Bacillus thuringiensis kurstaki (makes 100L)

Bacillus thuringiensis kurstaki (makes 100 litres)

Bacillus thuringiensis kurstaki (Btk) is a soil bacterium whose crystal proteins kill caterpillars that eat a sprayed leaf. One vial makes 100 litres of foliar spray for caterpillars, cutworms and other leaf eating larvae.

At a glance

• Type: biological insecticide (Bacillus thuringiensis kurstaki)
• Analysis: 9.2 × 10⁸ CFU (supplier figure)
• Use for: foliar spray against caterpillars, cutworms and other soft bodied caterpillar species
• Rate: 0.4 g per 5 litres of water; one vial in 100 litres, or one tenth of a vial in 10 litres

What it is

Bacillus thuringiensis (Bt) is a group of naturally occurring soil bacteria. As they form spores they also make crystal (Cry) proteins. The kurstaki strain makes Cry proteins that act in the gut of caterpillars, the larvae of moths and butterflies, and on little else.

What it does

• A caterpillar has to eat a sprayed leaf. The Cry protein damages its gut lining, it stops feeding within hours and dies over the following days.
• It does not kill on contact, and it does not act on aphids, mites, thrips or other sucking insects.
• It does nothing to the plant, so it can be used on edible crops close to harvest.

How to use

• 0.4 g per 5 litres of water. Shake until dissolved.
• Mix the whole vial with 100 litres of water, or one tenth of the vial with 10 litres, and spray the affected areas.
• Cover both sides of the leaves. The caterpillar has to eat the spray, so coverage matters more than dose.
• Growers spray late in the day, because sunlight breaks the protein down, and spray again after rain or as new leaves grow.

Handling and storage

• Keep the vial sealed and dry until you mix it.
• Wear gloves and wash hands after use.
• It kills any caterpillar that eats it, including the ones you want. Keep it off swan plants and any plant you are growing for butterflies.
• It works slowly. Feeding stops first; dead caterpillars follow over a few days.