Distribution and prediction of Fusarium species associated with maize ear rot in Ontario

The incidence of Fusarium species associated with maize ear rot in Ontario, the role of air temperature and rainfall, and the routes of fungal entry (silk, insects, and birds) were investigated. Samples and observations over 56 locations and 151 genotypes in southwestern and east-central Ontario during 1991-1993 showed that five Fusarium species (F. subglutinans, F. graminearum, F. moniliforme, F. proliferatum, and F. sporotrichiodes) were present on infected kernels. Fusarium subglutinans was the most frequently isolated species and its occurrence was negatively correlated with cumulative rainfall in July, while F. graminearum incidence increased with precipitation. Fusarium moniliforme and F. proliferatum occurred mostly following the hot, dry summer of 1991. Physical injury to the ear from insects and infection through the silk on the ear tip were the major routes of fungal entry. A regression model calculated to estimate ear rot incidence explained 70% of ear rot field observations based on F, subglutinans and F. graminearum incidence, route of fungal entry, and variation in July cumulative rainfall, while a simplified model version accurately predicted ear rot incidence on 31% of observations made on 15 genotype-locations over a 2-year period.