** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** PHOMOPSIS STEM CANKER IS A DISEASE THAT DECREASES SUNFLOWER (HELIANTHUS ANNUUS) YIELDS IN MINNESOTA (MN), NEBRASKA (NE), NORTH DAKOTA (ND), AND SOUTH DAKOTA (SD), WHICH TOGETHER ACCOUNT FOR OVER 80% OF SUNFLOWER PRODUCTION IN THE U.S. CURRENTLY, WE RECOMMEND APPLYING A SINGLE DOSE OF QUINONE OUTSIDE INHIBITOR (QOI) FUNGICIDE DURING THE MINIATURE FLORAL HEAD GROWTH STAGE OF SUNFLOWERS TO MANAGE THIS DISEASE. THIS TREATMENT CAN SIGNIFICANTLY REDUCE THE SEVERITY OF PHOMOPSIS STEM CANKER (UP TO 30% REDUCTION) AND INCREASE YIELD (BY 5%). HOWEVER, IN 2022, WE DISCOVERED THAT DIAPORTHE HELIANTHI, ONE OF THE MAIN FUNGI RESPONSIBLE FOR PHOMOPSIS STEM CANKER, HAS DEVELOPED COMPLETE RESISTANCE TO QOIS DUE TO A G143A MUTATION (A SUBSTITUTION OF GLYCINE (G) WITH ALANINE (A) AT AMINO ACID POSITION 143). OUR LONG-TERM RESEARCH OBJECTIVE IS TO ENHANCE IN-SEASON MANAGEMENT OF PHOMOPSIS STEM CANKER BY ADOPTING AN INTEGRATED APPROACH AND IMPROVING FARMERS' RETURN ON INVESTMENT (ROI). OUR PROJECT AIMS TO: (1) DETERMINE THE PREVALENCE OF QOI-RESISTANT STRAINS OF D. HELIANTHI AND D. GULYAE, THE FUNGI CAUSING PHOMOPSIS STEM CANKER, IN MN, ND, NE, AND SD; (2) EVALUATE THE EFFECTIVENESS OF FOLIAR FUNGICIDES CONTAINING SUCCINATE DEHYDROGENASE INHIBITOR (SDHI) AS AN ALTERNATIVE TO QOIS ON HYBRIDS RESISTANT TO DIAPORTHE; AND (3) ENHANCE FARMERS' AND AGRICULTURAL PROFESSIONALS' CONFIDENCE IN MANAGING PHOMOPSIS STEM CANKER BY DEVELOPING AND PROVIDING EXTENSION TOOLS. THE EXPECTED OUTCOMES OF THIS PROJECT ARE INCREASED YIELDS AND ROI FOR FARMERS THROUGH THE INTEGRATION OF FOLIAR FUNGICIDES AND DIAPORTHE-RESISTANT HYBRIDS, WHILE ALSO RAISING AWARENESS OF THE POSSIBLE PRESENCE OF QOI-RESISTANT STRAINS CAPABLE OF CAUSING PHOMOPSIS STEM CANKER IN THEIR FIELDS.?