Application of the growth regulators chlormequat and ethephon and fertilization with nitrogen had no significant effect on the progress of head blight caused by Fusarium graminearum on the red spring wheat (Triticum aestivum) cultivar Max in greenhouse experiments in which heads were inoculated at anthesis with suspensions of macroconidia. A factorial field experiment was conducted in Quebec in 1991 with three variables: nitrogen (0 or 140 kg/ha), growth regulator (none, ethephon, or chlormequat), and inoculation (none, inoculation with macroconidia at anthesis, or inoculation 1 wk after anthesis). Because of dry conditions that year, no head blight symptoms developed on plants in the field. Seed infection by F graminearum was evaluated with a Fusarium selective medium. Nitrogen and growth regulators had no effect on wed infection. In 1992, a 3 X 3 factorial experiment was conducted in Ontario using the same growth regulator treatments and three inoculation treatments (no inoculation, heads inoculated with macroconidia, or rows infested with Fusarium-colonized corn kernels that produced ascospores). Both ethephon and chlormequat increased the incidence of spikelet infection, but only in treatments inoculated with infested corn. Chlormequat also increased the incidence of seed infection in noninoculated treatments and treatments with infested corn. These data suggest that growth regulators and nitrogen do not change the inherent susceptibility of wheat heads to F. graminearum, but shortened plants may be subject to higher inoculum doses because they art closer to ejected ascospores. The dwarfed plant architecture also may influence the microclimate and production of perithecia and ascospores by the perfect stage on the soil surface.
