By Dusty Sonnenberg, CCA, Ohio Field Leader, a project of the Ohio Soybean Council and soybean check-off.

Weed control in soybeans and herbicide trials have been the subject of research conducted in the Becks Practical Farm Research (PFR) the last several years. Getting back to the basics of herbicide application and tank mixing, and even the water used as a carrier are important considerations. “Most of the water used for spraying is well water which has varying degrees of hardness,” said Luke Schulte, Field Agronomist for Becks. “Anything about 125 parts per million is considered hard. The calcium and magnesium present in the water are cations that make water hard and can interfere with herbicide performance.”

The use of ammonium sulfate (AMS) to condition spray water is important for multiple reasons. “AMS has two roles. The first role is as a Nitrogen source to bond and magnetize with the weak acids herbicide to help move it into the plant,” said Schulte. “The second is to provide an adequate supply of Sulfur to provide a negative charge to magnetize and occupy the positively charged calcium, magnesium and sodium and prevent them from tying up the herbicides. Liberty is one of the most sensitive herbicides to inadequately conditioned water, followed closely by glyphosate and Enlist.”

The form of AMS used should also be a consideration.  The effectiveness of the herbicide is dependent on how the water is conditioned, and the form and rate of AMS being used. “In PFR research, both dry AMS and liquid AMS were studied. The research found that a low use rate liquid AMS is not the same as a dry AMS, and results showed that the AMS component used can lead to a 13-15% performance difference in how Liberty responded,” said Schulte. “It is difficult to get the same amount of sulfate into a low use rate liquid AMS as there is in a dry AMS, and as a result there are performance differences.”

When applying a contact herbicide, spray volume is important. “Gallons matter,” said Schulte. “When using Liberty, we saw a 12% advantage when we increased from 15 up to 20 gallons per acre.

Photo Credit: Erdal Ozkan, OSU Extension State Specialist, Sprayer Technology

Liberty is a contact herbicide. With the cost of the herbicide increasing, I want to make sure I get the most out of what I apply, and by simply increasing the water volume we increased the effectiveness of the herbicide. The cheapest thing we will add to the tank to increase effectiveness when applying Liberty is more water.”

Spray droplet size is also a factor to consider. “For Liberty and glyphosate applications, a medium size droplet is ideal; not a course droplet like we use with dicamba and Enlist,” said Schulte. “Spray timing is also important. Ideally with Liberty we want to spray in the heat of the day.”

Products like Enlist have multiple factors to consider to be most effective. “Often farmers ask if they should use glyphosate or Liberty with Enlist,” said Schulte. “Enlist with Liberty showed a near 30% advantage in water hemp control for weeds that escaped the pre-emerge application followed by the post tank mix in PFR research conducted in southern Illinois.

Mature Waterhemp

In an Enlist system for water hemp control in a post application it really needs to have the addition of Liberty.”

It is important to consider the weed spectrum of the field when planning the herbicide program. “Enlist plus glyphosate is a very good program for ragweed, both common and giant ragweed,” said Schulte. “When it comes to Marestail, if it survived the pre-application, and when it comes to water hemp, for post-emergent control, Enlist really needs Liberty with it. This provides two sites of action working on the glyphosate resistant water hemp and Marestail. Work at North Dakota State encourages growers to have patience and use more water when working with Enlist. They actually suggest waiting 5 minutes after adding the dry AMS before adding Enlist, and if using liquid AMS, to wait 2 minutes before adding the Enlist.”

Staying on top of weed pressure is important. “The University of Nebraska found that in 60 bushel beans at current commodity prices, for every growth stage we delay weed control waiting for plant canopy, it costs $20 in yield,” said Schulte.

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