GIANT RAGWEED IS AN ECONOMICALLY DESTRUCTIVE NATIVE PEST THAT ENDANGERS AGRICULTURAL PRODUCTION AND PUBLIC HEALTH. IT IS THE MOST COMPETITIVE ANNUAL WEED IN ANNUAL GRAIN CROP PRODUCTION IN THE U.S. AND A GROWING PROBLEM IN FIBER CROP PRODUCTION. MANAGEMENT OF GIANT RAGWEED IS EXACERBATED BY ITS RAPID EVOLUTION OF HERBICIDE RESISTANCE: FROM A RECENT SURVEY, HERBICIDE-RESISTANT GIANT RAGWEED OCCURRED IN MORE THAN HALF OF RESPONDING COUNTIES ACROSS THE U.S. CORN BELT. ALSO, THE POLLEN OF RAGWEEDS IS RESPONSIBLE FOR MORE THAN HALF OF ALL HAYFEVER CASES IN NORTH AMERICA, MAKING IT ONE OF THE MOST IMPORTANT AEROALLERGENS IN THE U.S. GIANT RAGWEED HAS ATTRACTED GLOBAL ATTENTION AS AN INVASIVE SPECIES IN EUROPE AND ASIA WHERE ITS THREAT TO AGRICULTURE, PUBLIC HEALTH AND BIODIVERSITY OF NATIVE ECOSYSTEMS ARE BEING INTENSIVELY ASSESSED. STRICT LIMITS ON GIANT RAGWEED SEED TOLERANCES IN GRAIN EXPORTED TO CHINA THREATEN U.S. GRAIN EXPORTS. GIANT RAGWEED IS SPREADING TO NEW CROPPING AREAS WITHIN AND BEYOND NATIVE HABITATS IN THE OHIO RIVER VALLEY, BUT ITS PATHWAYS OF SPREAD AND THE MECHANISMS BY WHICH IT INVADES CROP FIELDS ARE POORLY UNDERSTOOD. A MAJOR FACTOR CONTRIBUTING TO THIS LACK OF UNDERSTANDING IS THAT GIANT RAGWEED'S INVASIVENESS VARIES GEOGRAPHICALLY DESPITE ITS NEAR-UNIVERSAL PRESENCE IN NON-CROP EDGE HABITATS ACROSS THE U.S. CORN BELT. A SIMILAR GEOGRAPHIC PATTERN OCCURS IN EUROPE. THE IMPORTANCE OF NON-CROP POPULATIONS IN GIANT RAGWEED DISPERSAL TO NEW CROP LOCATIONS AND THE ADAPTIVE CAPACITY OF LOCAL INVADERS IS UNKNOWN. A CLEAR UNDERSTANDING OF THE PATHWAYS BY WHICH GIANT RAGWEED SPREADS ACROSS THE LANDSCAPE AND THE MECHANISMS BY WHICH IT INVADES CROP FIELDS IS CRUCIAL FOR PREDICTING AND PREVENTING ITS ESTABLISHMENT IN NEW ENVIRONMENTS AND IS THE RATIONALE FOR THIS PROPOSAL.WE PROPOSE TO IDENTIFY THE SOURCES OF INVASIVE GIANT RAGWEED POPULATIONS, THE PATHWAYS BY WHICH IT SPREADS, AND THE MECHANISMS BY WHICH IT INVADES AND PERSISTS IN CROP AND NON-CROP HABITATS THROUGH AN INTEGRATED APPROACH THAT COMBINES DEMOGRAPHIC AND GENETIC ANALYSES CONDUCTED AT REGIONAL SCALE. THE PROPOSED RESEARCH IS FOUNDED ON EXTENSIVE PREVIOUS RESEARCH THAT HAS LED US TO HYPOTHESIZE THAT GIANT RAGWEED INVADES AND ADAPTS TO CROP FIELDS FROM LOCAL NON-CROP POPULATIONS IN DIFFERENT LOCATIONS AND AT DIFFERENT TIMES DUE TO GEOGRAPHIC VARIATION IN SEED AND SEEDLING EMERGENCE TRAITS THAT PROVIDE DIFFERENTIAL ADAPTIVE CAPACITY DEPENDING ON LOCAL CROP PRODUCTION PRACTICES. THE EXPERIMENTAL APPROACH WE PROPOSE WILL PROVIDE A COMPREHENSIVE TEST OF THIS HYPOTHESIS. OUR PROPOSED RESEARCH IS SIGNIFICANT BECAUSE THE RESULTS WILL IMPROVE OUR ABILITY TO PREDICT, PREVENT, AND MANAGE NEW INVASIONS, BASED ON A MUCH MORE COMPLETE UNDERSTANDING OF THE DISPERSAL PATHWAYS OF INVASION ACROSS THE U.S. CORN BELT AND THE GROWTH, REPRODUCTIVE BIOLOGY, AND SOIL SEEDBANK DYNAMICS OF LOCAL POPULATIONS ACROSS THE REGION. THE RESULTS WILL EXTEND TO OTHER CONTINENTS WHERE GIANT RAGWEED IS SPREADING AS AN INTRODUCED INVASIVE WEED. THE PROPOSED RESEARCH WILL ALSO CONTRIBUTE TO ECOLOGICAL THEORY BY TESTING A MODEL OF INVASION BIOLOGY THAT CAN BE GENERALIZED TO OTHER SPECIES WITH SIMILAR BIOLOGICAL CHARACTERISTICS, INCLUDING RIPARIAN ORIGINS, OUTCROSSED MATING SYSTEM, HIGH HETEROZYGOSITY, LARGE-SEEDEDNESS AND A HIGH DEGREE OF PHENOTYPIC VARIABILITY. FINALLY, THE PROPOSED RESEARCH WILL YIELD A COMPREHENSIVE REFERENCE TRANSCRIPTOME AND OTHER GENOMIC TOOLS FOR GIANT RAGWEED, GREATLY FACILITATING FUTURE RESEARCH IN POPULATION GENETICS AND ADAPTATION FOR A SPECIES THAT IS RAPIDLY INCREASING ITS GLOBAL REACH AND IMPACT.