An item in the October, 2003, issue on the proper order of tankmixing glyphosate products led to a comment from a No-Till Farmer reader in North Dakota. He informed us that research conducted at North Dakota State indicates that the efficacy of Roundup herbicide is not affected by the order in which it is mixed with water and ammonium sulfate (AMS).

His comments were based on a Page 5 item from Bryan Young at Southern Illinois University that stated that tankmixed ingredients should be added in a particular order to achieve full effectiveness of the tankmix. Young says adding AMS to a tankmix will significantly increase weed control, providing it is the first ingredient that is added. The reason, says Young, is that glyphosate is an acid and thus has a negative charge in the tank and can react unfavorably with hard water and reduce the effectiveness of the herbicide due to slower absorption.

On the other hand, each AMS molecule contains two positively charged ammonium ions and one sulfate ion with a negative 2 charge. When AMS is placed in the tank followed by water, he says the negative 2 sulfate will bind to the positively charged ions found in the water and prevent the formation of calcium glyphosate.

Theory One

North Dakota State University weed scientist Rich Zollinger says there are two schools of thought regarding the proper mixing order when glyphosate products are part of your tankmix. He says research data from Michigan State University supports the…