University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article


LANDSCAPE PLANT PESTS
 
Dr. Leonard Perry, Extension Professor
University of Vermont
 
 
Birch leafminer and borer, eastern tent caterpillars, and fall webworms are some of the common pests on trees and shrubs in landscapes.  Knowing these, and their least toxic controls, will help you have healthier plants with the least harm to the environment.  A New England website of Extension services (pronewengland.org) provides some photos, information, and further resources on these and other garden problems.

Birch leaf miner larvae feed inside birch leaves, causing tan-colored blotches.  If severe infestations, leaves may be almost totally brown.  Gray birch and paper birch are most susceptible, with other birches much less so.  It is much easier to control adults in spring as the new leaves emerge, before they lay eggs   The larvae that hatch, being inside the leaves,  are much harder to control.  If this pest is severe for several years, trees can be weakened and attacked by the bronze birch borer.

The bronze birch borer is the larva of a beetle which tunnels through the bark, eventually resulting in tree death.  This happens from the borer eating and cutting off the vascular tissue,
that part of the tree that conducts water and nutrients below the bark surface.  This is a form of “girdling.”  Once you see raised areas in the bark, control may be too late.  Most commonly injured are paper and white birches, with other species more resistant.  Since a healthy tree is seldom invaded, this is the main means of prevention.  Preventing injury from birch leaf miner helps, as does not pruning trees during summer when adult beetles are flying about. Larvae, once inside trees, are difficult to control.

Eastern tent caterpillars are recognized by many from their white webbed “tents” in branch crotches, teaming with black caterpillars.  These insects hatch from eggs in early spring as buds open on apples, crabapples, cherries, and their relatives.  They emerge from the nests on warm days to feed on leaves, at which time they can be controlled with sprays such as insecticidal soap.  Nests can be pruned out in early summer and destroyed, as can the shiny black egg masses (about one inch long) found on twigs in winter.

Fall webworms are similar in that they make web nests, but these are on branch tips and begin in mid to late summer.  There often are several per plant, compared to one for tent caterpillars.  And the larvae of fall webworm feed from within their silky nest, expanding the nest down the plant as they feed.  Nests can be pruned out as for tent caterpillars.  Don’t use fire to destroy these or tent caterpillar nests, as the fire may do more damage to the host plants.  Many different plants host this pest, including birch, lilac, crabapple, and cherry.  Since feeding is late in the season, it is more an aesthetic problem than harm to plants. 

Other potentially serious pests to watch for on your landscape plants include the Japanese beetle, viburnum leaf beetle, black vine weevil, and white pine weevil.  More on these pests and others, and their controls, can be found at the University of Massachusetts landscape website (www.umassgreeninfo.org).

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