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) a nd one which does not (chisel), were used before sowing wheat after va rious crop successions combining eyespot host and non-host crops. Soil structure was nearly the same and crop residues were located in the d ifferent soil layers. Eyespot sporulation was estimated by visually as sessing pot plants which had been on the trial plots for a fixed lengt h of time. Field plants were also assessed for disease at several whea t growth stages. A kinetic equation expressing disease level as a func tion of degree-days was fitted to the disease levels observed on the f ield plants. This equation is based on eyespot epidemiology and depend s on two parameters reflecting the importance of the primary and the s econdary infection cycles respectively. Pot plant and early field plan t disease levels and primary infection were closely correlated to the presence of crop residues in the top layer. The amount of residues dep ended on both crop succession and soil tillage. Where the previous cro p was a host crop preceded by a non-host crop, soil inversion buried h ost residues, thus decreasing the primary infection risk. Where howeve r the previous crop was a non-host crop preceded by a host crop, soil inversion carried the host residues back to soil surface, thus increas ing the primary infection risk. Secondary infection was not correlated to either crop succession or soil tillage.