In field and greenhouse investigations an Aspergillus flavus inoculum presented to the involucral nectaries of flowers and developing bolls resulted in significant increases in the number of infected seed. However, the receptivity of flowers and developing bolls changed through the growing season. Peak infection levels generally occurred in bolls set during the early part of the peak flowering period. These are the bolls that mature in August and early September, on the lower third of the plant. It has been reported previously that these bolls generally have the highest aflatoxin levels (1, 2). High aflatoxin at this time may be, in part, a result of the ability of the toxin-forming mold to enter only the early season flowers and developing boils.

Water potential is also an important factor in A. flavus entry into cottonseed. Among flowers inoculated at the involucral nectaries, those on plants with noon water potentials between -16 and -19 bars on the day of inoculation had significantly higher A. flavus contamination levels than those with water potentials outside of this range.