And how did your waterhemp crop do this year?
Since the waterhemp family has both male and female plants whose genes mix annually, the genetic diversity increases every year and an increasing number of plants have become resistant to a wider variety of herbicides. Johnson and Nice say, “Currently, waterhemp populations resistant to ALS-inhibitors, triazines, diphenylethers (PPO-inhibitors), and glyphosate (Roundup) have been identified.” They say the first to fail were the ALS-inhibitors, such as Pursuit and Accent. The next to fail were PPO-inhibitors, such as Reflex, Ultra Blazer, and Cobra. And with the widespread use of glyphosate, it did not take long for it to fail as a control alternative. With all of that great news, what can you do to control a nasty waterhemp infestation in your best cropland?
For corn, Johnson and Nice recommend:
1) A pre-plant or pre-emergent to either control or suppress it, mixed with atrazine.
2) A post emergent treatment if the population is dense or continued rain promotes more germination.
3) Post emergent treatments include 2,4-D, dicamba, Status, Callisto, Laudis, Corvus, Impact, or glyphosate if you are using GT corn. Ignite and atrazine will control small waterhemp in Liberty Link corn.
For soybeans, Johnson and Nice recommend:
1) A pre-plant or pre-emergent herbicide that contains Authority, Valor, or Dual.
2) A post-emergent herbicide that controls later emerging plants should include Ultra Blazer, Cobra, Reflex, Flexstar, or Ignite for Liberty Link soybeans. Those should be applied when waterhemp plants are less than 4 inches tall.
3) Glyphosate with Warrant or Outlook (for Roundup Ready soybean) can be effective where the waterhemp population is not resistant to glyphosate and provide residual control.
Waterhemp has become a headache for many Cornbelt farmers because of its unique ability to become genetically diverse. That means many herbicides, which initially would control waterhemp will no longer suffice. A strategic plan has to be developed for farms which have waterhemp populations that are resistant to one or more herbicide modes of action. For both corn and beans, that includes the use of both a pre-plant and a post emerge treatment.
Source: FarmGate blog