The timing of the ashfall will affect the chances of survival of grain and cereal crops. For example, when corn is in a vegetative period during the first two months of growth, light ashfalls are unlikely to affect the expected yield. Heavy ashfalls, however, bury much of the plant and change the soil characteristics sufficiently to result in crop failure. The most critical period for corn yields is between three weeks before tasselling to two weeks after pollination. Even light ashfalls during this period could result in barren stalks and crop failure. Damaged stalks are also more susceptible to disease, which may also reduce yields.
Corn requires many heat units for a crop to reach maturity. An eruption could delay crop maturity if sunshine hours were reduced during the eruptive period. Ashfall near crop maturity will make harvesting difficult and reduce the quality of grain. Ash collected within and among the spikes will cause some contamination of the harvested grain. A high proportion of ash will be removed in the cleaning procedures already used in flour mills if ashfalls are light.