SOIL TILLAGE AND EYESPOT - INFLUENCE OF CROP RESIDUE DISTRIBUTION ON DISEASE DEVELOPMENT AND INFECTION CYCLES

Two deep-working soil tillage tools, one which inverts soil (plough) and one which does not (chisel), were used before sowing wheat after various crop successions combining eyespot host and non-host crops. Soil structure was nearly the same and crop residues were located in the different soil layers. Eyespot sporulation was estimated by visually assessing pot plants which had been on the trial plots for a fixed length of time. Field plants were also assessed for disease at several wheat growth stages. A kinetic equation expressing disease level as a function of degree-days was fitted to the disease levels observed on the field plants. This equation is based on eyespot epidemiology and depends on two parameters reflecting the importance of the primary and the secondary infection cycles respectively. Pot plant and early field plant disease levels and primary infection were closely correlated to the presence of crop residues in the top layer. The amount of residues depended on both crop succession and soil tillage. Where the previous crop was a host crop preceded by a non-host crop, soil inversion buried host residues, thus decreasing the primary infection risk. Where however the previous crop was a non-host crop preceded by a host crop, soil inversion carried the host residues back to soil surface, thus increasing the primary infection risk. Secondary infection was not correlated to either crop succession or soil tillage.