree Defoliation in Massachusetts

Although seeing trees lose their leaves in the fall can be a beautiful sight, it can be quite disconcerting when it happens in the spring. Many parts of Massachusetts have seen a significant amount of defoliation this year because of high populations of two caterpillars: 1. forest tent and 2. Eastern tent. You may have even noticed the crowns of some of your own trees looking a little thin. In order to deal with these caterpillars effectively, it is important to be able to distinguish them a part.

1. Forest tent caterpillars - Forest tent caterpillars favor sugar maple, ash, and oak.
The larvae are mostly blue, with white spots down their backs that resemble a line of 10 to 12 white footprints. Despite their name, these caterpillars do not form tents. Mass quantities of forest tent caterpillars may form white mats of spider web like material that may cover sections of a tree trunk but these are not the same in appearance as the tents. They spin silk strings which act as parachutes that they use to move up and down from the crowns of trees.

USFS Forest Tent Caterpillars Pest Alert

2. Eastern tent caterpillars - The damage from Eastern tent caterpillars is pretty much limited to black cherry and or apple or crab apple trees. The larvae are dark in color and have a solid white stripe down the center of their backs. Eastern tent caterpillars construct tents or nests in the branch crotches of black cherry and apple trees.

USFS Eastern Tent CaterpillarPest Alert

The window of concern for trees is May and June when the caterpillar, or larvae, are actively feeding. By early July caterpillars will stop feeding and construct a cocoon. It is common for trees to survive defoliation. Defoliation is more of a threat to trees that have been subject to other stresses, such as drought. Defoliation limits tree growth and can have an impact on maple syrup production.

Since trees usually survive defoliation, the first management option to consider is doing nothing to manage the population. Environmental conditions and natural predators help regulate the cyclical populations. For more management options, contact a state service forester, private forester, or certified arborist: International Society of Arborists, Massachusetts Arborists Association, or Certified Arborists and Lawn Care Professionals.

It is also important to reduce additional stress on defoliated trees by avoiding disturbance to them. In the woods, be flexible when scheduling timber harvests. Postpone harvesting if populations build. Delay timber harvesting at least 3 years after the outbreak. A harvest can allow soil to dry, stressing trees. Also, by reducing the number of trees, you may get more insects on each remaining tree. On landscape trees, avoid root damage and pruning, and when applicable, provide adequate water during dry conditions or on newly planted trees.

Tree recovery from defoliation takes time, so be patient. First you can expect that defoliated trees will stored energy to develop a second flush of leaves in July to help produce more energy for the tree. Then, if no defoliations occur the following year, trees will begin producing more abundant leaves.