Don’t forget AMS with glyphosate
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
There are over 280 products (commercial and ready-to-use) with glyphosate currently registered for use in Michigan. One of the main differences among the many available products is the surfactant component of the formulated products; some may need additional surfactant while others do not (See Table 10, p. 132 in the 2006 Weed Control Guide for Field Crops, E-434 for a listing of the commercial products used in agriculture). However, ammonium sulfate (AMS) should always be added to all glyphosate products in order to minimize the negative effect of hard water on glyphosate activity. If AMS is not used, calcium and magnesium ions found in hard water will bind to the glyphosate molecules and reduce the efficacy of the glyphosate treatment. It is important to add the AMS to the spray mixture first to prevent the hard water ions from attaching to the glyphosate.
The addition of AMS also can improve glyphosate’s efficacy on some species, especially velvetleaf, regardless of water quality. Dry AMS should be labeled “spray grade” quality and applied at 17 lbs/100 gal. Liquid AMS products are equally effective if applied at a rate equivalent to 17 lbs/100 gal.
There are also many AMS substitutes on the market. These products typically contain varying amounts of AMS. When added according to the product instructions, the actual amount of AMS in many of these substitutes is less than 17 lbs/100 gal. MSU has tested some, but certainly not all, of the current commercial products. This research has shown that the most effective AMS substitutes are those that contain the highest amount of AMS. Some AMS substitutes were ineffective at overcoming antagonism from the hard water and none of the products tested at MSU were superior to the standard recommendation of 17 lbs/100 gal of AMS.
Recommendation: Always use AMS at 17lbs/100 gal. with all glyphosate products, and add the AMS to the spray mixture before the glyphosate to prevent antagonism from hard water.