Spot treatments call for care and calibration

Something went wrong. Please try again later...
spot spray treatment

Catching new weed infestations early is a smart, economical and convenient way to maintain grazing lands.

Spot-spraying weeds is especially popular during the summer months, when managing new threats from noxious and invasive species — from knapweeds to thistles.

But treating relatively small areas and applying lesser amounts of product still requires responsible, proper application. Often it also requires a more complex answer to a simple question. For example:

Q. How much Product X do I put in my 2-gallon hand sprayer?

A (or another question, in this case). How much spray volume are you applying with your spray equipment and individual spraying style?

Don’t have an answer? Here’s a simple step-by-step procedure to determine your individual spray volume and then how much product — DuraCor® herbicide in this example — to add to your sprayer:

Step 1: Clean your sprayer and nozzle thoroughly. Then fill the spray tank with clean water. Spraying with water only, make sure the nozzle forms a uniform spray pattern.

Step 2: Measure an area 18.5 feet by 18.5 feet, which equals 1/128 of an acre. If possible, this should be done in the area where you will be spraying.

Step 3: Time the number of seconds it takes to spray the measured area uniformly with water by using a side-to-side sweeping motion with the spray wand. Think of it as spray-painting the measured area. Record the number of seconds required to spray the area. During application, be sure to maintain a constant sprayer pressure. It will take about four to six passes through the area for complete coverage, and you should repeat this step at least twice, making sure the results are consistent to calculate an average time.

Step 4: Spray into a container while maintaining constant pressure for the average time calculated in Step 3.

Step 5: Measure the number of fluid ounces of water in the bucket. This amount is equal to the number of gallons per acre (gpa) of water the sprayer is delivering.

Step 6: Use the accompanying table to determine how much DuraCor to add to 2 gallons of water. Find your spray volume in gpa (calculated above) and read across the chart to determine the amount of DuraCor to use based on the desired application rate.

Best of all, this method works whether you’re using a small pump-up sprayer, a backpack sprayer or an ATV rig outfitted with a hand wand.


You have completed the calibration procedure and applied 40 fluid ounces in the measured area. Thus, with your individual spraying style, you can expect to apply a spray volume of 40 gpa. Now, you’ve determined you want to apply the 20-ounce-per-acre rate of DuraCor. Referencing the table, the amount of DuraCor herbicide needed for your gpa is 1 fluid ounce. Add 1 fluid ounce of DuraCor into 2 gallons of water plus 2 tablespoons of a quality agricultural surfactant. Shake the sprayer to make sure DuraCor is in solution.

Tips for accurate measuring: DuraCor is a low-use-rate herbicide. As the table illustrates, higher gpa applications require a relatively small amount of product. A disposable syringe calibrated in milliliters (available at veterinary supply and farm supply stores) is an excellent option. It allows you to accurately measure small amounts (for example, 0.2 fluid ounce equals 6 milliliters). Another advantage is you can draw the herbicide into the syringe directly from the product container, helping to prevent spills on your hands or clothes. You can find online calculators to help convert fluid ounces to milliliters.      

Amount of DuraCor® Herbicide (in Fluid Ounces) to Mix in 2 Gallons of Water

Water Volume Applied
in Gallons per Acre
Desired Application Rate of DuraCor Herbicide
12 fl. oz./A 16 fl. oz./A 20 fl. oz./A
20 gpa 1.2 1.6 2.0
40 gpa 0.6 0.8 1.0
60 gpa 0.4 0.5 0.6
80 gpa 0.3 0.4 0.5
100 gpa 0.2 0.3 0.4


® Trademark of Corteva Agriscience and its affiliated companies. Under normal field conditions, DuraCor® is nonvolatile. DuraCor has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. Label precautions apply to forage treated with DuraCor and to manure and urine from animals that have consumed treated forage. DuraCor is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Consult the label for full details. Always read and follow label directions.

Stay Connected With Us

Connect with Range & Pasture:


Find Your Local R&P Specialist

Range & Pasture Steward Newsletter

Learn about seasonal opportunities, rancher success stories, and management strategies for pastures and rangeland.

Explore Articles

Subscribe to Steward