Gradients of tan spot of winter wheat from a small-area source of Pyrenophora tritici-repentis.

Wheat plots (15.2×15.2 m) were established near Manhattan and Hesston, Kansas, to measure changes in area under the disease progress curve (AUDPC) with distance from a small-area (0.6×0.6 m) source of Pyrenophora tritici-repentis. At both locations during 2 yr, relatively steep gradients of tan spot occurred away from the primary inoculum. Exponential decay equations significantly (P<0.0001) fit data and estimated that a 90% reduction in AUDPC occurred at 3.6-5.4 m from the source. These results indicate that disease spread by primary and secondary inoculum is limited in Kansas, and that fields where P. tritici-repentis does not occur will not be affected greatly by neighboring, diseased fields [...]