No. 10 Article 5/June 2, 2006

How Much Product to Add in Handheld Sprayers?

Most folks who consult the Bulletin and apply pesticides do so most commonly across large acreages using field-scale application equipment. Pesticide labels indicate application rates in a variety of ways, the most common being amount of formulated product (fluid ounces, pints, quarts, ounces, or pounds) per acre. Determining the amount of product to add to the tank is easily calculated from knowing the volume of carrier to be added to the tank and the number of acres treated per load. Sometimes, however, individuals would like to know how much formulated product to add to smaller-scale application equipment, such as a handheld sprayer or perhaps a spray system mounted on an all-terrain vehicle. Again, the product label is the place to start.

If a particular herbicide is labeled for application via handheld or other smaller-scale equipment, the label may indicate application rates in several different ways. Some product labels will specify how many fluid ounces of product to add for a 1-gallon sprayer, a 2-gallon sprayer, and so on. These rates sometimes depend on what type or types of plants you are attempting to control (woody perennials vs. annual grasses, for example). Other labels may indicate application rates as a specific spray concentration, such as a 1% spray solution. So, how much product would be added to a 2-gallon handheld sprayer if the label specified a 0.5% spray concentration?

First, we'll assume most people will be working with liquid products and measuring in English units, so the text here uses units of fluid ounces and gallons (metric equivalents are presented in Table 1). Returning to our example, first convert 2 gallons to fluid ounces: 128 fluid ounces per gallon x 2 gallons = 256 fluid ounces in 2 gallons. Next, simply multiply the desired spray concentration by the number of fluid ounces you wish to mix: 0.005 x 256 fluid ounces = 1.28 fluid ounces of product. In this example, the applicator will need to add 1.28 fluid ounces of the formulated herbicide to 2 gallons of water to achieve a 0.5% spray solution.

Table 1 provides a quick reference for the amount of formulated herbicide needed (some rounding was done) to achieve various spray concentrations based on the number of gallons mixed. The table lists these amounts three ways: as fluid ounces, milliliters, and teaspoons/tablespoons. Conversions and a few sample calculations also are included.--Aaron Hager

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