Juniper (Juniperus)-Juniper webworm

Dichomeris marginella

Pest description and damage The adult juniper webworm is a copper-brown moth with white bands on the edges of the front wings. The moth is about 0.5 inch across. The mature larva is a yellowish to brownish caterpillar, 0.05 to 0.06 inch in length, with dark brown lines on the back and a dark head. The webworm caterpillars initially feed by mining inside leaves, then gather to feed in small colonies or nests of webbed foliage as they mature. Due to their habit of feeding deep in the plant canopy, damage is overlooked. Damaged foliage turns brown and is covered with dirty webbing. Considerable amounts of foliage are spun together, and small trees may be completely webbed. Frequently, damage is observed in early spring from March to May. This pest infests only juniper.

Biology and life history The caterpillars overwinter in the nest, which consists of webbed twigs, as well as silk tubes through which the caterpillars move through the juniper foliage and webbing. These larvae resume feeding in spring then pupate. Adult moths fly in late spring. Eggs are laid on leaves of the current season's growth. Larvae feed first as leafminers, then feed on the surface of leaves while building silken tubes around the feeding site. They overwinter in small groups in these webbed sites. There is one generation per year.

Pest monitoring Watch for the first signs of webbing.

Management-cultural control

Hand-pick caterpillars and prune out infested growth. Irish juniper (J. chinensis 'Stricta') is the preferred host, although Chinese juniper, red cedar, and Juniperus communis varieties aurea, horizontalis, depressa, hibernica, suecia, and J. squamata 'Meyeri' are infested. Juniperus procumbens and J. squamata are infested only occasionally.

Management-chemical control

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For more information

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