Interaction of net blotch and scald on barley

Abstract

Net blotch caused by Pyrenophora teres f. sp. teres and scald caused by Rhynchosporium secalis are major foliar diseases of barley (Hordeum vulgare) and often occur together in the same fields in central Alberta, Canada. The differential development of these two diseases in relation to seeding date was investigated in five field trials in 2001 and 2003 under natural infection conditions. Significantly higher scald severity on barley was observed in all trials with early seeding (from early to mid May) as compared with late seeding (from late May to early June). Scald severity tended to be higher than net blotch severity in the early seeding date trials, whereas net blotch severity was generally higher than scald severity with late seeding. The differential development of disease severity between net blotch and scald was likely affected by temperature, host resistance, and natural inoculum. The interaction of the development of P. teres and R. secalis on barley ‘Harrington’ was investigated in artificially inoculated field plots in 1993 and 1995. In 1995, a mixture of both inocula induced a greater area under the disease progress curve (AUDPC) and caused a greater grain yield reduction than either inoculum alone in both seasons. No difference in grain yield was observed among plots in which P. teres or R. secalis were inoculated separately for either season. The disease progression and yield reductions observed in the present study indicate an additive effect as a result of the interaction between the two pathogens attacking the same plant. Early seeding of scald susceptible barley cultivars should be avoided in scald-infested fields in central Alberta. Scald susceptible cultivars may be seeded late for swath grazing of barley to escape scald infection.