EFFECTS OF CROP-ROTATION AND RESIDUE MANAGEMENT-PRACTICES ON SEVERITY OF TAN SPOT OF WINTER-WHEAT

Tan spot (caused by Pyrenophora tritici-repentis) severity was determined for wheat (Triticum aestivum) grown in rotation with sorghum (Sorghum bicolor), which allowed a 15-mo break between wheat crops, and was compared with severity in wheat grown continuously. Three wheat residue management schemes were used within each crop sequence: chisel plow, V-blade, and no-till for the wheat-sorghum rotation and moldboard plow, chisel plow, and no-till for continuous wheat. Tan spot severity was determined during 4 yr; multiple ratings were taken in the last 2 yr for the calculation of area under the disease progress curve. For continuous wheat production, plowing significantly reduced tan spot throughout the season relative to the other tillage practices. Rotation to sorghum was as effective as plowing for control of tan spot; however, in one of the 4 yr, early season tan spot was noted in the wheat-sorghum rotation with no-till. Under certain conditions, crop rotations as short as 1 yr controlled tan spot.