What Is Treflan Herbicide?

Treflan is the brand name of a line of herbicides produced by Dow AgroSciences, LLC. Many Treflan formulas are meant for agricultural use, but Treflan EC Weed and Grass Preventer is available to homeowners. The main ingredient in Treflan, a deep, clear orange liquid packaged in plastic jugs, is trifluralin, a man-made chemical used to control annual weedy grasses and broadleaf weeds in the garden. Always wear eye protection, long pants, socks and shoes, long-sleeved shirt and chemical-resistant gloves when applying Treflan -- or any chemical -- to yards.

worker sprays pesticide on potato plantation
credit: VvoeVale/iStock/Getty Images
Man spraying herbicide on garden.

Active Ingredient

Trifluralin is a selective, pre-emergence herbicide, which means it prevents certain weeds and weedy grasses from ever germinating or getting the chance to grow in the yard. According to the U.S. Environmental Protection Agency's website, Trifluralin has caused some abnormalities in test animals. This orange, crystalline chemical is highly toxic to aquatic wildlife and should never be used close to water sources or allowed to drift or run off into water sources. Treflan has a generally low toxicity to humans, but can sometimes trigger an allergic effect if it directly contacts the skin. It can be inhaled or absorbed on direct contact with the skin, but the long-term effects of exposure are unknown.

Application Rates

The amount of Treflan depends on the type of soil in your garden. The product label contains instructions for using Treflan on light or coarse soils such as sand, sandy loam and loamy sand; medium soils, defined as silt or loam; and fine or heavy soils, which are clay, clay loams, silty clay and silty clay loam. Add 2 1/4 teaspoons of Treflan to 1 gallon of water for coarse soil, 3 1/3 teaspoons per gallon for medium soils and 4 1/2 teaspoons per gallon of water for fine soils. Fill the sprayer tank half full of water, add Treflan, then finish filling the reservoir. Stir or agitate the mixture thoroughly to blend.

When to Use Treflan

Treflan can be applied in early spring, directly before planting or as much as three weeks before. Treflan can also be applied to the soil in the fall, before the first frost, to help control next year's weeds, with a second application in the spring once the soil is workable.

Apply Treflan

Treflan should be applied directly to the soil and worked into the top 2 to 3 inches of soil. The product may be used before planting or after plants germinate. Spray the Treflan mixture to thoroughly coat the soil. Use 1 to 5 gallons of mixture to 1,000 square feet of soil -- whatever it takes to provide complete coverage. Use a shovel, hand rake or any other garden tool that will turn and mix the soil with Treflan and simultaneously break up dirt clods. Do not apply in areas of the garden where you plan to direct-sow any type of cucurbit (Cucurbitaceae) or sweet corn (Zea mays var. saccharata). Do not allow children or pets to enter treated areas until the product dries completely.


Audrey Lynn

Audrey Lynn has been a journalist and writer since 1974. She edited a weekly home-and-garden tabloid for her hometown newspaper and has regularly contributed to weekly and daily newspapers, as well as "Law and Order" magazine. A Hambidge Fellow, Lynn studied English at Columbus State University.