INFLUENCE OF CROP MANAGEMENT ON EYESPOT DEVELOPMENT AND INFECTION CYCLES OF WINTER-WHEAT

Wheat was assessed at four crop growth stages for eyespot (anamorph Ps eudocercosporella herpotrichoides, teleomorph Tapesia yallundae) in a series of field trials that studied the effects on disease frequency o f five wheat management techniques (sowing date and density, nitrogen fertiliser dose and form, removal/burial of cereal straw). An equation expressing disease level as a function of degree-days was fitted to t he observed disease levels. This equation was based on eyespot epidemi ology and depended on two parameters illustrating the importance of th e primary and the secondary infection cycles respectively. Cultural pr actices were classified according to the importance of their effects o n disease, and these effects could be related to infection cycles and host plant architecture. Sowing date had the earliest and strongest ef fect; early sowing always increased disease frequency through the prim ary infection cycle, and its influence on the secondary cycle was vari able. Disease frequency was increased by high plant density and/or a l ow shoot number per plant through primary infection; the secondary cyc le was, however, decreased by a low shoot number per plant, which redu ced late disease development at high plant density. High nitrogen dose s increased disease levels and the severity of both infection cycles, but this effect was partly hidden by a simultaneous stimulation of til lering and thus an indirect decrease of disease incidence. When signif icant, ammonium (vs ammonium nitrate) fertiliser decreased eyespot lev els and infection cycles whereas straw treatment (burial vs removal of straw from the previous cereal crop) had no effect.