Unless a person deals with these types of calculations frequently, they may be a challenge. With this article, I will demonstrate how you can make these types of conversions and the information that you need.
Herbicide Product Conversions
Chris Boerboom, Extension Weed Scientist
I received a couple good questions about herbicide rate conversions lately. One example was calculating how much Pursuit and Prowl H2O should be mixed to equal the Pursuit Plus (which is no longer being manufactured). Unless a person deals with these types of calculations frequently, they may be a challenge. With this article, I will demonstrate how you can make these types of conversions and the information that you need.
First, if you are interested in knowing the general composition of some of the common corn and soybean herbicide premixtures, there are two handy tables in the Pest Management in Wisconsin Field Crops bulletin, A3646. In the 2009 edition, check out these tables.
Rate equivalents of corn herbicide premixes – page 53
Rate equivalents for soybean herbicide premixes – page 120
While the rate you are using might differ from the rates listed in these tables, they will give you a good understanding of the ratio of the components. For instance, 2.4 oz of Gangster is equivalent to 2 oz of Valor and 0.4 oz of FirstRate.
However, the information in these tables does not answer the original question of how much Pursuit and Prowl H2O to mix to equal 2.5 pt/a Pursuit Plus. For these types of questions, we need to deconstruct the original herbicide down to its active ingredients and then reconstruct it into the herbicides of interest. I will use an example to show how this is done.
Step 1. Find amount of Pursuit in 2.5 pt/a Pursuit Plus
- Check Pursuit Plus label (or Table 1a, p. 227 in A3646 bulletin) to find concentration of imazethapyr, which is 0.2 lb/gal.
- Convert Pursuit Plus use rate to gallon rate >>>
2.5 pt/a Pursuit Plus ÷ 8 pt/gal = 0.3125 gal Pursuit Plus/a
- Determine amount of active ingredient in use rate (this is the deconstruction) >>>
0.3125 gal/a × 0.2 lb imazethapyr/gal = 0.0625 lb imazethapyr/a
- Check Pursuit label (or Table 1a, p.227 in A3646) to find concentration of imazethapyr, which is 2 lb/gal to convert back to Pursuit (start reconstructing).
- Determine gallons of Pursuit needed to provide a 0.0625 lb rate of imazethapyr. >>>
0.0625 lb imazethapyr/a ÷ 2 lb imazethapyr/gal = 0.03125 gal Pursuit/a
- Convert gallons of Pursuit to ounces. >>>
0.03125 gal/a × 128 oz/gal = 4 oz/a of Pursuit
Step 2. Repeat to find amount of Prowl H2O in 2.5 pt/a Pursuit Plus (I’ll just do the calculations using the same steps as above).
2.5 pt/a Pursuit Plus ÷ 8 pt/gal = 0.3125 gal Pursuit Plus/a
0.3125 gal/a × 2.7 lb pendimethalin/gal = 0.8438 lb pendimethalin/a
0.8438 lb pendimethalin/a ÷ 3.8 lb pendimethalin/gal = 0.222 gal Prowl H2O/a
0.222 gal/a × 8 pt/gal = 1.78 pt/a of Prowl H2O
The answer is 2.5 pt/a Pursuit Plus = 4 oz/a Pursuit + 1.8 pt/a Prowl H2O
Similar calculations can be used to determine the rate equivalents of other products or to convert from one formulation to another. For example, how much of Nufarm’s 2,4-D LV6 would it take to equal a 1 pt/a rate of Nufarm’s 2,4-D LV4?
1 pt/a LV4 ÷ 8 pt/gal = 0.125 gal LV4/a
0.125 gal LV4/a × 3.84 lb 2,4-D/gal (in the LV4) = 0.48 lb 2,4-D/a
0.48 lb 2,4-D/a ÷ 5.5 lb 2,4-D/gal (in the LV6) = 0.0873 gal/a LV6
0.0873 gal/a × 8 pt/gal = 0.7 pt/a of LV6
For a practice problem, calculate the amount of Touchdown Total that would be equivalent to the glyphosate rate in 4 pt/a of Halex GT. For hints, Halex GT has 2.09 lb glyphosate/gal and Touchdown Total has 4.17 lb glyphosate/gal. Is the correct amount?
a. 22 oz/a Touchdown Total
b. 24 oz/a Touchdown Total
c. 32 oz/a Touchdown Total
d. 36 oz/a Touchdown Total
e. I need more practice, but I can always come back and follow these examples.