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Thursday, June 22, 2006 10:48 pm

The return of the bugs

Those pesky Japanese beetles and bagworms are back

A mature Japanese beetle, a grub, and a pupa
Judging from the heat and humidity, the appearance of fresh-picked zucchini on the table, and the arrival of certain insects, summer is here. Imagine my dismay, while eating a freshly picked bowl of raspberries, at finding a Japanese beetle. This year’s invasion by the leaf-devouring, half-inch-long, colorful metallic-green critters with coppery-brown wing covers has begun.
Adult beetles feed on more than 300 species of plants, but they really like linden, birch, willow, apple, and peach trees and rose bushes, grapevines and raspberry canes. The beetles chew the leaf tissue between the veins, leaving a skeletonized leaf, but they also like to eat flowers. Adult beetles, which are most active on warm, sunny days from 9 a.m. to 3 p.m., are attracted to other beetles and damaged leaves, so early control is the key to preventing a heavy infestations. You have a couple of options:  Handpicking adult beetles early in the morning is one method of controlling an infestation. Hold a bucket containing soapy water or rubbing alcohol beneath the infested leaves. Move the plant or poke the beetles, and they will drop to their deaths.  Heavily infested ornamental plants may be sprayed with carbaryl (sold as Sevin), cyfluthrin (sold as Tempo or Bayer Advanced Garden Insect Killer), or another pyrethroid. Always read and follow label directions for the safe use of pesticides. An affected plant may look devastated, but Japanese beetles only rarely kill woody plants. To learn more about these insects, visit the University of Illinois Japanese beetle fact sheet, located at www.ipm.uiuc.edu/hyg/insects/japanese_beetles/index.html Right now bagworms, whose larvae hatched at the end of May, are feeding on evergreens in our area. These are a most notable pest of evergreens such as junipers, arborvitae, spruce, pine, and eastern red cedar. Evergreens may sustain severe damage because leaf loss can cause branch death. The caterpillars also feed on deciduous trees and shrubs such as maples and crabapples. Deciduous trees and shrubs that have been infested generally produce a new flush of leaves and survive. As the name implies, bagworm eggs, caterpillars, and larvae live in bags decorated with pieces of foliage from the plant. In the fall, winter, and spring, the spindle-shaped bags hang from plants like Christmas ornaments. Young caterpillars are an eighth to a quarter of an inch long and initially cause minimal damage, feeding on the outer layer of leaves. Older larvae are three-quarters to an inch long and consume entire needles or leaves. Because caterpillars start feeding at the tops of trees and shrubs, damage progresses down the plant. Caterpillars are best controlled after they have settled down and begun to feed, about two weeks after the eggs hatch. As is the case with beetles, you have the option of handpicking them from the plants or using an insecticide. One application of insecticide during this time provides a high level of control. A second application may be required a week or two later. According to Raymond Cloyd, an entomologist with University of Illinois Extension, insecticides recommended for control of bagworms include the bacterium Bacillus thuringiensis var. kurstaki (sold as Dipel or Thuricide), cyfluthrin (Tempo), trichlorfon (Dylox), and spinosad (Conserve). Insecticide is effective on the young caterpillars. Older ones, in which the bags are at least 3/4 inch long, are difficult to control, and females feed less as they prepare to reproduce. B. thuringiensis is effective on young caterpillars, but the material must be ingested, so thorough coverage of all plant parts is essential. Spinosad works by way of contact and ingestion and is effective in controlling bagworms. Cyfluthrin and trichlorfon are recommended for larger caterpillars, but, again, thorough coverage is essential.  The best and most effective control is handpicking and destruction of bags, fall through midspring, which ensures that overwintering eggs are removed before they hatch. For more information on bagworms and to view photos of them and the damage they cause, go to Kansas State University’s “Home and Horticultural Pests” Web page, www.oznet.ksu.edu/library/ENTML2/MF728.PDF.  
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