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Influence of Temperature and Five Fungicides on Rhizoctonia Root Rot of Hard Red Winter Wheat. J. T. Mathieson, Research Associate, Texas Agricultural Experiment Station, Bushland 79012. C. M. Rush, Professor, Texas Agricultural Experiment Station, Bushland 79012. Plant Dis. 75:983-986. Accepted for publication 24 April 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0983.

Rhizoctonia root rot is a disease associated with early-planted hard red winter wheat in the Texas Panhandle. Studies were conducted to determine the effect of temperature and fungicide seed treatment on disease development. The fungicides tested included triadimenol, imazalil, difenoconazole, UBI1886, and Nusan + Nuzone. When wheat plants were grown in soil infested with a known pathogenic isolate of Rhizoctonia solani, anastomosis group 4 (AG-4), at five constant temperatures ranging from 15 to 35 C, emergence decreased significantly (P = 0.05) as temperatures increased (R2 = 0.50). Fungicides were tested for their ability to inhibit growth of R. solani in vitro on amended potato-dextrose agar and for disease control in infested soil at 15, 25, and 35 C. No fungicide greatly reduced mycelial growth in vitro at concentrations ≤ 0.1 μg a.i./ml, but at concentrations of 1 g/ml or greater, all fungicides significantly reduced growth. Seed treated with triadimenol had significantly greater emergence and dry matter production at each temperature compared with other treatments. Seed treated with triadimenol had significantly less infection, both on the seed and coleoptile, for 25 days after planting in soil infested with R. solani compared with the untreated check.