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Effect of Residue Management on Wetness Duration and Ascocarp Production by Pyrenophora tritici-repentis in Wheat Residue. W. Zhang, Graduate research assistant, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506-5502; W. F. Pfender, associate professor, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506-5502. Phytopathology 82:1434-1439. Accepted for publication 25 August 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-1434.

No-till, mowed, and disked residue treatments were applied to wheat residue infested with Pyrenophora tritici-repentis in fields near Manhattan, KS, in 1988 and 1989. Ascocarp production by P. tritici-repentis and straw-wetness duration were studied in relation to these treatments and four straw positions relative to the soil surface (above-soil and near-soil; upper part and lower part of standing stubble). Ascocarp production, estimated by counting ascocarps on sampled straw, was significantly affected by straw position and tillage treatment. The number of ascocarps per gram of straw in near-soil straw was only 32 and 42% of that found in the above-soil straw in mowed and no-till treatments, respectively. The difference in the disked treatment was significant only in 1989. In the standing stubble of no-till plots, the number of ascocarps in the lower part of the stubble was only 12% of that found in the upper part. The number of ascocarps per square meter of field area was reduced by 91% in disked and by 69% in mowed treatments compared with the no-till treatment. Straw wetness was monitored by connecting electrodes to individual straws in the field. The number of straw-wetness hours occurring in wetness periods longer than 12 h (long-period wetness hours) varied with straw position. There were higher numbers of long-period wetness hours in near-soil straw than in above-soil straw in all three tillage treatments. A negative correlation was found between ascocarp production and long-period wetness events in the mowed and no-till treatments.

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