How to Manage Pests
UC Pest Management Guidelines
Scientific names: Western tent caterpillar: Malacosoma californicum
Forest tent caterpillar: Malacosoma disstria
In this Guideline:
Tent caterpillars overwinter in the egg stage;
eggs give rise to caterpillars in spring and early summer. The western tent
caterpillar is hairy and dull yellow brown with a row of blue
spots adjacent to orange spots on top of the body. The forest tent
caterpillar is dusky gray, sparsely hairy, with fine
yellow-brown stripes on the shoulder and side separated by a broad blue lateral
stripe. Its most distinguishing feature is a series of white diamond or
keyhole-shaped spots running along its back. Both caterpillars have one
generation each year.
Damage caused by tent caterpillars may be serious on individual
trees. From April to June western tent caterpillars build large silken tents
over leaves on which they feed. Forest tent caterpillars build mats of webbing
rather than tents. They forage in all directions from these mats but return to
the colony when not feeding. Tent caterpillars do not eat leaf veins.
Populations of tent caterpillars tend to be concentrated in
individual trees scattered throughout the orchard. Treatment is only
occasionally required and can be limited to small areas of the orchard.
Organically Acceptable Methods
Bacillus thuringiensis sprays and pruning out infestations are organically acceptable management
On small trees, cut out and destroy
infested twigs. Spray programs for other insects generally reduce populations.
If insecticide treatments are required, localized treatments on individual
trees and branches are generally all that is necessary. Treat when small
caterpillars are first observed. The addition of a wetting agent to increase
penetration of the webbing by the insecticide enhances control.
||Amount to Use**
materials are listed in order of usefulness in an IPM program, taking into
account efficacy, impact on natural enemies and honey bees, and impact
of the timing on beneficials. When choosing a pesticide, also consider information relating
to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
||BACILLUS THURINGIENSIS spp. KURSTAKI#
||MODE OF ACTION GROUP NUMBER1: 11.B2
||COMMENTS: Most effective on small caterpillars. Does not destroy natural enemies.
||DIAZINON* 50 WP
||MODE OF ACTION GROUP NUMBER1: 1B
||COMMENTS: Avoid drift and runoff into surface waters. Where plums are grown near waterways, do not use diazinon.
UC IPM Pest Management Guidelines: Plum
UC ANR Publication 3462
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Insects and Mites:
R. E. Rice, Kearney Agricultural Center, Parlier
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