Landscape and Nursery - Juniper Webworm

The following is information on juniper webworm. You may be seeing signs of this insect already this spring. Information is from the University of Maryland.

Juniper Webworm, Dichomeris marginella, Family Gelechidae

This caterpillar usually damages Juniperus species, especially J. horizontalis, J. depressa, J. aurea, J. stricta, and J. squamata. The moths laid the eggs on the junipers last summer. The eggs were laid on the leaves near the base of the current season’s growth. The eggs laid in summer are white to yellow and turn red just before hatch. The larvae web together leaves into silken tubes. The larvae put out silk from their mouth to create this webbing. Since the webbing is small and the caterpillars feed in this small webbed space they often go unnoticed. Also, they tend to web the thick inner growth of the juniper making it harder to detect. In the spring when the webbed branches start to turn brown they become noticeable in the landscape. The larvae in the spring produce a lot more webbing and it is much more noticeable. The larvae themselves are buried deep inside the webbing and dead branches.

Monitoring: Look for the larvae and webbing together of juniper branches in April. Larvae will pupate in a month or so and adults will be active in May to June.

Control: In April and May the easiest control is to prune out the infested foliage. In mid to late summer you should examine junipers and look for the young larvae and webbing of the needles. In the late summer or early fall you can apply Conserve to the foliage to kill the caterpillars or the new Acelepryn from Dupont.

Juniper webworm larvae. Photo from the Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station, Bugwood.org.

Juniper webworm. Photo from the Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station, Bugwood.org

Information from the April 17, 2009 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension.