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Tips to prevent bagworm infestation

Q: I had those bagworms that hang at the end of the branches last year. Is there anything I can do to prevent them this year?

A: This is the PERFECT time to ask about the dreaded bagworm.

The little black crawlers that make the pine cone-like bags on evergreen trees and shrubs and feed on new growth of the host plants have begun to hatch here in the Mahoning Valley.

Some of these little black crawlers will re-inhabit any bags that were not removed last season. The bag I am referring to looks like a small pine cone hanging from the branch, as the insect uses material from the host tree or shrub to construct this safe haven.

The eggs overwintered inside the mummified female, which is inside last season’s bag. The small, blackish larvae exit the bottom of the bag and spin down on a strand of silk. These “larvae on a string” get picked up by the wind and “balloon” to a suitable host where they begin to feed and build a new bag using bits and pieces of the host plant.

In the coming days, they are barely noticeable. The tiny brown bag is only an eighth of an inch long and may be passed over as a seed or something you think has fallen from another tree.

Bagworms can build up heavy local populations on preferred hosts, especially arborvitae, cedar and juniper. If crowded, they may eat buds on these plants, causing branch dieback, and open, dead areas. If defoliation is excessive, plants may die the following season. Bagworms also attack numerous deciduous plants, although injury is not nearly as severe as on evergreens.

The chewing mouthparts of bagworms can decimate small trees and shrubs, but to conifers it can be the most devastating. I saw a juniper recently that had been completely defoliated. These insects first eat the new tender leaves and needles, then they graduate to the tougher vascular tissue. The danger with evergreens is being completely defoliated, as they have needles that stay on the tree for three-plus years. Thus, they can be stripped of several years’ growth and the tree or shrub may not recover.

Keep an eye out for this pest, especially if you had problems last season. If there are just a few bagworms on a plant, handpick and destroy them. You can crush them on the ground or put them in a plastic bag and toss them in the trash. This is the most effective control that any homeowner can do.

It’s easy and it provides a little exercise. Pluck the bags you can reach. Using a ladder can be dangerous when moving limbs around while on uneven ground.

For those of you really having challenges with bagworms, Bt is organic and is effective against bagworm when bags are less than 3/8 inch in length. This is only effective for the next couple of weeks while the insect is small.

For more control options, photos and descriptions of this insect, go to http://go.osu.edu/bagworm.

Barrett is the Ohio State University Extension educator for agriculture and natural resources in Mahoning County. Call 330-533-5538 to submit your questions to the plant clinic. Live clinic hours are 10 a.m. to noon Mondays and Thursdays. Or visit go.osu.edu/mahoningclinic.

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