On a December episode of RFD-TV Live! with Syngenta, a caller posed the question, "If you don't have resistant weeds now, but have farmers two or three counties away that are seeing problems, how long does it take to move to unaffected fields?"

Reid Smeda, weed scientist at the University of Missouri, responded, "We've been looking at that with common ragweed, which has a fairly large seed and isn't going to move very quickly. We're more concerned about farmers moving equipment with growers farming in more than one county, and many times hundreds, or thousands, of acres. We're also concerned about moving pollen around. Some of our studies with common ragweed suggest that within one field, we can move pollen up to 250 feet. It doesn't take long for it to jump a fence row or highway and move from one field to another.

"Horseweed, on the other hand, has a small apparatus that allows it to be airborne, allowing it to move many hundreds of feet. It's important to realize that with a weed like that, even though you're doing the right things from one year to the next, that you have not caused it to be resistant, it can come from a neighbor's field."

Bryan Young, weed scientist at Southern Illinois University, also a guest on the program, agreed. "We'd had the horseweed, or marestail, issue in southern Illinois that exploded on us since 2005. I'd also like to mention that even if you don't have resistance, and it's in your region, it's well justified to implement resistance management strategies that would improve overall control of weed species that might threaten your operation, which may be resistant in adjoining areas. A lot of the practices that we advocate to delay resistance are also good agronomically to potect your crop yield."