By Mark VanGessel, Extension Weed Specialist; firstname.lastname@example.org
Working with Bill Bamka, County Extension Educator from Burlington County NJ, UD Weed Science Program confirmed that a population of common ragweed in New Jersey is resistant to glyphosate. The long-term history of the field is not known, but the past couple of years it was planted with soybeans. Last year, the preemergence herbicides did not provide adequate control and multiple applications of glyphosate were used postemergence. This is not the first confirmation of glyphosate-resistant common ragweed in the region; but the first in New Jersey. We have no reports of common ragweed resistant to glyphosate in Delaware.
In this situation, rotating to corn and use of atrazine is the best option. When rotating back to soybeans, use no-till because germination will be less than if tillage is done. The field will need to be treated with a preemergence application of cloransulam (i.e. Sonic or Gangster) or metribuzin (Tri-Cor, Boundary, or Canopy, generics). But there will definitely be a need for a postemergence herbicide and the best options would include Blazer Ultra, Cobra, Reflex, and Liberty (with Liberty Link soybeans). If cloransulam was not used at planting, FirstRate or Permit Plus (with STS soybeans) would also be options.