As the name of the weed suggests, waterhemp — a member of the pigweed family that affects soybean fields — thrives in areas where there’s been a lot of moisture. This year, that’s pretty much the entire country. Flooding exacerbates the spread of waterhemp, which a few years ago used to be a problem only in the South but has gradually made its way up to the northern United States. Now, to make matters worse for growers, scientists have discovered another strain of herbicide-resistant waterhemp.
According to the University of Illinois Extension, certain strains of waterhemp are now resistant to the Group 15 herbicide family. Extension experts note this includes herbicides with the following active ingredients: acetochlor, dimethenamid, metolachlor, pyroxasulfone and S-metolachlor. Waterhemp has also shown resistance to six other herbicide groups, including Group 2 (ALS inhibitors), Group 5 (triazines), Group 14 (PPO inhibitors), Group 9 (glyphosate), Group 27 (HPPD inhibitors) and Group 4 (2,4-D).
What does this mean for soybean growers? Growers will need to use multiple herbicide families, mixing up different modes of action. If they have a weed that’s resistant to whatever herbicide they’re using, multiple chemical families within your chemical program are a must. Start with clean fields and then come back with a post-emerge after the crop is up and weeds are within the legal range. You can even come back and spray a different family within the post-emerge, adding additional residual into the mix.
Growers who are using the Stine® Enlist E3™ soybean system this growing season will be at an advantage. Waterhemp shows itself to be increasingly problematic when it comes to single-mode or glyphosate-based soybean platforms. This reason is why we are so excited to see the Enlist E3 soybeans finally hit the market. So far, we have seen it in burndown scenarios, and the weed control of not just waterhemp but also marestail and other significant weeds has been absolutely fantastic! My expectation with all the rain we are receiving is that weed pressure will continue to be tremendous, and those weeds, especially waterhemp, will be very robust and tough to kill this year. Having a platform like Enlist E3 is a lifesaver because it offers three modes of action to tackle these weeds.
Experts note waterhemp can reduce yields by up to 44 percent. Each waterhemp plant has the ability to produce up to one million seeds, making it extremely problematic to control. At Stine, we’re working diligently to test different traits and herbicide modes of action in our test plots. Our goal with these plots, located in Adel, Iowa; Edgerton, Kansas; Cedar Rapids, Iowa; Windom, Minnesota; and Reynolds, Indiana, is to test what works best against weeds in general. We’re looking at different types of applications and chemistries to see what’s going to do a better job this year in controlling all weeds. And with the wet condition this year, it’s going to be interesting to see which herbicide combination really works the best and how the weeds affect yield.
Talk to your local Stine sales agronomist if you’re experiencing problems with waterhemp and other weeds this growing season.