I hate to be the bearer of bad news, but the time for bagworms to emerge and start feeding is almost upon us. Most of us are familiar with bagworms, and the damage they do to evergreens (and sometimes deciduous trees), but they don't always get noticed early enough to control them. A lot of times, people want to take action when they see the bags, but at that point the damage has been done for the year and the only thing to do is hand-pick the bags from the tree.
Right now, the bags you're seeing contain eggs and have been hanging there since last summer. Typically in mid-May, those eggs will hatch and juvenile bagworms will emerge and begin feeding. This year, because of the delayed warm temperatures, the hatch could be delayed until late May or early June. As I said above, you can pick those bags off your tree to get rid of the eggs, but that isn't always feasible on large trees. In most cases chemical control is your only alternative to hand-picking the bags.
You will want to start "scouting" for these small bagworms (about the size of pencil lead) late this month so you will know when they emerge and start feeding. Once you see that they've emerged, you will need to spray a week or so later, before they 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 of bagworms. That means another chemical application will be 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.
This time of year has a lot of insect activity and plant growth, so if you see anything feeding on your plants this spring, or have any other questions about bagworms or other plant pests, don't hesitate to ask me about it. You can stop by the office at 500 Eisenhower Rd., Suite 103 on the corner of Hughes and Eisenhower roads in Leavenworth, or call (913) 250-2300. I can also be reached by email, at "firstname.lastname@example.org".
- Mike Epler is the agriculture agent for Leavenworth County's Kansas State University Extension