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Bagworms becoming active in the landscapeQ: What do some Oklahoma landscape pests and government employees have in common? A: They never miss their holidays. All joking aside, holidays are a great way to remember garden chores. Webworms are on Memorial Day and Labor Day, cedar apple rust galls can be found at Christmas, onions are planted on Valentine's Day and potatoes are planted on St. Patrick's Day. The pest to be on the look-out for around Memorial Day is the bagworm. Bagworms can be serious pests in the landscape if left untreated. In Oklahoma the most common hosts are eastern red cedar, other junipers, and arborvitae. Other hosts sometimes damaged include pines, spruce, bald cypress, maple, boxelder, sycamore, willow, black locust, oaks, and roses. The bagworm has been recorded on 128 different plant species in various parts of the United States. Bagworm larvae damage their hosts by feeding on the foliage. Heavy infestations can completely defoliate small plants. Defoliation usually kills hosts such as red cedar and other junipers. Broadleaf hosts are not killed but are weakened and become more susceptible to borers and diseases. The overwintered eggs (in the year old female bags) begin to hatch in late April or early May and the young larvae begin to feed and construct bags immediately. The first evidence of an infestation is normally a small bag, about 1/4-inch long, standing almost on end. As larvae grow, silk and fragments of the host plant foliage are added to the bag until it reaches 1 1/2- or 2-inches long. When larvae are mature they fasten the bag to a plant stem with silk. Pupation occurs in the bag in August and males emerge in late August and September. They engage in a mating flight in search of the wingless females still inside their bags. After mating the female lays several hundred white eggs inside her old pupal case, drops from the bag, and dies. There is one generation per year. Adult males are small, clear winged moths with a black, hairy body and a wingspread of about 1 inch. Adult females are wingless, have no functional legs, eyes, or antennae, and are almost maggot-like in appearance. Talk about getting the short end of the stick, no wonder she never leaves the bag. The female body is soft, yellowish white, and practically naked except for a circle of woolly hairs at the posterior end of the abdomen. Mature larvae have a dark brown abdomen and the head and thorax are white, spotted with black. They are about 1-inch long. Both larvae and adult females are found in silken bags on the host plants. The good news about these damaging pests is that they are easy to control. Easy to control that is if measures are taken at the appropriate time. If scouting is done and immatures are spotted treatment should be taken. A product containing Bacillus thuringiensis var. kurstaki can be applied to the plant. Bt is a bacterial insecticide that is pest specific. This is a benefit because it will target the bagworm and not affect any other beneficial insects that might be found on the plant. Bt var. israliensis is another variety that is commonly used to control mosquito larvae. When purchasing Bt, check the active ingredient list to assure that the product will be effective on bagworms. If the plant is fairly small it is possible to hand pick the bags off of the plant. But a very thorough inspection must be done, because even if one is left on the tree the eggs can hatch and a problem can erupt. Hand picking should have been done early in the year. By now the immatures are on the move and removing the bags will be wasted time. For more details about scouting for bagworms contact the OSU Master Gardeners at 405-713-1125. 6/2/08 Date: 5/23/08
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