Summertime brings joy to most gardeners — blooming flowers, fresh vegetables, green grass. However, summer-feeding insects can wreak havoc on some of our favorite plants. Bagworms (Thyridopteryx ephemeraeformis) are actively feeding on evergreens in our area at this time. Bagworm larvae hatched at the end of May, a little earlier than in most years. Bagworms are not restricted to the host species on which they began feeding. A notable pest of evergreens such as junipers, arborvitae, spruce, pine, and Eastern red cedar, they also feed on deciduous trees and shrubs such as maples and crabapples. Evergreens may sustain severe damage because leaf loss can cause branch death. Deciduous trees and shrubs that have been infested generally produce a new flush of leaves and survive. As the name implies, bagworm eggs and caterpillars/larvae live in bags festooned with pieces of foliage from the plant. In the fall, winter, and spring, the spindle-shaped bags hang from plants in the manner of Christmas ornaments. Bagworms overwinter as eggs deposited in the bags (female pupal cases). Each female produces 500 to 1,000 eggs in one bag. Generally larvae hatch from eggs between late May and mid-June, depending on environmental conditions. Larvae often drop from the bag on fine one- to three-foot silk strands. The strands, caught by the wind, “balloon” the larvae to various locations on the host plant or as far as hundreds of feet or even miles away. Each young bagworm floats until its silk catches on an object or plant. The first mission of the new larva is to form a bag. The larva remains in its bags as it feeds. This bag will increase in size to accommodate the growing larva. By middle to late August, feeding is complete and bagworms begin to pupate inside the bags. In roughly 7 to 10 days, bagworms change into adults and mate, after which the females lay eggs. Young caterpillars, which are an eighth to a quarter of an inch long, initially cause minimal damage, feeding only on the outer layer of leaves. Older larvae, which measure three-quarters of an inch to one inch long, consume entire needles or leaves. Caterpillars start feeding at the tops of a tree or shrub and progress down the afflicted plant. Caterpillars are best controlled once they have settled down and begun to feed. Feeding begins about two weeks after eggs hatch — this year, in late June. Raymond Cloyd, a University of Illinois entomologist, recommends the use of insecticides — among them Bacillus thuringiensis var. kurstaki (sold as DiPel or Thuricide), cyfluthrin (Tempo), trichlorfon (Dylox), and spinosad (Conserve) — to control bagworms. Insecticide sprays are effective on the young caterpillars. Older ones are difficult to control; and females feed less as they prepare for reproduction. The bacterium 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 quite effective in controlling bagworms. Cyfluthrin and trichlorfon are recommended for larger caterpillars, but, again, thorough coverage is essential. The best and most effective means of controlling bagworms is handpicking and destroying bags from fall through midspring. With the use of this method, overwintering eggs are removed before they hatch.
Jennifer Fishburn is the horticulture-unit educator for the University of Illinois Sangamon-Menard Unit. Reach her at firstname.lastname@example.org.
Butterflies add beauty and surprise to any garden, and with a little attention to detail, you can design butterfly-friendly gardens. If you would like to learn how to attract these “flowers of the air,” plan to attend a presentation at 1 p.m. Tuesday, June 29, or 7 p.m. Thursday, July 1, at the University of Illinois Extension Building at the Illinois State Fairgrounds. Sandy Mason of the University of Illinois Extension Unit will describe the kinds of garden plants that attract butterflies and share information about the butterflies that are common to Illinois. Call 782-4617 to reserve a seat and an information packet. The cost is $2.