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Effect of MSO and AMS on Group 14 Herbicides (05/26/16)

Glyphosate-resistant kochia has been identified in several locations across North Dakota. This raises the question as to how emerged kochia will be controlled without glyphosate.

Effect of MSO and AMS on Group 14 Herbicides

Glyphosate-resistant kochia has been identified in several locations across North Dakota. This raises the question as to how emerged kochia will be controlled without glyphosate. Group 14 herbicides include Sharpen, Aim, Spartan, and Valor. There are several premixes that also contain these Group 14 herbicides such as Spartan Charge (Spartan + Aim), Authority MTZ (Spartan + Metribuzin), Fierce (Valor + Zidua), etc. We have known for many years that foliar activity with Sharpen is much more effective when applied with AMS + MSO. Preplant and desiccation studies showed greater weed control with MSO > COC > NIS. Aim and Valor are used as desiccants and have also been shown to be more effective with AMS + MSO. We have known that you don’t want to apply Spartan after crop emergence due to potential crop injury, but never believed that Spartan had as much foliar activity as Sharpen and Aim.

We conducted studies from 2013-2015 to help answer the question of how to control emerged glyphosate-resistant kochia in preplant or preemergence applications. We came across this inadvertently, but in the studies we applied herbicides with and without AMS and MSO. I expected Sharpen + AMS and MSO to control kochia, but did not expect good control from Spartan or Authority MTZ. It was apparent that all the Group 14 herbicides provided much better kochia control when tank mixed with AMS + MSO. As a follow-up, we conducted a greenhouse study to confirm what we were seeing in the field (see picture). Again, the Group 14 herbicides provided good kochia control when tank mixed with AMS + MSO. We did not include Valor in the study, but assume Valor will also provide better kochia control with AMS + MSO. (Continued next page)

In the 2013 and 2014 field studies, kochia control was good to excellent. However, in 2015, kochia control was much lower than the previous two years. One of the main differences may have been that in 2015, temperatures were much lower during and after application. Thus, in 2015, even with AMS and MSO, the Group 14 herbicides provided only fair kochia control, possibly due to cold temperatures. Thus, under optimal spring temperatures, I expect kochia control with Group 14 herbicides will be enhanced with the addition of AMS + MSO.

Several people have asked “What about other weeds? Will we see enhanced control of other weeds as well?” I believe it is possible that we will see enhanced control of other annual weeds. However, one of my concerns is the effect on perennial weeds. For example, we have observed that the rapid desiccation provided by Sharpen will reduce Canada thistle control by glyphosate. Thus, my recommendation is that if Canada thistle is one of your primary targets, you should not tank mix glyphosate with Sharpen. We have not observed antagonism with Sharpen + glyphosate on annual weeds. We are currently conducting a study with dandelion, where we have glyphosate applied alone compared to glyphosate applied with all Group 14 herbicides to determine if the Group 14 herbicides antagonize dandelion control with glyphosate.

Brian Jenks

Weed scientist, North Central R&E Center, Minot

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