Atrazine is a selective herbicide used to control broadleaf and grassy weeds in agricultural crops like corn and sorghum, and in certain turfgrass applications. This chemical functions by disrupting photosynthesis in susceptible plants, providing both pre-emergent and post-emergent control of weeds. Determining the correct mixing ratio for a small application requires a precise calculation based on the area being treated, not simply the volume of water in the tank. The most important step for any user is to strictly follow the specific instructions provided on the product label, as application rates and restrictions vary significantly.
Understanding Atrazine Formulations
There is no single “atrazine per gallon” rate because the herbicide is sold in different concentrations, which dictates how much product is needed. The two most common forms are Liquid Concentrate and Dry Flowable.
Liquid Concentrate
Liquid Concentrate formulations, often designated as “4L,” contain four pounds of atrazine active ingredient (ai) per gallon of product. This liquid formulation is easily measured in fluid ounces for smaller applications.
Dry Flowable
The second common type is Dry Flowable or Wettable Powder, frequently labeled as “90DF,” meaning the product is 90% active ingredient by weight. The product label is the only legal and accurate source for the precise concentration percentage of the specific container you possess.
Determining the Required Application Rate
Mixing per gallon is only possible after establishing the correct application rate per area. The specific rate is determined by factors like the target weed species, the stage of weed growth, and the crop or turf being treated. Soil characteristics, such as organic matter content and texture, also play a role because they affect how the herbicide is held in the soil.
The product label defines the maximum legal rate, typically given as pounds of active ingredient per acre (lbs ai/A) or fluid ounces of product per 1,000 square feet (fl oz/1000 sq ft). Federal regulations set strict limits on the maximum amount of active ingredient that can be applied per acre per calendar year. Exceeding the rates specified on the label is illegal and can lead to crop injury, environmental contamination, or inadequate weed control.
The Calculation: Mixing Atrazine Per Gallon
The amount of atrazine product to add to a gallon of water links the required product rate to the water volume delivered by your sprayer. The water volume acts as the carrier to ensure uniform coverage, but the amount of product is dictated solely by the area being treated. The first step involves calibrating the sprayer to determine how many gallons of water it takes to uniformly cover a known area, such as 1,000 square feet. This calibration step is foundational for small-scale applications because it establishes the relationship between water volume and surface area for your specific equipment.
Once the sprayer’s delivery rate is known, you must calculate the total amount of product needed for the area covered by your tank volume. A simplified conversion equation helps derive the final product amount per gallon of water: (Product Rate per Area) / (Gallons used to cover that Area) = (Product per Gallon of water). This ensures that the correct amount of active ingredient is delivered to the target square footage, regardless of the total water volume sprayed.
For a concrete example, assume a label calls for 2.0 pounds of active ingredient per acre (lbs ai/A), and your sprayer calibration shows that one gallon of water covers exactly 1,000 square feet. Since one acre is 43,560 square feet, the 2.0 lbs ai must be spread over 43.56 gallons of water to maintain the correct concentration. If using an Atrazine 4L product (four pounds of active ingredient per gallon), you would need 0.5 gallons of product to get 2.0 lbs ai. Dividing 0.5 gallons (64 fluid ounces) by 43.56 gallons of water results in a final mix of approximately 1.47 fluid ounces of the 4L product per gallon of water.
If using an Atrazine 90DF dry flowable product at the same rate, the calculation changes to weight. Since 90DF is 90% active ingredient, you would need 2.22 pounds of the 90DF product to deliver 2.0 lbs of active ingredient. Converting this to grams (1,007 grams) and dividing by the 43.56 gallons of water needed to cover the acre yields approximately 23.1 grams of 90DF product per gallon of water. These examples illustrate that the final amount of product measured into the water is a direct result of the product’s concentration and the target area dose.
Mandatory Safety and Equipment Precautions
Working with concentrated herbicides requires adherence to safety protocols to protect the applicator and the environment. Personal Protective Equipment (PPE) is required when handling atrazine concentrates, and typically includes wearing a long-sleeved shirt, long pants, chemical-resistant gloves, and eye protection. For concentrated dry flowable products, a respirator may also be necessary to prevent inhalation of fine particles during measuring and mixing.
Mixing should always occur in a well-ventilated area. The herbicide product should be added slowly to a partially filled tank of water, not the reverse, to minimize splashing and foaming. Dedicated measuring devices must be used only for pesticides to prevent cross-contamination. Following application, excess mixture should be applied to a labeled site at the legal rate, and never poured down a drain or onto bare ground. Deviating from the specified application rates, methods, or safety instructions constitutes a violation of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).