Caterpillar Cocoons Are Killing My Trees

Identification

• Tent caterpillars come in a number of varieties, but all weave tents and cocoons on trees. The species commonly seen during spring include the Western tent caterpillar, the most damaging of all the tent caterpillars. The Sonoran and Eastern tent caterpillars are usually found on fruit trees. The fall webworm is the most common tent caterpillars seen during the middle of summer, while caterpillars of the tiger moths stay on infested trees through winter. The pine webworms and uglynest caterpillars are among the minor tent-producing caterpillars.

Symptoms

• The tent worm's lifecycle of tent caterpillars starts with the female adult moths laying eggs around the tree stems during summer. Each egg cluster contains 150 to 350 eggs that overwinter on tree. The young larvae hatch during active tree growth in spring. Immediately after hatching, the larvae build tents with their silk and pieces of host tree foliage. The caterpillars leave their tents only to feed. Once mature, the caterpillars spin their white, 1 inch long cocoons.

Damage

• Tent caterpillars are aggressive feeders that start eating tree foliage as soon as they hatch. The pests eat the foliage on the entire branch before moving to the next area. As the pests grow in size and numbers, they congregate in small groups, simultaneously feeding on several branches. On small trees, one tent leads to nearly 20 percent defoliation. Heavy caterpillar infestation entirely defoliates trees. Recurrent presence of the pest year seriously affects tree growth, reduces vigor and lower resistance to secondary diseases and pests. Weaker trees die.

Management

• Manually removing the tents and cocoons as soon as they appear is the best control method. Prune and remove the tree areas with egg masses and destroy them. Other control options include Bacillus thuringiensis, carbaryl, cyfluthrin, permethrin or esfenvalerate. Insecticides are most effective when used on newly hatched caterpillars that have not yet retreated into their protective tents.