The main leaf spotting diseases of spring wheat in western Canada are tan spot and the septoria leaf blotch complex. Tan spot is most prevalent in drier areas, whereas septoria leaf blotch is more prevalent under moist conditions. All wheat cultivars currently registered for use in western Canada are susceptible to leaf spots. Some cultivars have been shown to possess adult plant resistance to tan spot. Durum wheat cultivars are more susceptible to tan spot than common wheat, whereas common wheat is mostly affected by septoria leaf blotch. A study conducted in southern Saskatchewan during 1991-1993 showed that the relative prevalence of leaf spotting fungi in durum and common wheat cultivars was affected mainly by weather factors, whereas location affected their relative leaf spotting score. In recent years, there has been a steady increase in the incidence of leaf spotting diseases throughout western Canada, which has been attributed to above-average precipitation and adoption of conservation tillage practices. At present, the most common cropping systems for wheat are a rotation with summer fallow or a broadleaf crop, or continuously cropped wheat. These cropping systems have been increasingly managed using reduced tillage practices. The effect of different crop management practices on leaf spots was examined in two studies conducted at Swift Current, Saskatchewan, during 1993- 1996. Leaf spot severity was higher in wheat after fallow than in continuous wheat, under both conventional tillage practices designed to conserve residues and under no-till management. Wheat grown under no-till had similar leaf spot severity as conventional-till wheat. Continuous wheat and wheat grown after a non-cereal crop had similar leaf spot severity, except in years with high disease pressure, when a continuous wheat system had higher disease levels. Examination of crop residues collected at seeding suggested that differences among treatments could be related to the higher density of infective structures of leaf spotting fungi on residues from two seasons before than on those from the immediately previous crop. This is likely due to environmental conditions throughout the winter not being conducive to fungal growth and to the development of infective structures on the new residue. Crop residues in the no-till treatments had a lower density of fungal structures than those in conventional tillage systems. Glyphosate used for weed control in the no-till treatment may have had an inhibitory effect on fungal growth. ln addition, there was a higher leaf spot severity in treatments with N deficiency in wet years, and a lower severity of leaf spots in treatments with P deficiency in years that had a cool and wet spring.

English

9806|AGRIS 9802

Jose Juan Caballero

I1705031

CIMMYT Publications Collection