The relationship of gin date to aflatoxin contamination of cottonseed in Arizona

During 1995 and 1996, a commercial gin in western Arizona ginned seed cotton on a field-by-field basis. Seed from each field was kept separate until sampled and analyzed for aflatoxin content according to Arizona Commercial Feed Law. This gave a comprehensive view of field-to-field variability in aflatoxin content as the season progressed. Regression analysis indicated significant relationships between gin date and aflatoxin content in both years: aflatoxin increased with later ginnning. Overall, 89 and 79% of seed lots exceeded 20 ppb in 1995 and 1996, respectively. No field ginned after Julian Day (JD) 273 in 1995 or after JD 267 in 1996 had an aflatoxin content <20 ppb. Means separation confirmed later ginned crops bad significantly greater aflatoxin content (P = 0.05). In 1996, transgenic Bt and non-Bt cottonseed were similarly contaminated. Mean aflatoxin content of Bt cottonseed in 1996 was 413 ppb and that of non-Br cottonseed was 598 ppb. These observations suggest that, in Arizona, losses from aflatoxin contamination of cottonseed can be reduced by early harvest.