Influence of Crop Rotation and Tillage on Rhizoctonia Bare Patch of Wheat

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Abstract
In a 3-yr field study in calcareous sandy loam soil, Rhizoctonia bare patch was more severe in direct drilled wheat than in wheat sown into cultivated soil. The areas of patches of stunted seedlings in direct drilled crops ranged from 5 to 13% (1981), 11 to 22% (1982), and 20 to 45% (1983) with no patches when soil was cultivated. The area of affected crop was consistently larger when wheat followed a mixed annual pasture of grasses and Medicago spp. than when wheat followed wheat, peas [Pisum sativum], or grassfree pasture of Medicago spp. Several potential root pathogens were isolated from rotted roots, but only Rhizoctonia-like fungi produced severe cortical rot and brown-tipped truncated roots similar to the symptoms on fieldgrown plants. Isolates identified as Rhizoctonia solani and Thanatephorus cucumeris were the most pathogenic of the Rhizoctonia-like fungi. All isolates of R. solani were pathogenic on wheat, barley, peas, Medicago spp., annual rye [Lolium rigidum], and barley grass [Hordeum glaucum].