By Tom Peters
Weed identification was an important topic of emphasis during the winter meeting season. The message was proper identification of cotyledon to first true leaf weeds to make the correct herbicide selection decisions. Potted plants (with labels to reinforce teaching) were often used to teach plant characteristics. Broadleaf weeds are starting to emerge in fields and agriculturalists are faced with weed identification challenges (without the benefit of labels).
Pigweed is beginning to germinate and emerge in fields in eastern North Dakota and Minnesota and identification is very difficult when they are at the cotyledon stage. Two important pigweed species farmers are trying to differentiate are redroot pigweed and waterhemp. Redroot pigweed cotyledons are narrow and linear whereas waterhemp cotyledons tend to be more egg shaped (see images). First true leafs are perhaps the best distinguishing feature; redroot pigweed leaves are rounded and tend to have a dimple on the margin of the leaf at the midrib. Waterhemp true leaves are long and narrow (lanceolate).
There is an excellent on-line technical bulletin, developed by Kansas State University called, ‘Pigweed Identification, a pictorial guide to the common pigweeds of the Great Plains’. The bulletin can be found at, https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=236&pubId=1754