We are already seeing Northern Corn Leaf Blight (NCLB) in some Ohio corn fields. Why are we seeing NCLB this early and how will this affect our yields? For this disease to develop this early, three basic conditions must be satisfied: 1) the fungus (Exserohilum turcicum) must be present; 2) the hybrid planted must be very susceptible to the prevalent races of the fungus; 3) and environmental conditions must be highly favorable.
In fields with early NCLB, the symptoms are very characteristic of a susceptible reaction to the disease, with one-to-six inch long cigar-shaped gray-green to tan-colored lesions on the leaves. This suggests that those fields were indeed planted with susceptible hybrids. Since NCLB develops best at temperatures between 66 and 80 F, accompanied by extended periods of wetness, recent moderate temperatures and frequent rainfall have certainly favored infection and disease development. In addition, the NCLB fungus is always present because it survives in crop residue in the field, and this season the spore load is likely much higher since we had fairly high levels of the disease towards the end of last season. In fact several of the affected fields are no-till, with corn planted into or next to fields with corn stubble.
This may be the perfect storm. Spore build-up + susceptible hybrid + extended periods of favorable weather conditions usually = major disease problems.So, unless, the weather becomes unfavorable over the next few weeks, this disease will continue to spread in fields planted with susceptible hybrids and will likely damage the upper leaves well before grain fill is complete. This would lead to substantial yield loss. When NCLB become established before silking, losses may be as high as 50% if favorable conditions persist. Continue to monitor the progress of the disease and the weather over the next 7 to 10 days and be prepared to treat susceptible fields with a fungicide in order to prevent the disease from spreading to the early leaf and leaves above the ear.