| Bt is Bacillus thuringiensis, a bacterial strain that specifically affects caterpillars. It is considered an organic treatment. It stops infestations by causing young caterpillars to stop feeding, and the caterpillars die of starvation. It works best on smaller, younger caterpillar stages. You can buy Bt as Dipel or any of several other brands (no advertising plug intended). After using Bt, you may still see caterpillars on the plants for a few days. However, if they ingested the Bt, they will stop feeding and eventually curl up and die. They're sick. Bt is a surface treatment, not systemic. It needs to be reapplied after rain or watering, and it does degrade over time with sunlight. It's harmless to pets, people, birds and other nontarget species. Bt is best used when no rain is expected for a few days and if you can water from the bottom or at soil level instead of top-watering. It's good to apply Bt on cloudy days or in the evening, as it's degraded by sunlight. This gives the caterpillars an opportunity to eat the Bt-- they must ingest the bacteria; it's not a contact poison. Make sure that you get Btk, the strain of Bt that gets caterpillars. There are other strains of Bt, such as Bti that kill mosquito larvae or other targets, but Btk is the one for plant-type caterpillars. Note that Bt will also kill "good" butterfly caterpillars so use caution with it around butterfly host plants if you are intentionally raising BF's. Oh, and spinosad also works for pinworms. |
