Debunking "superweeds"

This report brief got my attention:

http://wssa.net/wp-content/uploads/WSSA-Fact-Sheet-on-Superweeds_16-Sep-2014.pdf

Weed scientists report that the problem of herbicide resistance in weeds is primarily due to an evolved resistance due to repeated application of one class of herbicide. Using an approach integrating a variety of methods of weed control - many physical, not just chemical - could lessen this effect.

While genes from genetically engineered canola, wheat and sunflower can enter wild relatives, and do sometimes, GM corn, soy and cotton don't have any wild relatives in the US and Canada, so gene flow is negligible.