Waterhemp and kochia are the top two weeds in South Dakota showing increasing resistance to glyphosate. South Dakota State Extension Weed Specialist Mike Moechnig says other weeds building glyphosate resistance are common ragweed – and, for no-till operations – horse weed or, marestail.
Moechnig says the time for growers to take action in managing glyphosate resistance is early when a patch is first noticed – before the seed bank has the chance to build up. Find areas where are few weeds are surviving among most that are not, he says.
The weed specialist says the other keys to management are to diversify herbicides and rotate corn, soybean and other crops. He recommends soil residual herbicides in corn fields and tank mix partners in soybean fields.