Northern corn leaf blight: Risk factors and management
Currently, there are no fungicide thresholds specifically for NCLB management; however, researchers have determined it is important to protect the ear leaf and upper leaves as the plant matures through the reproductive stages of growth. Fungicide thresholds are complicated by the differences among hybrid susceptibility to NCLB, time required for infected corn to reach physiological maturity (i.e. black layer), and most importantly, unpredictability in forecasting the weather. To provide some guideline, consider a fungicide on a susceptible hybrids when there is at least one lesion on 50% of the plants prior to or near VT/R1, AND weather conditions are favor disease development. Such conditions are moderate temperatures (64 to 81°F) with several days of light rain or heavy dew for NCLB. Hot and dry weather will suppress NCLB development.
For those considering a fungicide to manage foliar diseases of corn refer to the fungicide efficacy table (note NCLB is Northern Leaf Blight on table) for fungicide options. Because prices vary due to promotions by agricultural chemical companies, fungicide cost should be considered along with fungicide efficacy. Among the fungicides labeled for corn diseases, strobilurin fungicides (FRAC code 11) are more effective before disease development (early detection), whereas triazoles fungicides (FRAC code 3) are effective before and after disease development. Alternating chemistry (i.e. FRAC codes) from one year to another is recommended to prolong fungicide efficacy and minimize selection of fungicide-resistant corn pathogens. A higher volume of water (5 to 7 gal/ac) will improve coverage needed to protect the ear leaf and adjacent leaves at mid-canopy.