Fertilome Caterpillar Killer with Bt is a biological insecticide for use on fruits, vegetables, shade trees, and ornamentals plants to treat a variety of leaf-feeding worms. Pests treated include bagworms, tent caterpillars, gypsy moths, cabbage loopers, and tomato hornworms. Hi-Yield Thuricide may be applied up to and including the day of harvest.

Bacillus thuringiensis (Bt) is a naturally occurring bacterium found in soils throughout the world. It is unique in that it offers unusual properties that make it useful for pest control, especially the control of leaf-feeding insects. This is because Thuricide reacts with the cells of the stomach lining of target pests, causing them to not be able to feed within hours after contact. The insects eventually die from starvation. The most common strain of Bt is the kurstaki strain which will kill leaf- and needle-feeding insects such as caterpillars and webworms.

Bt is generally considered beneficial in that it is naturally occurring and will not kill other non-target insects. For example, if Bt is applied to a vegetable garden, it will not kill honeybees or other pollinating insects. Also, it breaks down in sunlight within 1-2 weeks.

Bt will kill vegetable, fruit, tree and crop leaf-feeding insects such as the cabbage worm (cabbage looper, imported cabbageworm, diamondback moth, etc.), tomato and tobacco hornworm, European corn borer, Alfalfa caterpillar, alfalfa webworm, Leafroller, Achemon Sphinx, Tent Caterpillar, Fall Webworm, Leafroller, Red-humped caterpillar, Spiny elm caterpillar, western spruce budworm, pine budworm, and pine butterfly.