A corn disease foliar survey has been conducted in North Dakota since 2014. The information obtained from this survey has provided valuable information documenting corn diseases in North Dakota. This is extremely important to growers when it comes to hybrid selection and the appropriate use of fungicides. Results from the survey have determined that two diseases commonly occur in the state; common corn rust and Goss’ wilt. The incidence of these diseases have varied from year to year, however common corn rust continues to be the most prevalent disease. Common corn rust rarely needs to be managed as most northern hybrids have adequate resistance. However, several hybrids are susceptible to Goss’ wilt and significant yield losses can occur.
Goss’ wilt is the most important corn disease in North Dakota. Since it is caused by bacterium, fungicides and other chemical products are not an effective means of control. The best management tool is using less susceptible hybrids, crop rotation and tillage (when appropriate). To help value the importance of hybrid selection with Goss’ wilt, yield loss trials were conducted from 2015-2017. Research plots were inoculated at growth stage V8-V12 (8 to 12 leaves present) and/or VT (tasseling). Summarized data from the six trials demonstrated that mean yield losses of 41% occurred on a susceptible hybrid when inoculated at both V8-V12 and VT (Figure 1). Another way to look at this data is if a producer assumes a susceptible hybrid has 180 bu/A yield potential, an early season infection by the Goss’ wilt pathogen may reduce yields to 106 bu/A in infected areas (Figure 1).
Understanding the causal agent of a disease is important for future management of Goss’ wilt. It has been well documented that several plant pathogens have changed over time in numerous cropping systems. In order to understand Goss’ wilt risk in ND, more information is needed on the biology of the pathogen. Fifty Goss’ wilt pathogen isolates were collected from 2013-2017 and were used to assess aggressiveness (how quickly the pathogen spreads on leaf tissue). Lesion length was measured for several days to determine if certain isolates produce disease symptoms faster than others. Genotypic analyses using DNA from the isolates will help detect any potential genes that influence aggressiveness. The information will aid future breeding efforts as well as document any changes in the pathogen.
The research listed above has covered several areas of corn disease research. The corn foliar disease survey has identified important foliar diseases of corn and has guided research efforts on Goss’ wilt. The yield loss studies exemplify the importance of hybrid resistance when managing Goss’ wilt. The aggressiveness study and genotypic analyses will help understand the biology of the pathogen and provide a foundation of knowledge for the Goss’ wilt pathogen in ND. The information generated from this research has been used in Extension talks, presented at scientific conferences, and has influenced decision making for corn growers in North Dakota.