Efficacy of Azoxystrobin at Controlling Rhizoctonia solani at Early Growth Stages of Sugar Beet

Abstract

Sugar beet (Beta vulgaris L.) is one of the most profitable crops grown in Minnesota and North Dakota and makes a significant economic contribution to these States. Rhizoctonia damping-off and crown and root rot caused by Rhizoctonia solani Kühn, AG 2-2 are important soil borne diseases of sugar beet. Control strategy against this disease is achieved through timely application of effective fungicides before infection takes place. For many years, azoxystrobin was applied at or just prior to cultivation when sugar beets were at the 4-to 10-leaf stage to protect against crown infection and subsequent Rhizoctonia crown and root rot. Since 2009, warmer conditions in spring resulted in earlier planting and reports of seedling mortality and root rot caused by R. solani. The research objective was to determine whether azoxystrobin protects sugar beet seeds and seedlings to the 4-leaf growth stages against R. solani infection in a favorable environment. The experiment was conducted in the greenhouse with a temperature of 20±2 ˚C using sugar beet cultivar Crystal 539, susceptible to R. solani. Azoxystrobin was applied directly over the seed infurrow at planting, in an 18 cm band to soil covered seeds, and in an 18 cm band to cotyledonary, 2-leaf, and 4-leaf stages sugar beet. Fungicide application was followed by inoculation with R. solani AG 2-2 IIIB. Inoculated and non-inoculated (using sterile barley grains) controls were included for all the growth stages evaluated. There was no significant difference between the percentages of survivals in the non-inoculated controls compared to the sugar beet seed and different growth stages that were inoculated and treated with azoxystrobin indicating that the fungicide provided effective control of R. solani, irrespective of the sugar beet growth stages evaluated. Results indicated that sugar beet seeds and seedlings to the 4-leaf stages were susceptible to infection by R. solani in favorable environmental conditions. As such, necessary precautions should be taken to protect seeds and young plants especially when sugar beet is grown in fields with a history of the pathogen.