Cultivar rotation as a strategy to reduce leaf diseases under barley monoculture

A 3-year experiment was established in 1998 to determine whether barley cultivar rotation could be used to reduce the impact of leaf diseases while maintaining crop productivity. Treatments consisted of various sequences of two cultivars with varying degrees of scald and net blotch resistance, 'Kasota', and 'AC Lacombe'; a previously scald-resistant cultivar 'CDC Earl'; a susceptible check, 'Harrington'; and a nonhost, triticale, cultivar 'Wapiti'. In 1998, significant differences in scald severity occurred among the barley cultivars tested. In 1999, significant rotation differences occurred for scald and net blotch severity as well as for PCR-based assay results for scald infection of grain. In general, disease severity was highest and yield was lowest when a barley cultivar was grown on its own residue, especially for cultivars other than 'Kasota'. Contrasts indicated that yield and kernel weight were lower, while scald and net blotch levels and PCR-based assay results were higher, for barley cultivar monoculture than for barley cultivar rotation. In 2000, when a barley cultivar was grown on its own residue, scald severity was usually higher compared with barley cultivar rotation. A similar trend was also observed for net blotch, except for the cultivars 'Kasota' and 'CDC Earl'. Poor stand establishment in some plots precluded the detection of yield differences among some treatments in 2000. Contrasts for 2000 indicated that higher levels of scald and net blotch, and decreased kernel and test weights, occurred for barley cultivar monoculture compared with barley cultivar rotation. In both 1999 and 2000, barley planted on triticale residue generally had higher yield, higher kernel weight and test weight, and lower disease levels compared with barley planted on barley residue. Barley cultivar rotation can be used as a short-term strategy to help reduce leaf disease levels and maintain crop productivity for Alberta barley producers, when rotational options are limited because of livestock feed requirements or market factors. However, long-term sustainable leaf disease management likely would require the introduction of rotations with alternative crops such as triticale, or the implementation of other methods of adding diversity, to cropping systems focused on the intensive production of livestock feed.