Posted on Dec 01, 2009
Sorghum downy mildew (SDM), caused by the fungus Peronosclerospora sorghi, is emerging as a potential constraint to sorghum production in the Upper Gulf Coast counties of Texas. Initially, there was the emergence of a metalaxyl-resistant isolate in 2001 in Wharton County, which was followed by the emergence of a new metalaxyl-resistant pathotype that overcame some sources of host resistance in 2005. Experiments in Wharton county demonstrated a disease incidence of up to 24% in susceptible hybrids. The new pathotype has spread within Wharton County and in 2008, was found in Victoria County. Although there is currently research evaluating new sorghum germplasm and new fungicides for management of SDM, we are proposing to increase educational efforts to more intensively promote existing IPM (integrated pest management) practices for managing this disease in the short term (i.e. the next few years) and integrating new germplasm or fungicides as they become available into a control program over a longer period of time. We propose to conduct extensive surveys for SDM in an eight-county area of the Upper Gulf Coast. We will map locations of SDM and identify the pathotype and metalaxyl sensitivity. We will conduct demonstration trials of hybrids with resistance to the prevailing pathotype in several counties, assessing both disease severity and yield, in comparison with susceptible yields. We will also perform trials demonstrating the effectiveness of crop rotation. We will promote these trials with field days and county meetings, as well as publish the results. Educational bulletins will be developed and disseminated via mailings and the internet. The efforts will be coordinated by a plant pathologist, but will rely heavily on the contributions of a multi-disciplinary team of agronomists and entomologists, since factors in addition to disease resistance will affect the yield of a hybrid. The integration of efforts will be at a regional level through extension specialists and IPM agents, as well as at a county level through county agents. This area of Texas accounts for 8% of the yield for the state, but represents a value of the crop of $67 million (2008 statistics: 13.5 million bushels @ $5/bu). A widespread presence of SDM in this area could conceivably result in a yield loss of millions of dollars, which our proposed educational efforts would avert. Our efforts could be transferred to other sorghum production areas of the United States, where SDM could become a problem in the future.