No. 2 Article 11/April 1, 2004

Corn and Soybean Herbicide Premixes

Herbicide premixes can often be confusing with respect to components, product equivalents, application rates, and so on. Table 3 lists many of the corn herbicide premixes used in Illinois, while Table 4 is a similar list of soybean herbicide premixes. Let's examine the information in these tables in a little more detail.

The first column lists the commercial, or trade, name of the herbicide and its formulation. The trade name is the one most familiar to folks. Another list of names (arguably less familiar than the trade names) appears in column 2; these are the common names for each herbicide component of a premix. For example, in Table 3, we see that Axiom (trade name) 68DF (formulation) is composed of the active ingredients flufenacet (common name) and metribuzin (common name). Common names are useful because they always refer to the same active ingredient; trade names don't always. Think back a few 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, you do not want to apply fenoxaprop to corn or foramsulfuron to soybeans--hence the benefit of knowing herbicide common names. Column 2 also provides the amount of active ingredient or acid equivalent of each component per gallon or pound of formulated product.

Column 3 lists an application rate for each premix. We tried 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. Column 4 indicates how much of each active ingredient is applied at the rate listed in column 3. Going back to the example of Axiom, we see that 19 ounces of Axiom provides 0.646 lb flufenacet active ingredient and 0.162 lb metribuzin active ingredient. Note here 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 units of pounds of active ingredient or acid equivalent per acre.

Finally, the last column lists product equivalents for each premix component when applied at the rate listed in column 3. So the 19-ounce rate of Axiom provides the same amount of flufenacet and metribuzin that is contained in 17.23 ounces of Define 60DF and 3.45 ounces of Sencor 75DF, respectively.

The application rates in the tables are meant to be used for reference; for some of these herbicides application rates will vary depending on soil texture, organic matter, weed species size, and other factors. 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.

The application rate of Harness Xtra 5.6L listed in 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:

2 quarts/acre x 1 gallon/4 quarts = 0.5 gallon

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

0.5 gallon/acre x 3.1 lb ai acetochlor/gallon = 1.55 lb ai acetochlor per acre

0.5 gallon/acre x 2.5 ai atrazine/gallon = 1.25 lb ai atrazine per acre

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

1.55 lb ai acetochlor/acre x 1 gallon Harness/7 lb ai x 8 pints/gallon = 1.77 pints Harness 7E

1.25 lb ai atrazine/acre x 1 gallon AAtrex/4 lb ai x 8 pints/gallon = 2.5 pints AAtrex 4L

--Aaron Hager and Dawn Nordby

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