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Issue No. 5, Article 4/April 25, 2008

What's in That Herbicide Premix?

Though the introduction of novel herbicide active ingredients has slowed during the past several years, a plethora of premix products has proliferated. In the past we have published an article in the Bulletin describing herbicide premix products commercially available for corn and soybean production, and we continue that practice this year. The basic text hasn't changed much over time, and we hope it remains useful to our readers. Updated tables of corn and soybean premixes always accompany the article; they are detailed in the following text. One limitation of these tables is that a single application rate of each product is presented, with product active ingredients and equivalents calculated based on that rate. If you would like to determine product active ingredients and equivalents for a rate different than the one presented, we provide examples of how to do the calculations.

Herbicide premixes can be confusing with respect to component active ingredients, product equivalents, application rates, and the like. Table 3 lists many of the corn herbicide premixes used in Illinois, and Table 4 is a similar list of soybean herbicide premixes. Let's examine the information in the tables in more detail.

The first column lists the commercial or trade name of the herbicide and its formulation. The commercial or trade name is the name usually most familiar to folks. Another list of names (arguably less familiar than the names in the first column) appears in the second column; these are the common names for each herbicide component of a premix. For example, in Table 3 we see that Lexar (trade name) 3.7L (formulation) is composed of the active ingredients S-metolachlor (common name), mesotrione (common name), and atrazine (common name). Common names are useful because they always refer to the same active ingredient; trade names don't always refer to the same active ingredient. Think back several years to a herbicide with the trade name Option; this product contained the active ingredient fenoxaprop (common name) and was used for postemergence control of grass species in soybean. The Option (trade name) herbicide now on the market contains foramsulfuron (common name) and is used for postemergence control of grass species in corn. Needless to say one does not want to apply fenoxaprop to corn or foramsulfuron to soybean--hence the benefit of knowing herbicide common names. The second column also provides the amount of active ingredient or acid equivalent of each component per gallon or pound of formulated product.

The third column lists an application rate for each premix. We attempt to select application rates representative for Illinois, but you may want to select a different rate and redo the calculations in columns 4 and 5. The fourth column indicates how much of each active ingredient is applied at the rate listed in the third column. Going back to the example of Lexar, we see that 3.5 quarts of Lexar provides 1.52 lb S-metolachlor active ingredient, 0.196 lb mesotrione active ingredient, and 1.52 lb atrazine active ingredient. Note that while rates of commercial products are usually expressed in ounces, pounds, pints, or quarts of product per acre, active ingredients are usually expressed in units of pounds of active ingredient or acid equivalent per acre.

Finally, column 5 lists product equivalents for each premix component when the premix is applied at the rate listed in column 3. So the 3.5-quart rate of Lexar provides the same amount of S-metolachlor, mesotrione, and atrazine contained in 1.6 pints of Dual II Magnum 7.64EC, 6.27 fluid ounces of Callisto 4SC, and 3 pints of AAtrex 4L, respectively.

The application rates in the tables are meant to be used as a reference; for some of these herbicides the rates will vary depending on soil texture, organic matter, weed species and size, and other factors. Always consult the respective herbicide label for appropriate application rates. If you are interested in a rate different than that listed for a particular herbicide, it's relatively simple to do the calculations for your rate of choice. We'll work through an example to make it a little easier to understand.

The application rate of Harness Xtra 5.6L (Table 3) is 2.5 quarts per acre. Instead of 2.5 quarts, you want to know how much acetochlor and atrazine are applied at a 2-quart rate of Harness Xtra 5.6L.

First, convert 2 quarts to gallons:

Next, we can calculate how much acetochlor and atrazine active ingredient are contained in 0.5 gallon of Harness Xtra 5.6L:

Finally, we can determine product equivalents based on these active ingredient amounts:

--Aaron Hager

Aaron Hager

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