The Role of Alternative Hosts and Herbicides in the Management of Clavibacter nebraskensis, Causal Agent of Goss’s wilt of Corn
thesisposted on 03.01.2019, 20:46 by Joseph T. Ikley
The reemergence of Goss’s wilt of corn in the western Corn Belt in 2006, along with subsequent identification of the disease in 16 states, has led to renewed interest in the disease and its epidemiology. Goss’s wilt, caused by the bacterium Clavibacter nebraskensis, is currently the third-leading cause of yield loss in corn from diseases in the United States. Its impact is exacerbated by the fact that cultural control methods are the only current means for its control. The objectives of our research were to (1) determine the role that alternative hosts of the bacterium play in the disease cycle and epidemiology of Goss’s wilt, and (2) determine if postemergence herbicide use affects disease severity. Through a greenhouse experiment, we discovered three new weedy alternative hosts of the disease. In a series of field and greenhouse experiments, we found that C. nebraskensis can overwinter on alternative host and corn debris in Indiana. We found that C. nebraskensis did not become seed-borne in alternative hosts. In contrast to corn, no systemic infections were observed on alternative hosts, with the bacterium being restricted to inoculated leaf tissue. Using herbicides to control C. nebraskensis-infected weeds did not reduce the pathogenicity of the bacterium recovered from treated plants. The use of nicosulfuron, dicamba plus diflufenzopyr, and a 2X rate of glyphosate postemergence increased disease severity in one experiment, but postemergence herbicides did not influence disease severity in a second experiment. Corn yield was not affected. This indicates that herbicide use may play a role in the epidemiology of Goss’s wilt in some years, but ultimately corn yield is not affected. Our results demonstrate that the host range of C. nebraskensis is wider than previously thought, and that postemergence control of alternative hosts may not be sufficient in reducing inoculum levels. Our results suggest that failure to control alternative hosts could negate some of the benefits of crop rotation to reduce inoculum levels in a field, thus playing an important role in the epidemiology of Goss’s wilt.