Bt is an acronym that stands for Bacillus thuringiensis. It is a natural bacteria that is often used to control various insects such as caterpillars, mosquitoes and fungus gnats while having almost no effect on other organisms like butterflies, humans, mammals, fish, or plants. When it comes to Bt, there are a couple of key strains gardeners use such as Btk Bacilus thuringiensis kurstaki for controlling caterpillars and Bti Bacilus thuringiensis israelensis for controlling mosquitoes and fungus gnats.

This Btk organism controls the larval stage (caterpillars) of moths and butterflies like the tomato hornworm, cabbage worms, loopers, tent caterpillars before they have the chance to hatch and turn into flying pests. It works by paralyzing their digestive system, effectively starving the caterpillar after a few days.Because it is a natural bacteria, products can be OMRI listed which means it can be used in organic agriculture.

Bt is often found in concentrate products like mosquito dunks, sprays, and powders that are applied directly onto your plants. Like all commercial insecticide products, follow label instructions, mix only as much as you need, and store in a cool, dry place out of direct sunlight. Powdered products generally have a longer shelf life than liquids. Do not use Btk in standing water and do not use Bti in water reservoirs used for human consumption.

Cover Image by wormwould, used under its Creative Commons license.

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