ARS | Publication request: The effect of temperature on Rhizoctonia disease development and fungicide efficacy in controlling Rhizoctonia root rot on sugarbeet

Submitted to: Sugarbeet Research and Extension Reports
Publication Type: Proceedings
Publication Acceptance Date: February 9, 2009
Publication Date: March 2, 2009
Repository URL: http://hdl.handle.net/10113/34131
Citation: Khan, M.F., Quandah, I., Bolton, M.D. 2009. The Effect of Temperature on Rhizoctonia Disease Development and Fungicide Efficacy in Controlling Rhizoctonia Root Rot on Sugarbeet. 2008 Sugarbeet Research and Extension Reports. 39:252-254.

Interpretive Summary: Rhizoctonia solani is a soil-borne pathogen that causes Rhizoctonia root and crown rot of sugarbeet. A strain of the fungus called AG 2-2 IIIB is widely distributed in many sugarbeet growing areas and is highly virulent. Therefore, we conducted studies to learn more about the biology of this pathogen and tested the ability of three fungicides to control disease development. Trials were conducted using growth chambers set at four different temperature regimes (10, 15.6, 21.1 and 26.7°C). No disease development occurred at 10 and 15.6°C. However, significant disease development occurred at both 21.1 and 26.7°C during the two-week post inoculation evaluation period. Several classes of fungicides were tested at 26.7°C since this was the temperature most conducive to disease development. Application of azoxystrobin and prothioconazole at the full label rate completely controlled the disease while application of difenoconazole at the full label rate was not effective at controlling disease caused by R. solani AG 2-2 IIIB.

Technical Abstract: Rhizoctonia solani AG 2-2 is the causal agent of Rhizoctonia root and crown rot in sugarbeet. Since the intraspecific group AG 2-2 IIIB is considered to be more virulent than AG 2-2 IV, our objectives were to monitor disease development of AG 2-2 IIIB infection at four different soil temperatures under controlled climate conditions. A second objective was to determine the efficacy of three fungicides at the temperature determined to be optimal for disease development. Trials were conducted using growth chambers set at four different temperature regimes (10, 15.6, 21.1 and 26.7°C). No disease development occurred at 10 and 15.6°C. However, significant disease development occurred at both 21.1 and 26.7°C during the two-week post inoculation evaluation period. Efficacy of several classes of fungicides was tested at 26.7°C since this was the temperature most conducive to disease development. Application of azoxystrobin (0.672 L ha-1; full label rate) and prothioconazole (0.365 L ha-1; full label rate) completely controlled the disease while application of difenoconazole (0.511 L ha-1; full label rate) was not effective at controlling R. solani AG 2-2 IIIB.