Bag Worms Are Killing My Deodar Cedar

Pest Description

• Bagworms are the larvae of a moth native to the United States. Host plants of bagworms include over 100 different plants. Young larvae are tiny, measuring about 2 mm long. The pests have shiny, black backs and amber abdomens. The ¾- to 1-inch-long, mature larvae are dirty gray in color, with dark markings on the head. Females do not have eyes, wings, mouthparts or functional legs. Large larvae crawl to infest nearby host plants.

Symptoms

• The pests get their name from the baglike structures or tents that they weave with their silk and pieces of infested tree foliage. The presence of these bags is a distinct symptom of infestation. The bags are so well camouflaged that their presence is often unnoticed until trees have been seriously damaged. The spindle shaped bags are 1 ½ to 2 inches long and are often assumed to be normal tree structures.

Damage

• Bagworms are foliage eaters and feed for about six weeks. Their bags continue to get larger as the worms grow in size. Younger larvae eat the upper layer or the upper epidermis of foliage, creating holes. Older larvae eat entire needles. Severe infestation can cause heavy defoliation. If not controlled, bagworms can continually infest trees year after year and eventually cause tree death.

Control

• Inspect trees carefully for presence of small, upright bags that look like ice cream cones constructed with tree foliage. Control lighter infestations of bagworms by handpicking the bags from the trees. The best time to do this is before the eggs hatch, in late fall, winter or early spring. Use insecticides on the tree during early June when larvae are less than ½ inch long. Chemicals are most effective on younger larvae. Recommended pesticides include permethrin, cyfluthrin, carbaryl and acephate.