Monitor the crop once per week by inspecting randomly selected plants throughout the paddock. Record pest numbers and their development stages. Use these counts to judge whether a spray is required and to check whether control tactics applied previously have been successful. The more plants you look at, the more accurate will be the assessment of what is happening in the crop. Bt is a bacterium that is formulated into a biological insecticide.
Bt products registered for use on Brassica crops kill only caterpillars.
Ensure good spray coverage of the plant, as the pest must eat Bt for it to be effective. Do not expect instant knockdown. Apply Bt after irrigation, not before. A central feature of this strategy is separation of the calendar year into two windows, with the use of each new chemical being restricted to one window. The strategy aims to delay the development of resistance to new insecticide groups.