Aflatoxin contamination can be divided into two distinct phases with infection of the developing crop in the first phase and increases in contamination after maturation in the second phase.  Although episodes of contamination are often attributed to one phase or the other (e.g. due to poor postharvest handling or associated with insect damage in the field), both phases contribute to many contamination events. Weather influences the two phases of contamination differently.

Industry observations and those from our laboratory indicate that in warm production areas, the second phase of contamination is frequently the most important. This holds true for both corn and cotton.

Figure Right: In warm production areas, rain on mature crops increases both the quantity of aflatoxin in the harvested seed and the percent of seed lots with unacceptable contamination.