Archive for Thursday, May 14, 2009

Bagworm season approaching fast in N.E. Kansas

May 14, 2009

We have just about reached the time for bagworms to emerge and start feeding on our trees. Most people are familiar with bagworms, and the damage they do to evergreens (and sometimes deciduous trees), but bagworms don’t always get noticed early enough for their control to be feasible. A lot of times, people want to use chemicals late in the summer when they see the bags in the trees, but at that point the damage has been done for the year. By the time you see new bags in a tree, the bagworms are at a stage in their life cycle where chemicals will not harm them.

The bags you currently see in trees contain eggs and have been hanging there since last summer. In mid-May, those eggs will begin to hatch and juvenile bagworms will emerge to feed.

You could always hand pick all the bags (before the eggs hatch) from small trees to achieve control of them, but on larger trees that is not always possible, so insecticides may be necessary for ideal control. If you want to control bagworms, you will want to start “scouting” for juveniles (about the size of pencil lead) late this month so you will know when they emerge and start feeding.

Once the worms have emerged, you will need to spray a week or so later, before the worms get too big and are more difficult to kill. By waiting a week, more worms emerge, so more are killed by the application. Most entomologists recommend a dual-application method to get the best control. That means another chemical application is needed three or four weeks after the first one, to control any later-hatching worms.

If the bagworm damage from last year is only minimal, you may be able to get by with a single application of spray in early July. If there is enough foliage to support the feeding until then, you can wait and kill all emerged bagworms with one treatment. At that point, all eggs have hatched, and the largest worms are still small enough to be controlled effectively.

I won’t make any specific recommendations on what chemical is best to use in these situations. I simply recommend going to your local lawn and garden store and asking for chemicals that control bagworms. Usually there are many to choose from, and they will all work if used correctly.

When applying the chemicals, be sure to get complete coverage of the tree, including the inner portions of the foliage. If the bags are mostly on the outside parts of the tree, don’t get fooled into thinking that the worms won’t feed on the inner areas too. Also, as usual, always follow all directions on the label, and be aware of droplet size and chemical drift.

If you have questions about bagworms and/or their control, or any other horticulture or agriculture questions, you can contact me at the Leavenworth County Extension Office on the corner of Hughes and Eisenhower roads in Leavenworth, or call (913) 250-2300. I can also be reached via email at


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