The ideal time to apply a fungicide to corn to achieve maximum yield response and optimum disease control is the short window between tassel emergence (VT) and blister stage (R2). Though most fungicides applied on tasseled corn include both curative and preventative active ingredients, fungicides are far more effective at preventing disease infection than they are at stopping disease after plants have been infected. Many leaf diseases can take seven to ten days before lesions appear after infection, therefore waiting to see visible signs of disease is not always recommended, especially on disease sensitive hybrids when conditions are favorable for disease infection.
Hybrids that respond positively to fungicide treatment, or historically have been sensitive to disease pressure should be treated shortly after tassel emergence. Hybrids with a low response to fungicide, strong genetics against disease, and/or planted on soybean residue, may need continued evaluation until more disease pressure develops, but treatment before blister stage still provides the best return on investment. If you elect to wait on fungicide treatment, a later treatment will still be effective at stopping disease progression. These later treatments can also improve plant standability at harvest time, but positive yield responses to offset treatment costs will be more difficult to obtain.
Aside from disease prevention and treatment, fungicides also help mitigate plant stress including heat and drought that occurs during pollination through grain fill. Fungicides provide no protection against Goss’s Wilt and Bacterial Leaf Streak infections. However, a fungicide may be recommended to offset the plant stresses these diseases create.
Tassel time fungicide treatments are also a good time for some tank mixing with insecticide for silk and ear damaging pests including Western Bean Cutworm, Rootworm Beetles, and Japanese Beetles. It is not recommended to add insecticide when not needed, so a thorough scouting of a field for these insects before application must be made.