Expert: Jim Hyland - 8/8/2006

Question
Location is in Southern Illinois near Mt. Vernon. Problem is bagworms on cypress and other evergreens. Will spraying at this time of year have any impact for this year or next? What impact would spraying in the fall months have if any and which would be the best months? hen is the best time in spring? Will soap based insecticides such as Safex from Lowes work?

Answer
If only a few small trees or shrubs are infested, picking the bags off by hand and disposing of them may afford satisfactory control. This approach is most effective during fall, winter or early spring before the eggs have hatched.

When many small bagworms are infesting evergreens, an insecticide may be needed to prevent serious damage. The best time to apply an insecticide is while the larvae are still small (less than 1/2-inch long). In Kentucky, this is usually in June. Small larvae are more vulnerable to insecticides, and inflict less damage. Carefully inspect susceptible landscape plants, especially evergreens, for last year’s bags. Young bagworms are harder to see; look closely for the small, upright bags which have the appearance of tiny ice cream cones constructed of bits of plant material. Preventive treatment is often justified on plants that were heavily infested with bagworms the previous year.

Several products are available for homeowner and professional use. For homeowners, conventional insecticides such as Sevin, Dursban, diazinon, and malathion, or the microbial insecticide Bacillus thuringiensis (BT) provide satisfactory results. The BT products have very low mammalian toxicities, but are only effective against younger larvae. If large bagworms are present (more than about 3/4-inch long), a conventional insecticide probably will provide better results. For nursery and landscape professionals, other effective products include Astro, Decathlon, Ficam, Mavrik, Orthene, Pounce, Scimitar, Talstar and Tempo. Foliage should be throughly wetted with the insecticide spray in order to achieve thorough coverage.
I do not think that Safer Insecticidal Soap Concentrate will have any affect on the bagworms. Insecticidal soaps are used for mostly soft bodied insects as a contact spray. bagworms are so protected by the bag it will not work. I checked the label of  Safer Insecticidal Soap Concentrate and it does not list bagworms as one of the insects it will control.