Impact of agronomic practices on populations of Fusarium and other fungi in cereal and noncereal crop residues on the Canadian Prairies

Fusarium head blight (FHB) is an important disease which has been causing damage to wheat and barley crops in western Canada. Because crop residues are an important source of inoculum, it is important to know the ability of Fusarium spp. to colonize and survive in different residue types, and how their populations might be affected by agronomic practices. Sampling of residue types on producers’ fields for quantification of Fusarium and other fungi was conducted in 2000–2001 in eastern Saskatchewan. Fusarium spp. were isolated from most fields, whereas their mean percentage isolation (MPI) was over 50% for cereal and pulse residues, and under 30% for oilseed residues. The most common Fusarium, F. avenaceum, had a higher MPI in pulse and flax (45–48%) than in cereal or canola (10–22%) residues. This was followed by F. equiseti, F. acuminatum, F. graminearum, F. culmorum and F. poae which were isolated from all, or most, residue types. Factors affecting Fusarium abundance in residues included the current crop, cropping history, and tillage system. In cereal residues, the MPI of F. avenaceum was higher when the current crop was another cereal (24%) versus a noncereal (4–8%). When the current crop was another cereal, the lowest MPI of F. avenaceum and F. culmorum occurred when the field had been in summerfallow (SF) two years previous (F. avenaceum: 17% for SF, 28% for a crop; F. culmorum: 1% for SF, 4% for a crop); in contrast, F. equiseti and Cochliobolus sativus were most common in residues of cereal crops preceded by SF (F. equiseti: 16% for SF, 10% for a crop; C. sativus: 22% for SF, 13% for a crop). The MPI of F. graminearum was higher when the crop two years previous was an oilseed (7%) versus a cereal (4%). In regards to tillage effects, when the current crop was a cereal, the MPI of F. avenaceum was higher under minimum (MT) and zero tillage (ZT) (22–37%) than conventional tillage (CT) (15%), that of F. graminearum was lowest under ZT (3% for ZT, 7–11% for CT-MT), whereas that of C. sativus was highest under CT (27% for CT, 6–11% for MT-ZT). Under ZT, previous glyphosate applications were correlated positively with F. avenaceum and negatively with F. equiseti and C. sativus. These observations generally agreed with results from previous FHB and root rot studies of wheat and barley in the same region. Percentage isolation of F. avenaceum from noncereal and of F. graminearum from cereal residues were positively correlated with FHB severity and percentage Fusarium-damaged kernels of barley and wheat caused by the same fungi.