The 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.
Juniper 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.
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.