Waterhemp remains a big issue in our neck of the woods.
In the past year, fields near Interstate 74 and northward looked weedier than they have in several years, according to Dr. David Powell of GROWMARK. Weed resistance issues have showed up in recent years, which include ALS herbicides, Atrazine and PPO chemicals such as Cobra and Flexstar.
PPO resistance was observed in 2002 with Glyphosate resistance in 2005 and HPPD resistance in 2009. Roundup resistance is a major issue currently.
“We are using a lot of Roundup soybeans,” Powell said.
Powell notes there are three steps to manage waterhemp problems. Those steps include: using residuals before emergence, utilizing other chemistries and overlapping residuals. Growers should not even let weeds emerge.
“Without a residual pre, you will fail,” Powell admits.
There are only four different groups of herbicides growers can use pre-emergence to handle waterhemp in soybeans. Powell says sometimes it is good to incorporate herbicides. Liberty Link and Extend soybeans are coming to the market. With Liberty, you must understand the limitations to use it correctly. Liberty must be sprayed when weeds are small and the chemical really likes hot, humid weather.
“You’re going to have to get good coverage.”
Powell cautions against abandoning residual herbicides with Dicamba soybeans. Dicamba is a tool and conventional pre-herbicides are key.
“In three seasons, you can get Dicamba-resistant Palmer amaranth,” said Powell.
Farmers should not use old formulations – they should use newer ones that will be less risky.