Survival of Stenocarpella maydis on corn residue in Indiana

Diplodia ear rot (DER), caused by the fungus Stenocarpella maydis, has become a prevalent corn disease in the Midwest. The survival of S.maydis on corn kernels and stalkswas evaluated in Tippecanoe, Co., Indiana, over 17 months. Infested corn residue was either left on the soil surface or buried at 10 or 20 cm. Survival of S. maydis was determined by observing the presence of pycnidia per unit of corn residue under a stereomicroscope and by assessing conidia viability by evaluating germination. Months of environmental exposure and soil depth affected S. maydis survival. Pycnidia production and conidia germination were observed up to 11 months on corn kernels and 17 months on corn stalks when left on the soil surface. Minimal or no conidia germination of S. maydis was observed on residue recovered from 10 or 20 cm after 4 months on kernels and 7 months on stalks. These results demonstrate that surface corn residue can be a long-termsource of inoculum and at least two years of rotation to a nonhost crop or residue removal through tillage may be necessary to reduce potential initial inoculum.