Saturday, April 5, 2008

Nursery and Landscape - Juniper Webworm

Juniper webworm can be found on several species of junipers now in the landscape in Delaware. The following is information about this pest.

Photos From the Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station,

The juniper webworm is now being found investing numerous juniper species in Delaware. 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.

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 after pupation to continue the infestation.

The larvae actively feed from March through late April. Pupation occurs on the plant and adults will start to appear sometime in May to June. Examine the inner foliage of junipers for caterpillars and webbing. You may occasionally find them on Alberta spruce too.

Spinosad (Conserve) works very effectively in controlling the larvae of this Lepidopterous pest. Be sure to get coverage of the inner plant where the caterpillars feed. Other materials that are effective include acephate (Orthene), azadirachtin (BioNeem, Margosan-O, Azatin), bifenthrin (Talstar), carbaryl (Sevin), cyfluthrin (Decathlon, others), fluvalinate (Mavrik), and pyrethrins (Pyrenone, others).

Information from the April 4, 2008 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension and from the Juniper Webworm factsheet by James R. Baker, Extension Entomologist Emeritus, North Carolina State University

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