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Abstract
The aerial concentration of ascospores and macroconidia of Gibberella zeae (anamorph Fusarium graminearum) within small inoculated plots was measured over 2 years (1999 and 2000) in Manitoba. In July 1999, a 30 m × 30 m area was inoculated with corn kernels infested with G. zeae. Ten Rotorod spore samplers were set up in a line transect, trapping airborne ascospores of G. zeae from 1800 to 0200. Ascospore concentration was high 1 to 4 days after rainfall exceeding 5 mm. Daily ascospore concentrations ranged from 0 to 214 m−3. Daily macroconidial concentrations ranged from 0 to 42 m−3. In 2000, a 3 m × 3 m area was inoculated with corn kernels infested with G. zeae, and a Burkard 7-day spore sampler was set up in the centre. Higher numbers of both ascospores and macroconidia were trapped in 2000 than in 1999. The airborne concentration of ascospores started to increase between 1500 and 1700 and coincided with the lowest daily relative-humidity values. Ascospores continued to be trapped until 0400. The highest concentration of ascospores occurred at 2100, with a maximum of 15 233 m−3. Fewer ascospores were trapped between 0500 and 1400, ranging from 0 to 167 m−3. As in 1999, high ascospore concentrations were detected after rainfall exceeding 5 mm. Compared with the number of ascospores, fewer macroconidia were trapped, with daily concentrations ranging from 0 to 567 m−3. An increased understanding of airborne inoculum is important for developing local-risk assessment models and strategies for managing fusarium head blight.