Resistance to herbicides has been a management challenge as long as herbicides have been used for weed control. The introduction of crops with engineered resistance to glyphosate in 1996 prompted most growers to adopt a technology that was easy and efficient.
Now, as with other herbicides, some weeds are growing resistant to glyphosate. To date, glyphosate resistance has been confirmed in 24 weed species worldwide, including 15 in North America.
According to Mark Jeschke, agronomy research manager for DuPont Pioneer, some of these weeds had previously developed resistance to other herbicides. In the Midwest, for example, common waterhemp is a real problem. Other weeds that are showing resistance include horseweed (marestail), common and giant ragweed and Palmer amaranth.
Jeschke provides the following guidelines to help manage resistant weeds.