Cross post from UC Weed Science blog 12/20/17 Glyphosate is one of the most widely used herbicides in the world and is extremely important in many of our orchard, vineyard, and annual crops as well as in non-crop and home situations. However, it can be confusing to understand some of the differences among various formulations of glyphosate herbicides. I’ll paraphrase a recurring extension question like this: “I’m trying to compare the rates and cost-effectiveness of two glyphosate herbicides. One lists the active ingredient as ‘41% glyphosate as the isopropylamine salt’ and the other as 48.7% glyphosate as the potassium salt’.  How do I compare these two herbicides?” First important point, glyphosate is a weak acid herbicide.  The various salt formulations have major impacts on how the herbicide behaves in the jug, and to some degree on how it gets into the plant.  But once in the plant, it is the glyphosate acid that binds to the target enzyme in susceptible plants and causes the herbicidal effect. What is a salt? From a chemistry perspective, a salt is simply a compound formed by ionic bonding of two ions of opposite charge.  Glyphosate acid has a weak negative charge and the salt is formed when the glyphosate acid is bound to a base that has a positive charge.  In the cartoon below, this is illustrated a little incorrectly – you can see the negatively charged glyphosate acid on the left (C3H8NO5P); however, the “salt+” tagged on the right should really be labeled  “base+” (the combined molecule is actually the “salt”).   (image from www.wheatgrowers.com)  ((the “salt” on the right should more accurately be labeled “base”)) What are some common glyphosate salts? There are several glyphosate salts currently available in the market and others have been in the past but are less common now.  Four examples (below) include:

Over the past few years, herbicides with the active ingredient glufosinate (Rely, Rely 200, Rely 280) have become very important in California almonds as well as other tree nuts and grape vineyards. Glufosinate is classified as a “Group 10, or Group B” herbicide an inhibits an enzyme important in the production of the amino acids glutamine in plants.  Although it sounds similar to another amino acid inhibitor, glyhosate (the active in Roundup and others) glufosinate works quite differently than the Group 9 herbicide glyphosate.  Click here for more mode of action information from WSSA.