VALLEY CITY, N.D. (NewsDakota.com) – The following is a news release from NDSU Extension Agent Randy Grueneich.
“The announcement in early September that Palmer Amaranth (Waterhemp’s nasty brother) had been identified in Barnes County was not welcomed news. This member of the “Pigweed Family” is known to have a faster growth rate and is more competitive with corn and soybeans so it could have a major impact on cropland in Barnes County. It also shares Waterhemp’s ability to produce a large amount (1 million) of seed on a healthy female plant. These tiny seeds can germinate every time we get a rain shower from April to September so the addition of soil activated herbicides to our weed control program is essential for season long control.
The days of a stand alone post applied weed control program are history when Waterhemp and Palmer Amaranth are present in a field. These Pigweed brothers are also resistant to Glyphosate (Roundup) so the pressure is on the tank mix partners alone to provide control in a post only application control program. Relying on the post tank mix alone may work when the pigweeds are small (2in or less) and we are close to crop canopy, but these pigweeds (4 in plus) have the ability to be burned black by an herbicide application and a few days later start sending out new growth. Even repeated applications do not kill the surviving plants and you end up with plants that will grow late in the season and produce a large amount of seed.
As you can see, when planning for Waterhemp control in fields in 20201 it’s important to include a soil active herbicide and make sure your post applications are to Waterhemp plants that are 2in or less. All this pressure that the Pigweed brothers can put on our weed control programs also means that we need to think beyond the herbicide program for long term success. Crop rotations that include multiple crops can help by expanding the herbicide options for control.
One example is putting spring wheat back into a crop rotation on fields with a severe Waterhemp infestation. Spring wheat allows for an early application window and has excellent early crop competition. Another option is to decease the row spacing when planting corn and soybeans. Narrow rows canopy faster and provide earlier competition for Waterhemp.
Tillage can be used to control emerged Waterhemp but shallow tillage does not bury seeds deep enough to reduce seed germination later in the growing season. The Pigweed brothers are determined and will continue to spread in 2021 so we also need to be determined and develop a plan stop them.”