| Adoption of genetically modified glyphosate-resistant crops around the world has increased the selection pressure for weedy species resistant to the commonly applied herbicide glyphosate. Experiments were conducted to examine C. canadensis adaptations that facilitate seed dispersal and population spread. Early fall and early spring emerging plants grew taller, set seed earlier, and produced 80,000--100,000 more seeds than late spring emerging plants. Management of glyphosate-resistant C. canadensis should be effective on early fall and early spring emerging plants since they may be contributing to a greater extent to the spread of the glyphosate resistance gene than late spring emerging plants.;Exploration of seed release and escape from the surface boundary layer (SBL) was conducted by vertical and aerial seed sampling in concert with micrometeorological measurements. Vertical sampling was conducted in 2005 and 2006 in Pennsylvania using a 6 m vertical sampler positioned 14 m downwind of a C. canadensis point source. Thermal turbulence were greatest in the afternoon sampling periods which corresponded with the greatest seed collection at 5 and 6 m, the heights above which seed are escaping the SBL. Only 0.04% of seed were predicted to be collected at 5 and 6 m on the vertical sampler, equating to 52 seeds per plant (out of 130,000) predicted to be escaping the SBL. Using the same vertical samplers, remotely piloted airplanes were included in sampling events to quantify the seed concentration profile extending from ground level to 120 m. More seeds (54%) were predicted to escape from the SBL during the afternoon than during the morning (37%), which correlated with maximum mechanical turbulence rather than thermal turbulence. Most seed dispersal studies report dispersal distances of tens of meters, but C. canadensis seed collected aerially will stay aloft for 5-7 hours and were predicted to travel 20 to 100 km.;A spatially explicit model was developed to assess the changes in glyphosate-resistant (GR) C. canadensis spread rate as the agricultural landscape varied with genetically modified GR crop adoption. The model predicted that after 5 years with the current GR adoption in soybean (89%) and corn (21%), 80% of the possible 360 fields would be infested. Adding alfalfa into the current or increased adoption scenarios reduced the number of infested fields after 5 years by 10%. The greatest reduction in spread was accomplished by reducing the amount of glyphosate-resistant crops on the landscape. When encountering a wind dispersed species, like C. canadensis, which can easily move among fields, decisions about weed management are not made independent of decisions in neighboring fields, but instead are coupled. |
