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Why No AMS is Allowed with Dicamba in Dt Soybean (06/22/17)

Question: The chemical companies have told us that AMS is not allowed with dicamba on DT soybean. They say AMS will increase the volatility and may result in dicamba drift to susceptible plants and crops. They tell us what not to do but they don’t tell us why AMS increases volatility. What does AMS do?

Why No AMS is Allowed with Dicamba in Dt Soybean

 

Question:

The chemical companies have told us that AMS is not allowed with dicamba on DT soybean. They say AMS will increase the volatility and may result in dicamba drift to susceptible plants and crops. They tell us what not to do but they don’t tell us why AMS increases volatility. What does AMS do?

 

Answer:

BASF and Monsanto have taken two different approaches to restrict dicamba volatility. BASF has formulated dicamba as a heavy (high molecular weight) BAPMA (Bis(3-aminopropyl)methylamine)) salt that is much heavier than the dma or dga salt of Banvel and Clarity. The heavy salt greatly reduces the capacity for the dicamba active ingredient to move after application. Monsanto used the VaporGrip technology which the active ingredient(s) has not been released at least to academia. We surmise the VaporGrip acts as a buffer to keep the spray solution pH above 5.5 or above that range. That is why acidifiers are not allowed.

When dicamba reacts with spray water above 5.5 pH it forms the anionic form of dicamba which has a low vapor potential. At water pH below 5.5 the dicamba will convert to the acid form, which has very high vapor potential. That is most important and why industry recommendations are used to keep dicamba from converting into the acid form. AMS can influence water pH causing the pH to acidify which can cause the dicamba to convert to the acid form. Also, (excuse a personal example) when my wife gives me a bottle of ammonia and tells me to go clean the shower it does not take long before the volatile ammonia begins to burn my lungs. Ammonia is volatile which could increase the volatility of dicamba. AMS contains ammonium but ammonium can lose a proton in water to convert into ammonia, which will yield the same high volatility results.

ND growers are the most advanced and loyal in AMS use of all growers in the U.S. Most have responded positively to NDSU research and recommendations to use AMS not only with glyphosate but with all weak acid (most POST) herbicides. The sulfate precipitates the hard water minerals and the ammonium binds with the weak acid herbicide increasing absorption and drives the proton pump inside plants resulting in greater herbicide translocation and efficacy. AMS should NOT be used in ANY form in DT soybean. Even though the cost of AMS replacement adjuvants is significantly higher than AMS only those adjuvants on the respective chemical company web sites are allowed to be added with dicamba. To help growers with adjuvant selection the weed guide has been revised to show adjuvants that contain AMS are on page 127 and those adjuvants that do not contain AMS are on page 128.

 

Rich Zollinger

Extension Weed Specialist

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