Determining the correct amount of herbicide to mix with water is often confusing, leading to either ineffective weed control or damage to desirable plants. Manufacturers provide application rates in various units, such as ounces per acre or a percentage solution per gallon. Accurately translating these label instructions into a precise measurement is crucial for product efficacy, environmental protection, and applicator safety. Miscalculation can result in over-application, causing plant injury, or under-application, which fails to eliminate target weeds.
Decoding the Herbicide Label
The herbicide product label is the single most authoritative and legally binding guide for use. It contains all the specific parameters required for proper mixing and application. The first information to locate is the Active Ingredient and its concentration percentage, which indicates the product’s strength.
Liquid concentrates often list strength as a percentage (e.g., 41% glyphosate) or in pounds of active ingredient per gallon. The Target Application Rate is also necessary. This rate specifies the amount of commercial product needed to treat a specific area, typically expressed as ounces or pints per acre or per 1,000 square feet.
Calculating Spot Treatment Dilutions
Spot treatments use hand-held or backpack sprayers for targeted applications, and the mixing rate is concentration-based, not area-based. The label usually provides a specific dilution ratio, often stated as a percentage solution or fluid ounces per gallon of water. If the label recommends a percentage solution, such as a 2% mix, the goal is to determine the volume of concentrate needed to make one gallon of the final solution.
The simplest calculation uses the conversion of 128 ounces per gallon. For a 2% solution, multiply 128 oz. by the decimal equivalent (0.02), yielding 2.56 fluid ounces of concentrate per gallon. Since one fluid ounce equals two tablespoons, a 2% solution requires approximately five tablespoons of concentrate. This concentrate must be mixed with enough water to reach a total volume of one gallon, not added to a full gallon of water, to maintain the correct final concentration.
Calculating Broad Application Dilutions
Broad application dilutions, typically for treating an entire lawn or field, are complex because they are based on area coverage, not just a simple concentration ratio. The goal is to ensure the correct amount of herbicide is dispersed evenly over the target area, regardless of the sprayer’s tank size or water volume used. The process starts by determining how many acres or thousands of square feet a full tank of mixed solution will cover.
This requires knowing your sprayer’s output, measured in Gallons Per Acre (GPA) or Gallons per 1,000 square feet, which is found through calibration. The acres covered per tank is calculated by dividing the sprayer’s tank capacity by the calibrated GPA output. For example, if a 15-gallon sprayer applies 30 GPA, one full tank covers 0.5 acres (15 gallons / 30 GPA = 0.5 acres).
The next step is calculating the precise amount of concentrate to add to the tank. Multiply the acres covered per tank by the label’s recommended herbicide rate per acre. If the label calls for 3 pints per acre, and your tank covers 0.5 acres, you would add 1.5 pints of concentrate (0.5 acres \(\times\) 3 pints/acre). This method ensures the correct dosage is applied to the land, using water only as a carrier for uniform delivery.
Safe Mixing and Handling Procedures
Mixing herbicides requires strict adherence to safety guidelines to minimize applicator exposure. Proper Personal Protective Equipment (PPE) is mandatory, and the label specifies the necessary gear. This commonly includes:
- Chemical-resistant gloves.
- Protective eyewear.
- Long sleeves and long pants.
Work in a well-ventilated area away from people and pets.
The sequence of adding materials to the spray tank is important for ensuring a uniform solution. Generally, fill the tank halfway with clean water first, followed by continuous agitation. Slowly add the concentrated herbicide, allowing it to mix thoroughly before adding any required additives like surfactants. Finally, add the remaining water to reach the total desired volume, maintaining agitation throughout the process. Measuring containers must be triple-rinsed, with the rinse water poured directly into the spray tank.