We had the first reports of bagworms hatching in Maryland last week. Check your plants for egg hatch before treating them with an insecticide. If you see small caterpillars present, you can apply a pesticide containing Bacillus thuringiensis (Bt) to control them. Read and follow the product label instructions. https://extension.umd.edu/resource/bagworms-trees-and-shrubs

Christa

I am sorry that caused confusion. The biological insecticide, Bacillus thuringiensis has the lowest impact on beneficial insects and it is most effective when the bagworm caterpillars have just hatched and are very small, no more than about 2/3" in length. So, the best timing is when you see them hatch and they are small (early June up to mid-July or so). Once the caterpillars are larger and 2/3", then a stronger insecticide is needed. We recommend spinosad as the next step up for treatment. The best way really is to monitor the bagworms and go by their size, rather than by the calendar dates, as they are approximations and can vary by temperature differences from year to year.

This is a very good article on bagworms from Ohio State University that just came out today and shows what the young caterpillars look like, and provides further details about managing them.

https://bygl.osu.edu/index.php/node/1795

Christa