RELATIVE OCCURRENCE OF PHAEOSPHAERIA-NODORUM AND MYCOSPHAERELLA-GRAMINICOLA ON SPRING WHEAT IN SASKATCHEWAN

The relative occurrence of Phaeosphaeria nodorum, causal agent of sept oria nodorum blotch, and Mycosphaerella graminicola, causal agent of s eptoria tritici blotch, on spring wheat cultivars planted into wheat s tubble varied with cultivar, location, and year. Little difference in the number of lesions of M. graminicola occurred on Kenyon, Katepwa, a nd Pembina. However, these lesions were found only rarely on Oslo, sug gesting that Oslo possesses resistance to this pathogen. In 1987 and 1 988, P. nodorum produced lesions on seedlings within three weeks of em ergence (early June), while M. graminicola lesions were not observed u ntil early to mid July. P. nodorum produced more lesions than M. grami nicola on all leaves sampled at Paddockwood in 1987. At Shellbrook, P. nodorum, was predominant on the penultimate leaf, but both pathogens were equally prevalent on the flag leaf. In 1988, P. nodorum was the p redominant pathogen on all leaves at both Shellbrook and Weirdale, whe reas M. graminicola produced only few lesions. Temperature and duratio n of leaf wetness periods appeared to have less effect on septoria nod orum blotch than on septoria tritici blotch. Septoria nodorum blotch d eveloped at all temperatures recorded, whereas both high (above about 25-degrees-C) and low (below 7-degrees-C temperatures delayed developm ent of septoria tritici blotch. Septoria nodorum blotch also developed when most leaf wetness periods were less than 11 h in duration, where as septoria tritici blotch required longer periods. Thus, in the Parkl and region of Saskatchewan if inoculum is present septoria nodorum blo tch will be a problem in most years, whereas septoria tritici blotch w ill be a problem only in years with moist conditions and moderate temp eratures.