INFLUENCE OF CROPPING SYSTEM ON SHARP EYESPOT IN WINTER-WHEAT

Wheat was assessed for sharp eyespot in three field trials using facto rial designs which investigated preceding crops and soil tillage effec ts (inversion vs non-inversion), soil structure (compacted vs non-comp acted) and wheat management techniques (sowing date and density, nitro gen fertiliser rate and form, removal or burial of cereal straw). A pr evious host vs non-host crop increased sharp eyespot. The effect of so il tillage depended on crop succession: if the previous crop was a hos t, soil inversion vs non-inversion decreased disease by burying infect ious host crop residues; if the previous crop was a non-host itself pr eceded by a host, soil inversion vs non-inversion increased disease by carrying infectious material back to the soil surface. Uncompacted vs compacted soil increased sharp eyespot, but only at early stages. Ear ly sowing always increased disease. High plant density (giving rise to low tillering) increased early and decreased late disease levels. A h igh vs low nitrogen rate and a low vs high ammonium content of the fer tiliser slightly increased sharp eyespot. Removal or burial of straw d id not affect disease. A hierarchy of the factors was established: cro p succession and soil tillage were dominant factors; among the wheat m anagement practices, only sowing date and plant density had important effects. (C) 1997 Elsevier Science Ltd.