Time of application and winter wheat genotype affect production of large seed after fungicide application

Two field experiments were established to compare four times of fungicide application (flag leaf emergence, boot, fully headed, and milky ripe) for improving production of large seed. Quadratic models fit the data when large-seed (≥0.238-cm diameter) yields were regressed against time of fungicide application. The optimum time to apply foliar fungicides was between boot and fully headed. Four other field experiments were established to compare large-seed yields after fungicide application on 12 cultivars differing in susceptibility to foliar diseases. With moderate foliar disease pressure, linear models fit the data when increases in large seed due to fungicide were regressed against Kansas Cooperative Extension Service disease ratings. In conjunction with the expected price of seed wheat, these models can be used to help decide whether foliar fungicide is warranted.