Paul O. Johnson
Agronomy Field Specialist
Winter wheat and rye are off to a slow start in South Dakota with the cooler than normal temperatures. At the same time, winter annual weeds are growing fast despite cool temperatures. When we look at winter annual weeds, normally we include pennycress, tansy mustard, shepherd’s purse, green flower pepperweed, and several more winter annuals that get referred to as part of the mustard family. These weeds start out as a rosette in the fall and come on early in the spring. They grow well in cool temperatures and bolt, and flower, early in the season. Best control of these weeds is either before they start to flower or when it is apparent that some will be flowering in the next couple of weeks. Rye with normal growth does a very good job of shading the ground and keeps the weeds from developing, however in cool conditions this is not always the case.
With our current cool conditions, selection of the right herbicides is very important. Some herbicides can cause increased injury to the crop in cool conditions. Normally it is desirable to reach at least 50 degree weather to avoid this possibility. The Sulfonylurea herbicides (“SU” chemistry) are the main concern in cool temperatures. If bromoxynil is going to be used make sure there will not be a frost for at least three days following application. Always check the label of the product used to see if there are additional restrictions that need to be followed. For recommendations of products to use in small grain weed control refer to 2014 South Dakota Pest Management Guide Wheat. Copies may be obtained at the iGrow store under downloads, or contact your closest Regional Extension Center.
Source : SDSU