Developing Management Tools for Sunflower Rust (Puccinia Helianthi)

Sunflower rust, caused by Puccinia helianthi (Schwein), is an economically important disease in North Dakota. Since 2008, sunflower rust incidence and severity have increased. Therefore, a four year study was initiated to examine the management strategies for the disease. A total of 19 fungicide efficacy and timing trials were conducted from 2008-2011. Results indicated that DMI and QoI chemistries can be used effectively to manage the disease. Timing trials indicated that disease control was highest when fungicide applications were made at R5.0-R5.8. Results indicate a fungicide application is warranted when rust severities at approximately 1% are found on the upper-four leaves at R5. To observe phenotype variability in the pathogen, a P. helianthi survey was completed in 2011 and 2012. Single-pustule isolates were obtained and virulence phenotypes were evaluated on a set of nine differentials. Race characterization was assigned based on virulence phenotypes. In 2011, the most commonly detected races were 300 and 304, while the most virulent was 776. In 2012, races 304 and 324 were the most commonly detected and the most virulent was 777. To identify new sources of rust resistance, the core-set of Helianthus annuus germplasm was obtained from the USDA-North Central Regional Plant Introduction Station. The accession lines were screened both in the greenhouse and the field. The accessions were screened in the greenhouse individually to races 300, 304, 336, 337, and 777. Lines were screened in the field to a mixture of P. helianthi isolates coding to 300, 304, 336, and 337. The majority of lines were susceptible in both the field and greenhouse. At both field locations, PI 431538, PI 432512, and PI 650362 had year-end severities under 1%. Similarly, PI lines 432512 and 650362 had resistant infection types across all five races. The results of these studies provide information and tools that are being used currently to manage rust and will contribute to management in the future.National Sunflower AssociationNorth Dakota Department of Agricultur