Jaime Cummings, NYS IPM Program
Many of us are familiar with Anthracnose leaf blight and Anthracnose stalk rot, but many of us were caught off guard this year by another form of disease, Anthracnose top dieback, caused by the same fungal pathogen Colletotrichum graminicola. Reports of this disease have been received from all parts of the state in the past week. It affects silage and grain hybrids and is readily identified by its typical symptoms of death of leaves and stalks in the upper 1/3 of the canopy (Fig. 1). It’s important to note that top leaves my die from a number of factors, including corn borer, drought and other environmental stresses. Therefore, accurate diagnosis is important when suspecting this disease. Symptoms initially involve purpling or yellowing of flag leaves, and is often more randomly distributed in a field than top dieback caused by abiotic stresses. Anthracnose top dieback is the result of the fungal stalk rot occurring on upper internodes, which restricts upward movement of water and nutrients, thus resulting in necrosis of leaves, tassels and stalks above the point of infection. The easiest way to identify Anthracnose stalk rot and top dieback is to look for signs of the fungal pathogen. Examine stalks for the typical black anthracnose lesions on the stalks, and peel back the leaf sheath to look for the black fungal fruiting bodies, called acervuli (Fig. 2). A hand lens is helpful in identifying these spiny fruiting bodies, which may be full of pinkish, wet spore masses under moist conditions (Fig. 3). Split stalks will reveal rotten or disintegrated pith tissue at the point of infection (Fig. 4).
This pathogen overwinters in corn residues and spores are transmitted via wind and rain and can infect corn plant roots or stalks. Insect feeding damage may enhance infection by this pathogen. Since this pathogen is more prevalent in fields with high corn residues, crop rotations can significantly reduce this disease. Hybrid resistance is available for anthracnose stalk rot, and hybrids with good foliar disease resistance often reduce stress overall, resulting in less susceptibility to stalk rots in general. The IPM approach to managing anthracnose top dieback in your fields would involve crop rotations, planting resistant hybrids, and cultural practices to ensure minimal plant stress (balanced fertilization, adequate plant populations, and proper drainage).