Early development of gray leaf spot (GLS) and northern corn leaf blight (NCLB) had us all concerned about the potential for major epidemics of these diseases in 2015. However, conditions have since been warm and dry across most of the state, drastically reducing the spread of these and other foliar diseases. In fact, lesions of GLS and eye spot from early outbreaks can still be found on leaves below the ear in some fields, but in most cases they are of restricted development and the disease has not spread to the upper leaves. Even NCLB, a disease known to affect the upper leaves during the last two months of the season, appears to be low in 2015.
Typical lesions of GLS are rectangular in shape and are clearly delimited by the leaf veins. Under warm, humid or wet conditions, they expand fairly rapidly and produce large amounts of spores that are either wind- or rain-disseminated to new leaves, causing the disease to increase in space and time. This usually leads to epidemics. However, when conditions are as dry as they have been over the past several weeks, lesions either take longer to expand or fail to expand in the typical manner, causing the disease to take on a slightly different appearance. Instead of the typical rectangular shape, GLS may appear as somewhat irregularly-shaped lesions of restricted growth, with yellow halo. These restricted lesions usually produce fewer spores, which reduces the overall spread and development of the disease.