UC IPM: UC Management Guidelines for Fall Webworm on Plum

UC Pest Management Guidelines

Plum

Fall Webworm

Scientific name: Hyphantria cunea

(Reviewed 5/06, updated 5/06)

In this Guideline:

Description of the pest
Damage
Management

DESCRIPTION OF THE PEST

Larvae of the fall webworm are pale brown or gray caterpillars with long white hairs arising from black and orange spots. Fall webworms spend the winter as pupae on the tree trunk or ground litter. Moths emerge in late spring and lay eggs on undersides of leaves; eggs hatch in late summer. Larvae feed in webbed colonies on ends of branches. In the lower Sacramento Valley there are two complete generations per year, but in most other sections of the state only one generation occurs.

DAMAGE

From July to September, fall webworm caterpillars are found eating leaves (not veins) and forming silken tents on host trees.

MANAGEMENT

Insecticide sprays applied for other pests often keep these leaf-eating caterpillars in check.

Cultural Control
On small trees, cut out and destroy infested twigs.

Organically Acceptable Methods
Cultural control and Bacillus thuringiensis (Bt) sprays are organically acceptable management methods.

Treatment Decisions
If insecticide treatments are required, localized treatments on individual trees applied when evidence of caterpillars is first observed are generally all that is necessary. The addition of a wetting agent to increase penetration of the webbing by the insecticide enhances control.

Common name

Amount to Use**

P.H.I.+

(trade name)

(conc.)

(dilute)

(days)

The following 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.

BACILLUS THURINGIENSIS ssp. KURSTAKI#

(various products)

Label rates

—

MODE OF ACTION: A microbial (Group 11.B2)¹ insecticide.

COMMENTS: Most effective on small caterpillars. Does not destroy natural enemies.

DIAZINON* 50WP

3 lb

1 lb

DIAZINON* 4EC

3 pt

1 pt

MODE OF ACTION: An organophosphate (Group 1B)¹ insecticide.

COMMENTS: Avoid drift and runoff into surface waters. Where plums are grown near waterways, do not use diazinon.

**	For dilute applications, rate is per 100 gal water to be applied in 300-500 gal water/acre, according to label; for concentrate applications, use 80-100 gal water/acre, or lower if the label allows.
+	Preharvest interval. Do not apply within this many days of harvest.
*	Permit required from county agricultural commissioner for purchase or use.
#	Acceptable for use on organically grown produce.
—	Not recommended or not on label.
¹	Modes of action are important in preventing the development of resistance to pesticides. Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode of action is assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

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 the insects and mites section:
R. E. Rice, Kearney Agricultural Center, Parlier

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