The inoculum quantification of Diplodia macrospora and D. maydis is important for a better understanding of the role of plant debris as source of inoculum for corn (Zea mays) ear rots and for developing alternative control strategies for these diseases. Field trials carried out during the summer crops of 1995/96 and 1996/97, quantified the amount of plant debris remaining on the soil surface after harvest, the number of conidia on such debris, and the airborne inoculum of D. macrospora and D. maydis were quantified. The incidence of each fungus species in the harvested grains was also determined. The conidium number in plant debris was higher in D. macrospora (2,1 x 10(5) m-2) than in D. maydis (1,0 x 10(5) m-2) in 1995/96 but lower in 1996/97 (4,2 x 10(5) vs. 3,4 x 10(6) m-2). While the airborne inoculum of D. maydis increased from planting to the fourth week, conidia of D. macrospora were more numerous from the tenth week to harvest. The average incidence of each fungus species in grains was 74% in D. macrospora and 26% in D. maydis. These results showed the relative importance of each fungus species in the infection of corn ears and grains. The plant debris remaining on the soil surface was shown to be essential to survival and infection of corn plants and ears by these pathogens.
