Waste Corn as a Point Source of Inoculum for Aspergillus flavus in the Corn Agroecosystem

Sporulation of Aspergillus flavus was detected on kernels in deposits of waste corn close to corn storage cribs and bins at 18 locations throughout Iowa in 1991 and 1992. A. flavus was detected in spore traps located 3 m from the deposits and was isolated from nitidulid beetles within the deposits or in insect traps within 3 m of the deposits. A. flavus also was isolated from asymptomatic corn kernels in the deposits and from soil beneath the deposits. Linear dispersal gradients of airborne conidia of A. flavus, sampled at distances of 2, 6, 10, and 14 m from waste corn deposits into adjacent cornfields, were detected at three sampling times between 28 July and 1 September 1992 at Cedar Rapids and Williamsburg, Iowa. Linear dispersal gradients from the deposits also were detected for A. flavus-infested nitidulid beetle species Carpophilus lugubris and Glischrochilus quadrisignatus. The incidence of A. flavus infection on corn leaves, silks, and kernels in the fields adjacent to the deposits were correlated to numbers of airborne conidia at each sampling time at both locations. In a field experiment in Ames in which waste corn was placed in the center of individual corn plots, linear dispersal of conidia of A. flavus and plant infection gradients similar to those found from natural deposits were detected at distances of 1.7 to 8.5 m from the deposits at four sampling times from 6 August to 26 September 1992. Few airborne conidia of A. flavus were detected, and no infection of leaves, silks, and kernels by A. flavus occurred in the corresponding noninfested control plots. This study showed that deposits of waste corn infested with A. flavus found in the vicinity of corn storage cribs and bins are point sources of inoculum for A. flavus in the corn agroecosystem.