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1. Glyphosate-resistant Conyza canadensis populations now infest more than 44 000 ha of arable land in eastern USA, only 5 years after the first resistant population was reported. Seed dispersal, the expansive use of glyphosate and the lack of tillage are all factors contributing to this high invasion speed. 2. Seed collected from deliberately established C. canadensis source populations were found at the furthest seed traps in our empirical studies, providing one of the most complete dispersal kernels for studying long-distance dispersal. The results indicate that seed regularly disperses at least 500 m from source populations. While a relatively small number of seeds moves long distances, 99% of the seed was found within 100 m of the source. 3. Empirical and mechanistic models were fitted to the data to predict the dispersal in the prevailing wind direction. Both models underestimated seed deposition beyond 200 m but the mechanistic model provided a better fit to the data (lower Akaike information criterion). A two-dimensional analysis examined the correlation between angular directions of wind and seed movement. All trials were anisotropic but only the cumulative wind and seed direction were significantly correlated ( P < 0·05). 4. The empirical model was used to explore the effect of increasing source strength, which would be expected as an infestation of glyphosate-resistant C. canadensis expands on a producer's farm. At infestation levels consistent with a heavy infestation in a 5-ha field, seed dispersed further than 1·5 km, easily affecting 10s to 100s of surrounding farms. 5. Synthesis and applications. Emigration of C. canadensis seed, from a source farm to adjacent farms, means that population dynamics and weed management are dependent on both intra- and interfield dispersal phenomena. Wind-dispersed plants challenge the common practice of single field management as a viable management option for herbicide-resistant weeds. Farms coupled by seed dispersal require proactive management practices by every producer to prevent and minimize the development of glyphosate-resistant infestations of undesirable and alien plants. [ABSTRACT FROM AUTHOR]

Background: Provisia™ rice (PV), a non-genetically engineered (GE) quizalofop-resistant rice, will provide growers with an additional option for weed management to use in conjunction with Clearfield ® rice (CL) production. Modeling compared the impact of stacking resistance traits versus single traits in rice on introgression of the resistance trait to weedy rice (also called red rice). Common weed management practices were applied to 2-, 3- and 4-year crop rotations, and resistant and multiple-resistant weedy rice seeds, seedlings and mature plants were tracked for 15 years., Results: Two-year crop rotations resulted in resistant weedy rice after 2 years with abundant populations (exceeding 0.4 weedy rice plants m -2 ) occurring after 7 years. When stacked trait rice was rotated with soybeans in a 3-year rotation and with soybeans and CL in a 4-year rotation, multiple-resistance occurred after 2-5 years with abundant populations present in 4-9 years. When CL rice, PV rice, and soybeans were used in 3- and 4-year rotations, the median time of first appearance of multiple-resistance was 7-11 years and reached abundant levels in 10-15 years., Conclusion: Maintaining separate CL and PV rice systems, in rotation with other crops and herbicides, minimized the evolution of multiple herbicide-resistant weedy rice through gene flow compared to stacking herbicide resistance traits. © 2017 Society of Chemical Industry., (© 2017 Society of Chemical Industry.)