Lawn & Garden Care | Bag Worms

ifr150612–81
Lawn & Garden Care | Bag Worms
Phil Nixon, Extension Entomologist - University of Illinois

Depending on exactly where you live in Illinois it may be time to treat for bag worms on your trees and shrubs. Todd Gleason has more from University of Illinois Extension.

Bag worms are caterpillars that commonly live in groups…
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Bag worms are caterpillars that commonly live in groups. These groups are not colonies, the worms just live near each other. Honestly, bag worms live in little silk tents. They haul these tents, bags, around with them. The tents are camouflaged with pieces of leaves says University of Illinois Extension Entomologist Phil Nixon.

Nixon :31 …but also will get on deciduous trees.

Quote Summary - Being detached pieces of foliage these will dry up and turn brown. Bag worms are problem primarily on needled evergreen trees; junipers including eastern red cedar, arborvitae, and eastern white pine. Bag worms are found almost exclusively on the white pine in the northern half of the state. In the southern half of Illinois it lives on those plants and deciduous trees.

It is very common to find bag worms on oak trees, maple trees and crabapples in the southern half of Illinois. Bag worms are easy to spot.

Nixon :26 …in a controllable state with an insecticide.

Quote Summary - What you see is a spindle shaped bag up to an inch-and-a-half long that is dark in color. An actively feeding bag worm is always getting large and is always putting new foliage at the top of the bag. So, if it is actively feeding the caterpillar will always have green foliage at the top of the bag. This one way to tell if it is in a controllable state with an insecticide.

Bag worms start at the top of the trees and work done. They strip the leaves as they go. Normally this kills the parts of the tree that have had the leaves, the needles, eaten away. It is best to treat for bag worms in June and July says Nixon.

Nixon :23 … all brown after about a week.

Quote Summary - We look at controlling these insects through applications of Bacillus thuringiensis kurstaki sold as Dipel, Thuricide and other brand names. When ingested by the caterpillar is will kill the caterpillar. You’ll know they are all dead because the tops of the bags will be all brown after about a week.

The older the caterpillar is the harder it will be to kill. Bag worms stop feeding in August and essentially their tent becomes a cocoon. Treating then won’t do any good. The bag will already be all brown because the caterpillar has stopped feeding.