Oral Technical Session: Disease Control and Pest Management

195-O

Sensitivity of Rhizoctonia solani to SDHI and DMI fungicides.
O. AJAYI (1), C. A. Bradley (2)
(1) Univ of Illinois At Urbana-Champaign, Urbana, IL, U.S.A.; (2) University of Illinois, Urbana, IL, U.S.A.

Rhizoctonia solani, is an important seedling pathogen of soybean in the United States. Seed treatments in the demethylation inhibitor (DMI) and succinate dehydrogenase inhibitor (SDHI) fungicide classes are used to manage seedling disease caused by R. solani. Baseline sensitivities of R. solani to two SDHI fungicides (penflufen and sedaxane) and two DMI fungicides (ipconazole and prothioconazole) were determined in in vitro assays. Baseline isolates originated from four different states (IL, OH, ND, MN) and had been isolated prior to 2000. Isolates recovered in 2012 and 2013 from Illinois were tested for sensitivity to SDHI fungicides. The effective concentration of the fungicide that inhibited mycelial growth by 50% (EC50) was determined for each isolate. For the baseline isolates, the range of EC50 values for penflufen, sedaxane, ipconazole, and prothioconazole was 0.01-0.49, 0.02-0.49, 0.21- 5.47, and 0.20-5.58 ug/ml, respectively, with respective means of 0.07, 0.09, 1.74, and 2.15 ug/ml. For the 2012 and 2013 isolates, the mean EC50 values were 0.09 and 0.16 ug/ml, and ranges were 0.01-0.48 and 0.04-0.45 ug/ml, respectively for penflufen and sedaxane. The establishment of the baseline sensitivities to these fungicides serves as a first step in monitoring fungicide resistance development in populations of R. solani affecting soybean in the north central states.