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JUNIPER WEBWORM

James R. Baker, Extension Entomologist Emeritus

CAUTION: This information was developed for North Carolina and may not apply to other areas.
JUNIPER WEBWORM, Dichomeris marginella (Fabricius), Gelechiidae, LEPIDOPTERA
Adult juniper webworms are small, brown moths (5/8 inch long) with white wing margins. They are rarely noticed as they fly only when disturbed. Female moths lay tiny white or pinkish eggs that darken with age. The juniper webworm caterpillar is small (3/4 inch long), whitish or light brown worms with noticeable reddish-brown stripes. The pupa is light to dark reddish brown and is about 1/4 inch long.

BIOLOGY

The juniper webworm was first reported on juniper in Europe in 1775. It also occurs in northern Asia and in the civilized parts of the United States. Irish juniper is the preferred host, although Chinese juniper, red cedar and Juniperus communis varieties aurea, horizontalis, depressa, hibernica, suecia, and squamata meyeri are also infested. Juniperus procumbens and Juniperus squamata are infested only occasionally.

 larvaThe leaf mining by newly hatched larvae is inconsequential. Feeding by larger worms may seriously damage ornamental junipers. Large masses of dead needles appear, and the shrubs look unthrifty. Small shrubs may be completely webbed.

 mass of larvaeJuniper webworms overwinter as partially to nearly grown worms inside webbed masses of foliage. Adult emergence occurs from May to July, peaking in June. Males live about 12 days; females about 14. After mating, females lay 50 to 200 eggs singly in the axil of new needles. About 10 days later, tiny larvae hatch, puncture the leaf and feed as leafminers, causing the leaves to brown. The mined leaf is used as a protective retreat from which the tiny worm emerges to feed on fresh foliage. A tiny, white web is formed around the infested leaf. As the worm grows, the web is expanded to encompass dead leaves. Silken tubes are then constructed in which the worms retreat when not feeding. The worms mature throughout the the summer, fall, and winter. By the following spring, they feed gregariously and form a community web. Considerable amounts of foliage may be spun together, and small trees may be completely webbed. The worms pupate inside whitish silken cases, and new adults appear in about 2 weeks to continue the infestation.

 There is one generation per year. Braconid and ichneumonid wasps parasitize the larval and pupal stages of juniper webworms.

Pesticide (Trade Name)
Formulation and Amount
acephate (Orthene)       75% soluble powder: 1/3 to 2/3 pound per 100   gallons of water (homeowner formulations are available)
*azadirachtin (BioNeem, Margosan-O) 0.3% emulsifiable concentrate: 2 1/2 to 5 teaspoons per gallon of water
azadirachtin (Azatin) 3% emulsifiable concentrate: 1/2 teaspoon per  gallon of water
bifenthrin (Talstar) 10% Wettable powder: 1 to 1.5 teaspoons per  gallon of water
*carbaryl (Sevin) 50% wettable powder: 1 tablespoon per gallon of water
cyfluthrin (Decathlon, *others) 20% wettable powder: 1/4 teaspoon per gallon of water (homeowner garden formulations are available)
fluvalinate (Mavrik)  23% flowable: 1/6 to 1/3 teaspoon per gallon of water
*pyrethrins (Pyrenone, others) 6% emulsifiable concentrate: 1/8 to 1 1/2  teaspoons per gallon of water
trichlorfon (Dylox, Proxol) 40% emulsifiable concentrate: 2 to 3 pints per 100 gallons of water


* Suitable for home use.
See the NC Pesticide Manual for other choices.

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact an agent of the North Carolina Cooperative Extension Service in your county.

© 2001 NC Cooperative Extension Service

Prepared by: James R. Baker, Extension Entomologist
Photos from Conn. Agr. Stat. Archives

 ENT/ort-14  July 1994 (Revised)

Web page last reviewed January, 2011 by the webperson.