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Tent Caterpillars on Trees and Shrubs (6/04/20)

We’re beginning to see damage from tent caterpillars in eastern North Dakota and western Minnesota. Tent caterpillars eat foliage and in the worst cases, can defoliate entire trees like this chokecherry.

We’re beginning to see damage from tent caterpillars in eastern North Dakota and western Minnesota.  Tent caterpillars eat foliage and in the worst cases, can defoliate entire trees like this chokecherry.

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Eastern tent caterpillar (Malacosoma americanum) is the damaging agent on this chokecherry.  These insects feed on the leaves during the day, but spend the night back in the communal nests, located in branch crotches.  These nests provide a great place to apply control efforts. Some trees attacked by the eastern tent caterpillar include chokecherry, pin cherry, and occasionally other hardwood species. The simplest method of control is to simply remove the nests and destroy them.  The bacterial-based pesticide Bacillus thuringiensis var. kurstaki (Btk) works well to control young larvae, while pyrethrins or synthetic insecticides are needed for older larvae.  Do not take a blow torch to the nest, as that will also damage the tree.

Forest tent caterpillars (Malacosoma disstria) are another defoliator found throughout North Dakota.  These insects appear at about the same time as eastern tent caterpillar, but have a much broader host range and no communal nest in trees.  We’ve seen them on linden, ash, apple, oak, maple, lilac, rose and other deciduous trees and shrubs.  Populations of this insect cycle up and down, so some areas are experiencing large outbreaks right now, while other areas have very little pest pressure.

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Control measures for forest tent caterpillar are the same as those for eastern tent caterpillar.  For small infestations, the larvae can easily be picked off the tree and destroyed.  Other insecticides available to homeowners include:  acephate (Orthene), azadiracthin (Azatin), carbaryl (Sevin), esfenvalerate (Bug-B-Gon), malathion, permethrin, spinosad (Conserve), or other insecticides registered for trees. Always read, understand and follow the insecticide label directions.

 

The caterpillars will complete their feeding in mid-to-late June, so control measures should be applied as soon as possible.

 

Joe Zeleznik

Extension Forester        

   

Janet J. Knodel

Extension Entomologist

 

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