For Release June 6, 2004

It's Time To Control Bagworms

by Chuck Otte, Geary County Extension Agent

Bagworms, the scourge of junipers and cedars, are getting active again, so now is the time to start monitoring and controlling these annual pests. Adult bagworms are a moth. Few people know that because the adults are rarely seen. Late last summer the adults emerged. The females have no wings so depend on pheremones they release to attract male bagworm moths to mate with them. After mating she crawls back into the bag she just emerged from and proceeds to fill it with up to a thousand eggs. And then see dies.

Those eggs spent the winter nestled in that old bagworm case just waiting for spring and warm weather to return. By mid May the eggs were hatching and I was finding tiny little bagworms crawling around starting to feed already. Not all the eggs hatch at the same time. The cumulative hatch occurs over a several week period that has pretty well wrapped up by now.

Early in their life, small bagworms don't eat a lot. They spend time making their little mobile home and decorating it with bits of foliage off the host plant, and of course, eating. Bagworms can live on almost any plant that has leaves. The list of host plants is over 200 species long. But they are the most damaging on junipers (cedars), arborvitae and spruces. These plants can only grow from the branch tips out. Once they are defoliated, they will die. Deciduous tree and shrub species may also be defoliated, but they can generate new leaf buds and survive.

Over the next four to six weeks, many homeowners will not even notice that they have a problem. But by early July the bagworms increase their size and their appetite. It may seem that the problem developed overnight, but the bagworms had been present for weeks. They will only leave the plant that held their egg case if they run out of food.

Early detection and awareness of a bagworm problem leads to more control options, easier control options and less damage to the host plant. If you or your neighbors had bagworm problems last year, then you will probably be faced with bagworm problems this year as well, even if you did treat last year. Get out there and start looking for those small bagworm bags which may only be a quarter of an inch long at this time.

The biological control Bacillus thuringiensis, or Bt, can be very effective, but you need to start control measures early as it is far more effective against small bagworms than large ones. Make three to four applications of Bt about ten days apart. Thorough coverage of all foliage is critical with Bt, or any control measure, so I encourage use of an applicator that attaches to the end of a garden hose to apply a thorough soaking spray.

For chemical control measures, many products are registered and very effective including: acephate (Orthene), carbaryl (Sevin), cyfluthrin, fluvalinate, malathion and permethrin. These active ingredients are found in many products, so check the label to see if it contains any of these chemicals or if it mentions bagworms under insects controlled. Be sure to follow label directions for mixing rates and safe use statements. Remember to use a hose end sprayer and apply two to three doses ten to fourteen days apart.

Bagworms can be devastating. If left unchecked they will kill junipers and spruces. Early detection and early treatment are necessary to minimize damage.


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