I have heard some of our agronomists and staff talking a lot about different glyphosate offerings for 2016. It seems that every generic supplier out there has their version of glyphosate to sell. There are different “types” of glyphosate on the market- different salts of the glyphosate base acid, as well as different analyses of the content of glyphosate in the jug- anywhere from 4 lb product to what is called 6 lb product. You can see marketing programs stating things like “Acid Equivalent” and claims/statements on “Active Ingredient”. There are also differences in formulations from brand name suppliers and some generics. This is enough to be thoroughly confusing, and I seem to think some suppliers want it that way. The key is to be sure to compare “apples to apples”, if you will. Here are few comments to sort out the mess.
Glyphosate Formulations- Salts
Glyphosate has been used since it was initially registered in 1974. It kills plants by inhibiting a specific enzyme in plants- the EPSP enzyme, disrupting amino acid production. Glyphosate is sold as a formulated SALT- the negative charged glyphosate molecule complexed with a positive charged portion forming a salt of some sort. Common salts are potassium, diammonium, isopropylamine, trimethylsulfonium (trimesium) and sesquisodium.
Formulations differ in how much glyphosate molecule is in the formulation, because the salts vary in weight significantly. This is partially why we get anywhere from 4- 6 lb of active ingredients per gallon in the jug. See the attached chart for the content of formulated glyphosate salt in a gallon of formulated product. The amount of salt per gallon of product is called an ACTIVE INGREDIENT listing.
Why Glyphosates Salts?
Glyphosate salts are better able to enter the plant tissue than glyphosate acid. Only the active glyphosate portion of the molecule is herbicidal- the salt is non-herbicidal.
ACID EQUIVALENTS vs. ACTIVE INGREDIENTS
Different salts of glyphosate have different molecular weights. Therefore different concentrated salt solutions can have very different amounts of the actual active glyphosate molecule in the blend. ACTIVE INGREDIENT (A.I.) listings list the amount of Glyphosate Salt per gallon. However to make a fair comparison of weed killing ability, the ACID EQUIVALENT (A.E.) is the number that represents the amount of Actual Glyphosate Molecule per gallon of product. Comparing acid equivalents get to the real weed killing power of a formulation, and may be a more fair “apples to apples” comparison.
What Else Is In The Jug?
Adjuvants are products mixed with formulated herbicides to improve performance by improving spread on the leaf, uptake into the leaf, etc. Glyphosate formulations that are called “fully loaded” have a built-in compliment of adjuvant in the formulation. This is usually a cationic (positive charged) surfactant, and may be enough on its own for effective use. Additional non-ionic surfactant (NIS) is often added at application to improve performance when weed pressure is high or weeds have thick cuticles.
Solvents And Emulsifiers
Pesticide products vary in the solvents used to dissolve the salts and organic molecules of the active ingredient pesticides or emulsifiers to make an oily base compound mixable with water. Brand name companies have consistent solvent supplies and have fully vetted their solvent systems in spray mixes. Generic suppliers may use less expensive solvents or may vary their solvent blend lot to lot, which can have extreme impacts on the storage, handling and mixing of the formulated products. The best option is to use well-known products to reduce potential handling issues. Solvent choice also affects handler safety and the SIGNAL WORD needed on the label.
Why Do We Add AMS To Glyphosate?
When glyphosate is in solution, the “salt” partially separates, forming negative charged glyphosate acid and positive charged salt ions in solution. This leaves the glyphosate exposed to chemical reactions in the water. If the water we spray with has a large concentration of cations (+ charge) like calcium or magnesium, these molecules bind tightly to the glyphosate acid, reducing the effectiveness of the product. Ammonium sulfate is a salt in and of itself. In water, it splits into two positive charged ammonium ions (NH4+) and one negative sulfate ion
(SO4-2). This helps two ways- glyphosate acid bound to an ammonium ion is highly absorbed by plants, plus the sulfate binds well to calcium and magnesium ions, keeping them away from the glyphosate.
Glyphosate Product Choices
SDWG offers a wide range of glyphosate products for growers- brand name and well-known, proven “generic” brands. Use of these vetted brands will offer the best opportunity for solid weed control performance and ease of handling throughout the season.