Effects of planting date and environmental factors on fusarium ear rot symptoms and fumonisin B1 accumulation in maize grown in six North American locations

Fusarium ear rot, primarily caused by Fusarium verticillioides, causes losses in grain yield and quality and can result in contamination of grain by mycotoxins, primarily fumonisin B₁. Disease severity and fumonisin B₁ contamination vary considerably among maize‐growing regions and from year to year. A 2 year field study was conducted in six locations in the USA, to evaluate the roles of planting date, maize hybrid, rainfall, temperature and insect pests in the variation in fusarium ear rot symptoms and fumonisin B₁ contamination. Grain samples were inspected to determine percentage of kernels with fusarium ear rot symptoms, categorized as ‘moulded’ or ‘starburst’; grain was also analysed by ELISA for fumonisin B₁. Hybrid and planting date frequently had significant effects (P ≤ 0·05) on fusarium ear rot and fumonisin B₁ contamination. Earlier planting consistently resulted in lower ear rot severity, fumonisin B₁ levels and insect damage. Mould symptoms were highly correlated with thrips populations (Frankliniella occidentalis) (r = 0·78) and with fumonisin B₁ concentration (r = 0·89). The starburst symptom was not as closely correlated with thrips (r = 0·33) or fumonisin B₁ (r = 0·18). A multiple linear regression model identified highly significant effects on fumonisin B₁ for thrips, lower average daily precipitation after flowering, and location. These results strengthen the evidence that locations with high populations of ear‐infesting thrips and dry conditions after pollination have an increased risk of fumonisin contamination, and suggest that high fumonisin levels are much more likely in visibly moulded kernels compared to those with ‘starburst’ symptoms.