WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Tent Caterpillar & Fall Webworm

(Various Species)

Insects & Invertebrates

 

Tent Caterpillar

 

Symptoms

Larvae feed in colonies on the foliage, often skeletonizing leaves. If left unnoticed, colonies can defoliate entire young bushes. Except for the forest tent caterpillar which does not build tents on blueberry bushes, the larvae live in large, untidy web shelters built around a segment of the bush. These houses will also interfere with harvesting if not treated.

 

Identification

The larvae of forest tent caterpillars have a row of white diamond shaped markings along the top of their bluish-grey bodies. Western tent caterpillars have a row of blue spots along the top of their bodies with orange spots on each side of the line; their bodies are hairy and yellowish-brown. Fall webworm caterpillars are covered with yellow-orange hair growing from black and orange bumps. The adult moth is active at night and is rarely seen.

 

Tent Caterpillar

 

Life History

Western and forest tent caterpillars overwinter as eggs in ring shaped masses on year old wood and create tents from May to June.

Fall webworms overwinter as pupae in the leaf litter or in the soil below the plants and create tents from the middle of July to the middle of September.

 

Monitoring

These caterpillars are known as generalist feeders and for this reason they are often found around the peripheries of the fields adjoining to alternate hosts. Many species will disperse as tiny larvae on wind currents deeper into the fields, so monitoring should not be constrained to field perimeters. Tent caterpillar and webworm tents can be noted during regular field inspections while monitoring for other pests and during other field activities.  Look for egg masses on twigs or leaves.  Larvae are most easily identified in the spring.

There are many beneficial insects that will attack these caterpillars; these include stink bugs, assassin bugs, and ground beetles as well as spiders. Several bird species such as chickadees, warblers and woodpeckers also predate heavily on the spring feeding caterpillars. Monitor not only for the pests but for the beneficial organisms as well.

 

Tent Caterpillar

 

Thresholds and Management

Tent caterpillar and webworm tents do not require insecticide treatment. They are rarely of economic concern.

The easiest, quickest most cost effective solution is to prune out the branches and twigs with egg masses on them during the dormant season. If some egg masses are missed then prune and destroy the tents containing the caterpillars when the tents are still small. Dormant oil sprays applied from January until the middle of February will kill the eggs as well. Insecticide sprays applied to control other pests will control young tent caterpillars. Fall webworm usually appears after harvest so control isn’t necessary unless populations are high; spot treatments of infested bushes are effective. To conserve and encourage natural enemies, apply insecticides only if the action threshold is reached and then select the most benign and narrow spectrum materials available.

 

Resources

WSU Extension, Gardening in Western Washington, Tent Caterpillar
http://gardening.wsu.edu/library/inse003/inse003.htm

WSU Whatcom County Extension, Western Tent Caterpillar Update
http://whatcom.wsu.edu/ag/homehort/pest/tent_caterpillar_biology.htm

Oregon Department of Forestry, Forest Health Note, Western Tent Caterpillar
http://www.oregon.gov/ODF/privateforests/docs/fh/WesternTentCaterpillar.pdf?ga=t

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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu