Maintenance: Equipment Calibration

Recommended application rates of commonly used herbicides can at times be difficult to understand. In the product label, most herbicide manufacturer’s state recommended rates for target species in “ounces per acre” language. For most weekend weed warriors, these instructions can be confusing when trying to mix concentrated herbicide with water to eliminate the noxious weed of choice. Through the calibration of your sprayer, this process is simplified. Moreover, calibration of your sprayer is important for both environmental and economic reasons.Every sprayer that is manufactured can vary in output due to pressure and nozzle setting, as well as applicator technique. Through the calibration process, output is measured to produce a “gallons per acre” figure. With the use of sprayer output in gallons per acre, a mix rate of ounces per gallon is easily obtained. While most noxious weed infestations in Teton County do not require treatment of an entire acre, this knowledge is essential to certify that the proper amount of herbicide is mixed with water in your specific piece of equipment. There are many different types of calibration methods that can be used. If you are using a backpack sprayer, or using any type of handgun sprayer, one method would be to use the 1/128th method. This is where you measure out an area that is approximately 1/128th of an acre (a square of 18.5’ x 18.5’ works well) and timing yourself while you uniformly cover spray (using water only) that area. Repeat this 3 or 4 times, and then take the average time and spray in to a bucket for that average time, making sure to keep your pressure the same as when you were spraying. Once you have completed this, measure the amount of water in ounces. Since there are 128 ounces in a gallon, there is a direct ratio with 1/128th of an acre, so however many ounces you collect will equal your gallons per acre. For example, let’s say you spray an area 18.5 ft by 18.5 ft. It takes you on average 45 seconds to complete this. You then spray in to a bucket, or other large container, for the 45 seconds. In that 45 seconds you collect 40 ounces of water. You are then calibrated at 40 gallons per acre.By calibrating your equipment, you are ensuring that the proper amount of herbicide is being delivered to the target species to produce the desired effects. Under-application may not deliver enough herbicide to the plant to provide a lethal dose, and can contribute to herbicide resistance in plant communities. Some environmentally sensitive applicators may choose to reduce the recommended rates of application in order to reduce the potential for perceived negative environmental effects. However, the opposite may be true. By providing a less than lethal dose of herbicide, the target species may continue to flourish, while also building up resistance to the herbicide that it was exposed to.Furthermore, by correctly applying the recommended rate of herbicide, it is possible to increase economic efficiency. Incorrect rates of application of herbicide to plants may not kill the targeted plant fully, or might just kill off the above-ground portion while allowing the roots to survive and send up additional growth. By delivering the recommended amount of herbicide, both situations can be avoided. Money is saved in both herbicide (over application) and labor (re-treatment) costs.You should be calibrating your equipment at a minimum of once a year. This is important because certain parts in the sprayer may begin to wear over time, causing a change in output. The way that you spray may also change from year to year, which could affect the calibration. You should also recalibrate your equipment any time you repair or replace a part. This too can cause a change in the flow of the sprayer, even though it might seem like a small change. If you need assistance in calibrating your equipment, please do not hesitate to contact Teton County Weed and Pest at 307-733-8419. We will be happy to answer any of your questions, and if you bring your sprayer to our office we will even help you calibrate. You can also visit our website https://tcweed.org/resources/videos/ for a couple of videos that help explain how to calibrate.