The ability of weeds to evolve resistance to glyphosate has been well-documented.

Furthermore, the introgression of herbicide resistance between crops and weeds has been widely characterized. However, the transfer of herbicide resistance between different weed species is less well described in the scientific literature.

A recent publication in the American Journal of Botany [94 (4):660-673] “Transfer of glyphosate resistance: evidence of hybridization in Conyza (Asteraceae)” by Zelaya, Owen and VanGessel describes the introgression of a glyphosate resistance gene between Conyza canadensis (horseweed) and C. ramosissima (dwarf horseweed).

While the immediate implications on agriculture are not likely significant, the ability for herbicide resistance to move via pollen between weed species is indicative of the complexity of weed management in crops.

Prepared by Micheal D. K. Owen, extension weed management specialist, Department of Agronomy, Iowa State University