INFLUENCE OF CROP MANAGEMENT ON TAKE-ALL DEVELOPMENT AND DISEASE CYCLES ON WINTER-WHEAT

Wheat was assessed at four crop growth stages for take-all (Gaeumannom yces graminis var. tritici) in a series of field trials that studied t he effects of five wheat management practices: sowing date, plant dens ity, nitrogen fertilizer dose and form, and removal/burial of cereal s traw. An equation expressing disease level as a function of degree day s was fitted to the observed disease levels. This equation was based o n take-all epidemiology and depended on two parameters reflecting the importance of the primary and secondary infection cycles, respectively . Early sowing always increased disease frequency via primary infectio n cycle; its influence on the secondary cycle was variable. Primacy in fection and earliness of disease onset were increased by high density; however, at midseason take-all was positively correlated to the root number per plant, which was itself negatively correlated to plant dens ity. At late stages of development, neither plant density nor root num ber per plant had any influence on disease. A high nitrogen dose incre ased both take-all on seminal roots and severity of primary infection cycle but decreased take-all on nodal roots and secondary infection cy cle. Ammonium (versus ammonium nitrate) fertilizer always decreased di sease levels and infection cycles, whereas straw treatment (burial ver sus removal of straw from the previous cereal crop) had no influence.