The percentage of the active ingredient that you see on any pesticide label represents the percentage BY WEIGHT of that active ingredient in that formulation. So, for dry concentrates it's pretty easy to figure this out. If we pick a few examples of products we can first pick Tempo Ultra WP, which is 10% active ingredient by weight in the package. This means that in a 14.8 ounce jar of the product there will be 1.48 ounces of active ingredient - just divide the total weight by 10. Now, we do get confusion when we try to mix Metric with our normal standards of ounces and pounds, as so many product labels now use metric. The Tempo label is no exception, as it allows you to use either 10 grams or 20 grams of the concentrate powder in 1 gallon of water. Frankly, for purposes of your pesticide use report I think you would be fine just reporting the use in grams, and since for this example in 10 grams of Tempo Ultra WP you have 1 gram of active ingredient you know that mixing that low rate in a 1 gallon tank and applying it means you applied 1 gram of active ingredient.
If you are determined to keep everything in ounces and pounds you just have to do a little math. Or, just take the easy way out like I do and "Google" it on the internet - just put "1 gram equals ounces" and your answer will pop right up. But, 1 ounce equals 28.35 grams, so if you prefer the old fashioned way you would just divide 1 by 28.35 to come up with 0.035 ounce of active ingredient when you place 1 scoop (10 grams) of the concentrate powder in 1 gallon of water. These kinds of conversion charts and examples of the math can be found on PestWeb as well, in our Pest ID and Weed ID resources.
For ready to use formulations such as dusts or granules the same principal applies. Thus, in Demand G granules there is 0.045% active ingredient (lambda cyhalothrin), meaning for each 100 pounds of the granules you use you have applied less than 1/50th of a pound of active ingredient. What's really nice on this particular product's label is that it already tells you how much a.i. you use! For 2 lbs of product you use 0.04 lbs of active ingredient. If we want to convert that to ounces we just multiply by 16 (1 lb equals 16 ouunces), so 0.04 lbs = 0.64 ounces of a.i., and that may be spread over 1000 square feet according to the label - very little actual active ingredient used.
For liquid concentrates it gets a little trickier, but the principal is the same. One gallon of liquid (water) weighs 8.34 pounds. So, in a product called Termidor SC we find 9.1% concentrate. Since the total weight of that gallon is about 8.5 pounds we just multiply 8.5 times 0.091 (remember basic math regarding converting a % to a fraction?) and come up with 0.77 lbs of active ingredient. Convert that to ounces of active ingredient as 0.77 X 16 = 12.3 ounces of fipronil in a 1 gallon jug of Termidor.
For General Pest uses the low rate on the label calls for mixing 0.8 ounces of concentrate in 1 gallon of water. What fraction of 128 ounces (1 gallon) is that 0.8 ounces that you use in 1 gallon? Well, 0.8 divided by 128 = 0.006, and you multiply this times the 12.3 ounces of a.i. in a gallon of concentrate to come up with just 0.07 ounces of active ingredient used in 1 gallon of water.
I know this can be really confusing because of the VERY low rates of use we now have with our current insecticides. It used to be a lot easier when we used 1% concentrations of chlordane or diazinon, but the math can be simple once you do it a few times.
Mr. Pest Control
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Please note, Mr. Pest Control is answering questions supplied by PMP customers across North America. His answers are generated from industry and manufacturer-provided information. The answer may not be specific to the laws and regulations for your State, Province, Territory or Country. In addition, products mentioned may not be registered and or available in all areas. Always check with your local Univar office for specific information to your area. Always read and follow label directions.