Beating Back Bagworms
By Paul James
Bagworms can be a bummer. Left undetected and uncontrolled, they can quickly defoliate and destroy their host plant, particularly conifers — junipers, pines, spruces, bald cypresses, and the like — and to a lesser degree maples, sycamores, willows, oaks, even roses. And now’s the time to be on the lookout for them.
So what exactly are you looking for? Last year’s “bags” or cocoons, for starters. Bagworms overwinter in their carefully constructed homes, so now’s a good time to inspect plants and remove any leftover bags, because the eggs within them (which can number in the thousands) will soon be hatching and developing into larvae (tiny caterpillars). The larvae then release a thin silk thread and float down out of the bag or are carried by the wind to other plants to begin feeding and creating new bags made of leaves and twigs, all bound together with silk.
The larvae themselves are tiny and hard to see, so look instead for the tiny bags as they begin to form and begin treatment right away.
Two of the best controls — other than handpicking — also happen to be all natural and approved for use by organic gardeners — Bt (Bacillus thuringiensis) and Spinosad. Bt is available as a dust or liquid and should be applied in the early evening or on a cloudy day because it breaks down quickly when exposed to sunlight. Spinosad (such as Captain Jack’s Dead Bug Brew) is also available as a dust or spray.
It may take two or three repeated treatments spaced a week apart to achieve complete control, and both Bt and Spinosad should be reapplied after heavy rains.
So what happens if you don’t get rid of bagworms in spring? Well, their life cycle begins anew in September. Male bagworms — fuzzy black moths with transparent wings that live only one or two days as adults — emerge from their bags in search of a mate, and with no time to spare. Female bagworms — who have no functional eyes, legs, mouthparts, or antennae — spend their entire lives in their bags and ultimately decay into a mass of eggs. Come spring, the eggs hatch into larvae in search of your plants.
Happy gardening, ya’ll.
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