Epidemiology and Chemical Control of <i>Fusarium</i> Seedling Blight of Winter Wheat (<i>Triticum aestivum</i> L.)

Fourteen seed lots of winter wheat were tested for Microdochium nivale contamination using various methods. The seed lots tested were largely free from other fungal contaminants and M. nivale was both superficial and deep seated. No relationship between seed weight and M. nivale contamination was shown. Microdochium nivale contaminated seeds were evenly distributed by weight throughout the three seed lots tested and no relationship between seed appearance and contamination was shown. Seedling disease symptoms were greatest for M. nivale in cold dry conditions and for F. culmorum in warm dry soil conditions. Good linear relationships were shown between disease severity and the rate of seedling emergence for both artificially inoculated and naturally contaminated seed. Contamination by M. nivale affected seedling vigour as measured by the rate of emergence. Seedlings took longer to emerge as the percentage of M. nivale contaminated seeds increased. Microdochium nivale var. majus was shown to be the most common sub-group of M. nivale isolated from wheat seed. Of 91 M. nivale isolates tested 85 were identified as M. nivale var. majus and 6 as var. nivale, with the var. majus isolates being more pathogenic towards wheat seedlings. The efficacy of fungicide seed treatments was not affected by inoculum load as measured by the percentage of contaminated seed. However, reduced temperature did decrease the efficacy of one of the fungicides tested. In the field, effects on crop emergence and infection were observed following seed treatment at two sites. At one site disease control resulted in an increase in grain yield of 300%. It is clear that seedling disease will be severe when a seed lot with a high percentage of contaminated seeds is sown into conditions where seedling emergence will be slow. Under such conditions the use of a robust seed treatment is advised