Evolution In Action: Glyphosate-Resistant Weeds Threaten World Crops

Glyphosate is by far the world's most widely used and important herbicide because it is efficacious, economical and environmentally benign. Glyphosate dominates for non-selective weed control in agricultural ecosystems, especially to remove weeds between rows in established perennial tree, nut, vine crops and before seeding of annual crops. Globally, glyphosate is also the non-selective herbicide of choice in urban and industrial areas, national parks and other amenity areas. In these use patterns, there have been few instances of weeds evolving glyphosate resistance. While there are documented cases of glyphosate-resistant weed evolution in several countries given the long term glyphosate usage, experience establishes that plants cannot easily evolve resistance to this herbicide. The common factor in those examples where glyphosate-resistant weeds have evolved is very persistent glyphosate usage with little or no diversity in weed control practices. Unsurprisingly, glyphosate resistance has evolved most often in the resistance-prone genera Conyza and Lolium. It is important to recognise, however, that glyphosate continues to be effective globally in its traditional use patterns for non-selective weed control where there is sufficient diversity in control practices and not an extreme over-reliance on glyphosate. However, this situation has dramatically changed now that glyphosate has become a selective herbicide in transgenic crops.