The effect of crop rotation, monoculture, and plant stand on the incidence of corn (Zea mays) stalk rot and the associated yield reduction was examined in two field experiments conducted at the Universidade de Passo Fundo during the 1998/99 cropping season. The corn hybrid Pioneer 3071 was sown in four rows (5 m long) per plot. The plots were arranged in a randomized block design with five treatments (30, 40, 50, 60, and 70 thousand plants/ha) and four replications. Stalk rots were assessed weekly from 18 February to 8 April 1999. The disease incidence ranged from zero to 12.9% in the crop rotation area and from 1 to 46.9% under monoculture of corn. Diplodia maydis and D. macrospora were the fungal species most isolated from symptomatic stalks in both monoculture (8.4 and 4.8%) and crop rotation (3.4 and 3.3%) systems.
