Weather‐Associated Changes in Aflatoxin Contamination of Preharvest Maize

Abstract

Aflatoxin contamination of maize ( Zea mays L.) is a chronic problem in the Southeastern USA, but varies greatly from year to year in its severity. Our primary objective was to assess the effect of planting date on aflatoxin concentrations in grain from knife‐wound inoculated ears during a five‐year study at Tifton, GA. We also evaluated the relationship between aflatoxin concentrations in maize grain and several environmental variables, especially those involving temperature and moisture. Five plantings of Funk's G‐4507 were made in 1982, six in 1983 and 1984, and 10 in 1986 and 1987. Average planting dates varied from about 1 March to 1 August. Eight to 12 wound‐inoculated, 10‐ear samples were assayed per planting date. Aflatoxin concentrations were not significantly related to insect damage or the percentage of ears with visible Aspergillus flavus Link ex Fries, but concentrations were correlated with maximum and minimum daily temperature and net daily evaporation during 20‐ to 40‐d and 40‐ to 60‐d periods following full silk. Combined and average correlations for these relationships were highly significant. Regressions of aflatoxin concentrations on planting date revealed a significant linear decrease in concentration (200–300 ppb per 15‐d delay in planting) from early to late. Simple coefficients of determination of 0.75 or greater also suggest a significant relationship when measured over periods of more than 1 yr. Early plantings in Georgia are believed to be at higher risk because the critical grain filling period, beginning 20 d after silking, falls when the seasonal maximum and minimum temperatures are highest and when net evaporation is at its peak.