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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis


Posted by John Fulton -

After some very severe infestations of bagworms the past few years, the calls have been coming in all year on the correct treatment times for bagworms this year. Year-in and year-out, the correct treatment time for bagworms is June 15. You can mark this date on your calendar for

next year and be within a few days of the correct treatment time. With a very cool spring, a week later may be a possibility. The opposite is true for a very warm spring. The idea is to have all the eggs hatched before treatment, but not wait until the bagworms are almost mature.

The next problem is what to use. The traditional standby has been Sevin, but the B.t. products such as Dipel and Thuricide have really taken their share of the market the past several

years. The B.t. products have several good points including safety to mammals and toxicity to larger bagworms. Since they are bacteria that affect only the larvae of moths and

butterflies, it does take a while for the bacteria to build up to the point where they can kill the bagworm. I won't get into the discussion about Monarch butterflies lighting in the tree just after treatment (actually these products don't kill the butterflies – only the larvae would be killed).

If you are in doubt about whether you have bagworms, check your trees and shrubs around June 15. You can actually see the small bags as the larvae build them. They become very noticeable at about 1/16 of an inch long. Treat bagworms early, since larger ones are more difficult to control. The spring we have had is probably going to zero out the timing, meaning the last two weeks of June should be ideal.

Most people think that bagworms only affect evergreens. True, that is their preferred host group, but bagworms have a huge number of potential hosts. Through the years I have seen them on oak trees, grape vines, apples, and about any other growing thing you can think of. Make sure to check the tops of tall trees. An infestation may get started in a tall tree simply because you can't reach the top when applying a control. In that case, you'll have to use a taller ladder.

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