If drought conditions are occurring at the same time, the threshold may be lower. Tillage Several factors influence the potential abundance of this pest. They include the size of the spring influx from the south and the availability of suitable food for the first-generation larvae. If the moths arrive before the emergence of the preferred hosts, alternate host plants will be used. These include volunteer weeds on summer fallow.
Tillage reduces the availability of alternate host plants.
Thus, tillage may reduce the establishment of first-generation larvae. Resistant Cultivars Still at the research stage, new cultivars, resistant to feeding by the larvae, may offer the best hope for long-term control. Cauliflower, with glossy leaf waxes, is one example in the vegetable industry. For canola, work is being carried out with chemicals given off by the plants and affecting feeding and egg-laying behaviour. It may be many years before suitable canola cultivars are developed.