In soybeans, PPO herbicides that are being applied at planting are Reflex and Valor. Additionally, there are a lot of premix products available for at-planting residual weed control in soybean that contain a PPO herbicide. Some that come to mind are Authority XL, Authority MTZ, Prefix, Fierce, Verdict, Envive, and Broadaxe.

I routinely talk about the need for using multiple effective modes of action against pigweed or any other resistant-prone weed as a means of protecting herbicides against resistance. Many premixes are touted as an excellent tool for resistance management because multiple modes of actions are comprised within the premix.

Unfortunately, many of these are recommended at rates that fall far short of the use rate recommended for each active ingredient alone. There are likely three reasons for recommending a lower rate when applying two products together.

First, if Palmer pigweed is one of the weeds we are targeting with the premix and both of the components alone are effective on pigweed, an application can still achieve effective control by reducing the rate of each of the components.

Herein lies a problem. Now we have a reduced rate of each component and there is a wealth of recent research showing that reduced rates of herbicides contribute to resistance.

Second, reducing the rate of the combination is one means of allowing a company to remain competitive while offering “multiple” herbicides in a premix.

Third, for some herbicides such as metribuzin, it is my belief that use of this herbicide in a premix is often recommended at a low rate to ensure that there are no tolerance issues when applying the product in soybean.

 

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The problem here is that the metribuzin component is lowered to the point that a sensitive soybean variety will not be injured by the metribuzin, but in turn the rate is so low that the metribuzin provides marginal pigweed control. I actually took a look at several products this past summer and when I applied metribuzin alone at the low rate contained within the premix, the result was utter failure on pigweed.

Again, metribuzin is an excellent herbicide that needs to be on more acres of soybean. If you are over 40 years old, you most likely remember metribuzin as Sencor, but today there is no Sencor available for use in soybean – it is only registered for use in turf. Today, straight-run metribuzin is sold for use in soybeans by Mana, Loveland, and UPI under the trade names of Tricor and Metribuzin.

Next time you plant soybeans, consider applying a full rate of metribuzin in areas where pigweed has been a major problem and don’t forget to plant a tolerant soybean variety. I think you will be impressed with the level of pigweed control.

 

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