In severe infections the ears may be completely consumed by the fungus, leaving light-weight husks cemented to the kernels by mycelia. Although feeding damage by the corn earworm is readily apparent, it is the unseen damage caused by thrips that is indirectly responsible for most of the losses to ear rot in California.
Thrips gain access to the kernels through the silk channel opening soon after pollination.
The fungus is found on all corn tissue, but causes few problems unless tissue is damaged. Ear rot is most common in the Delta and Sacramento Valley. Resistance is found in those hybrids with long husks that tightly enclose the silk channel opening of the ears. Husks that prevent or delay entrance of insects are responsible, in part, for resistance to ear rot. Early plantings usually escape serious injury.