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Issue No. 4, Article 8/April 21, 2006

What's in That Premix?

It's no great revelation that the introduction of novel herbicide active ingredients has slowed recently but that at the same time a plethora of premix products has proliferated. For the past several years, we have published an article in the Bulletin that describes herbicide premix products commercially available for corn and soybean production, and we continue that tradition this year. The basic text hasn't changed much over time, and we hope it remains useful. Updated tables of corn and soybean premixes always accompany this article and are described in detail in the following text. One limitation of the 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 from the one presented, the text provides examples for doing the calculations.

Herbicide premixes often can be confusing with respect to component active ingredients, product equivalents, application rates, and so on. Table 4 lists many of the corn herbicide premixes used in Illinois, while Table 5 is a similar list of soybean herbicide premixes. Let's examine the information in these 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 one usually more 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 4 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 soybeanhence 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 tried to select rates representative for Illinois, but you may want to choose a different rate and redo the calculations in the fourth and fifth columns. The fourth column indicates how much of each active ingredient is applied at the rate listed in the third column. Using 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, quarts, and so on of product per acre, active ingredients are usually expressed in pounds of active ingredient or acid equivalent per acre.

Finally, the last column lists product equivalents for each premix component when the premix is applied at the rate listed in the third column. 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 listed in the tables are meant to be used as a reference; for some of these herbicides application rates will vary with soil texture, organic matter, weed species and size, and so on. Always consult the respective herbicide label for appropriate application rates. If you are interested in a rate different from 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 listed in Table 4 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, calculate how much acetochlor and atrazine active ingredient are contained in 0.5 gallon of Harness Xtra 5.6L:

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

--Aaron Hager and Dawn Nordby

Aaron Hager
Dawn Refsell

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