Waterhemp continues to be the weed of discussion this time of year in northern Illinois. The lack of rainfall has led to waterhemp escapes in soybean fields, and now the race is on to keep ahead of the weed pressure. In this article, I intend to shed light on which herbicide mixes have been most effective for us.
43 oz of Liberty 280 SL and 28 oz of Buc 5 Xtra, seven days after application. Photo by Seth Wiley, Ogle County, Illinois.
Attacking waterhemp starts with the soybean trait that was planted. In Enlist E3-traited soybeans, you have at least three post-applied herbicide options:
- Glyphosate (Roundup)
- Glufosinate (Liberty)
- 2,4-D choline (Enlist One)
- 2,4-D choline and glyphosate (Enlist Duo)
*Enlist One, Enlist Duo, or glufosinate can be applied through the R1 growth stage.
Glyphosate has virtually zero effectiveness on waterhemp. I add glyphosate to the tank mainly for grass control, but I have noticed that glyphosate and glufosinate seem to have a synergy when tank-mixed. However, glufosinate is doing most of the heavy lifting against waterhemp.
A few bullet points for a successful glufosinate application:
- Minimum of 20 GPA of water (I’ve gone up to 25 GPA before)
- Glufosinate is a contact killer that needs to cover all growing points.
- 3 lbs/ac of AMS minimum
- Glufosinate needs ammonium to work effectively.
- Most adjuvant combinations have some amount of AMS in them, but you may need to add some more AMS to reach the 3lbs/ac.
- Hot sunny day with relative humidity above 30%
- Temperatures need to be above 75 degrees to ensure the weed is actively growing.
The worst day to spray glufosinate is a cool, cloudy day with low humidity. Generally, the perfect day for humans is the worst day for glufosinate. The days when everybody is searching for a pool in the summer are the days of best control with glufosinate. However, it can be too hot to spray. I was always taught to go by the rule of 160: If heat and humidity add up to more than 160, you are more likely to see herbicide flashing on crops.
Waterhemp density, height, and weather forecast dictate when to add 2,4-D choline to the mix. In my experience, 2,4-D choline by itself is only effective on waterhemp 3 inches or shorter. In northern Illinois, we stayed cool throughout most of May. If we needed to make an herbicide application in soybeans for waterhemp, 2,4-D choline was our best option because conditions were not hot enough to ensure the weeds were actively growing for a glufosinate application to be effective.
Mixing 2,4-D choline and glufosinate together is the most effective mix against thick patches of waterhemp taller than 3 inches. According to label guidelines, waterhemp should not exceed 6 inches when applying 2,4-D choline and glufosinate. 2,4-D choline is a systemic herbicide; it does not need to cover every growing point like glufosinate to combat waterhemp. However, 2,4-D choline struggles to take down larger waterhemp plants and needs glufosinate to assist. In a perfect world, we should not let the waterhemp grow taller than 3 inches, but we do not live in a perfect world most days.
43 oz of Liberty 280 SL and 28 oz of Buc 5 Xtra, seven days after application. Photo by Seth Wiley.
As you can see in the picture above, glufosinate did not cover the bottom growing points of this waterhemp plant. Even though the plant is stunted, it will keep pushing new growth from the growing points at the bottom of the waterhemp plant. This is why 2,4-D choline and glufosinate must be mixed to take out the larger waterhemp plants. The systemic characteristics of 2,4-D choline help glufosinate take down waterhemp more effectively. Both herbicides have strengths and weakness, but together they are the best option for controlling waterhemp.
As always read and follow label instructions.
Sources:
About the Author: Seth Wiley
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