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Bt is a stomach poison that is generally most effective on young, hungry larvae (the juvenile stage of many insects). When the insect eats plant material treated with Bt, its gut is destroyed. The pest stops feeding immediately, though it may be several days before it actually dies of starvation. More than one application may be necessary for pest control.
There are about 35 known strains of Bt. Each has a different range of insects it affects. Be sure to select the proper strain. For example, the Bt strain for caterpillars will not control beetles or vice versa.
Bt products come in spray, dust, granular, or pellet form. Many of them contain actual living organisms, so it is important to follow storage directions given on the label. Protect from high temperatures. If stored at 70° F. to 75° F., Bt powders remain viable for 2 or 3 years.
Use caution when applying Bt. Although Bt is considered virtually nontoxic to humans, susceptible individuals may develop serious allergic reactions if the bacterial spores are inhaled or rubbed into the skin. Therefore, avoid breathing spray mist or dust from various Bt products, and protect your eyes and skin when applying Bt. Carefully read and follow label directions.
For further information have a look at the WSU Spokane County fact sheet, "Bt Products" or contact your local WSU Extension Office.
From The Gardener Vol 6, No.1, Spring 1995.(slightly revised 05/05/05)
