Weed resistance has been developing for a long period of time in Minnesota and North Dakota. Resistance to ALS inhibitors was first documented in ND in 1987. The first documented weed resistance in Minnesota was Common Lambsquarters resistance to atrazine in 1982. Unfortunately, Giant Ragweed and Common Waterhemp have now been documented to be resistant to glyphosate in sugarbeet producing counties in southern Minnesota. Common Ragweed has been documented to be resistant to glyphosate in several RRV counties. Common Waterhemp has also been documented to be resistant to glyphosate in the southern RRV. Wild oat resistance in several RRV counties has also been documented to grass herbicides. To preserve use of glyphosate on Roundup Ready® sugarbeets its imperative growers take immediate steps to proactively prevent resistant weed development in all crops in the rotation.
The 2011 growing season had weather that was more suitable for Cercospora than any year in recent memory. For example, the Prosper NDAWN station has had 15 days as of August 8 with SEVERE two day infection values.
Even the St. Thomas and Forest River NDAWN stations have had 6 days of SEVERE ratings. Cercospora was found in all growing areas as of late July. Very good disease management plans have been implemented by most growers. Continue the excellent management plans with a timely Headline application in late August or very early September.
University of Minnesota research has documented reduced frost injury benefits of timely Headline application, see photos. Most growers and agriculturists have also observed these results.
Never let resistant weeds go to seed.