Aflatoxin contamination of maize kernels before harvest. Interaction of Aspergillus flavus spores, corn earworm larvae and fungicide applications.

Two maize (Zea mays L.) hybrids with varying degrees of resistance to damage by corn earworm (CEW) (Heliothis zea Boddie) were grown in Iowa, Georgia, and Missouri. Treatments included: introduction of Aspergillus flavus Link ex. Fr. spores onto newly-emerged silks, application of a fungicide as an aqueous spray onto test ears during the first three weeks after flowering, infestation of ears with CEW eggs, and combinations of these variables. CEW larvae were collected from developing ears and examined for the presence of internal A. flavus group propagules. Aflatoxin levels were determined in mature kernels. Toxin concentrations exhibited a distinct regional variation with relatively high levels in Georgia samples, intermediate concentrations in Missouri kernels and low levels in Iowa samples. No treatment effects were noted in Georgia samples but introduction of A. flavus and CEW increased toxin accumulation in Missouri kernels. Although the CEW-susceptible hybrid exhibited a trend towards increased damage by the insect, no treatment-related differences were observed in the presence of the fungus in larvae or in aflatoxin contamination. Fungicide applications did not significantly reduce aflatoxin levels in mature kernels.