Ear and kernel rots of corn
Corn harvest is beginning or rapidly approaching in many parts of Missouri and surrounding states. So far, we have received only a few samples with ear and kernel rots. Usually Diplodia ear rot, Gibb ear rot, Penicillium ear rot and Aspergillus species other than Aspergillus flavus are associated with wet conditions, especially wet falls and harvests that are delayed by wet conditions. Although much of the state has been unusually dry recently, there have already been fields in which these ear and kernel rots are present. In some cases the ears showing molds had been damaged by insects or hail and the molds had come in around the damaged areas. But in other cases Penicillium and Fusarium are showing up on the tips of the ears. And then in fields in which hot, dry conditions occurred at or just after pollination, Aspergillus flavus and aflatoxin could be problems.
Diplodia ear rot, Penicillium ear rot and Gibb ear rot are common problems year in and year out but the severity varies with weather conditions at pollination or close to harvest. The Penicillium ear rot and Gibb ear rot are particularly evident on the exposed tips of ears, around insect tunnels and on ears that have remained upright. If there are periods of wet weather before corn is harvested, some of the corn plants that died prematurely may show the black discoloration caused by secondary fungi coming in on the senescing plant tissues. Because of the wet conditions early in the season, there was a wide range of planting dates for corn. Unfortunately, there were some fields which were silking and pollinating during the stretch of hot, dry weather about mid-season. These fields might be at risk for the occurrence of Aspergillus flavus and aflatoxin.
Both Diplodia maydis and Diplodia macrospora can cause Diplodia ear rot of corn. The ear leaf and husks on the ear may appear prematurely bleached or straw-colored. When the husk is peeled back, dense white to grayish-white mold growth will be matted between the kernels and between the ear and the husks. Small, black fungal fruiting bodies may be scattered on husks or embedded in cob tissues and kernels. The entire ear may be grayish-brown, shrunken, very lightweight and completely rotted. Diplodia ear rot is favored by wet weather just after silking and is more severe when corn is planted following corn.
Penicillium rot is usually evident as discrete tufts or clumps of a blue-green or gray-green mold erupting through the pericarp of individual kernels or on broken kernels. Penicillium appears as small, discrete colonies of mold growth with a dusty or powdery appearance. The fungus may actually invade the kernel giving the embryo a blue discoloration. Blue-eye is the term used for this blue discoloration of the embryo.