Species specifics: Dogfennel

Fast facts

Aggressive perennial native weed common in the Southeast.
Toxic to cattle when ingested, leading to dehydration.
Easily spreads by windblown seeds or rootstocks.

What to look for

Dogfennel (Eupatorium capillifolium) is a common native perennial weed that is toxic to livestock and can cause nightmares for cattle producers.

Easily reaching 6 feet tall in favorable conditions, dogfennel is a tall plant with finely dissected leaves that have a strong odor when crushed. At the bottom of the plant, the leaves alternate in opposite directions and are ¾ to 4” long. Tall stems are erect and branched in the upper part of the plant that are green to bronze in multiple branched panicles that produce greenish-white flower heads in the fall.

The weed spreads by both windblown seeds and rootstocks, which allow it to quickly take over a pasture. Once soil temperatures reach 65°F, overwintering rosettes will begin growing and newly dispersed seeds will begin sprouting. Dogfennel grows well in most soil types and moisture levels, which makes bare dirt or recently disturbed ground ideal environments for windblown dogfennel seeds to become established.

Typically, cattle will avoid dogfennel for more favorable forages, but if pastures have been overgrazed or the weed has reached infestations levels where little to no other favorable forages are available, cattle will eat it. Dogfennel contains trace levels of the toxin tremetol, which causes dehydration in cattle and can lead to a host of other problems in severe cases. Dogfennel is also toxic to horses.

Where it is found

Common throughout the United States, particularly in the Southeast, dogfennel is a regular foe in Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, Missouri, New Jersey, Oklahoma, Pennsylvania, Tennessee, eastern Texas and Virginia. Occasionally, dogfennel has also reached as far north as Connecticut and Massachusetts.

How to treat it

Because of its aggressive nature, dogfennel usually requires an aggressive management approach, especially when infestations increase beyond 25% ground cover.

Apply 24 to 34 fluid ounces GrazonNext® HL herbicide when plants are less than 12 inches tall or 20 to 32 fluid ounces of GrazonPD3™ herbicide per acre. Tank mix 16 to 20 fluid ounces of DuraCor® herbicide per acre + 8 to 12 fluid ounces of PastureGard® HL herbicide per acre for large dogfennel.

For non-residual weed control, apply 24 to 34 fluid ouncesPastureGard HL per acre to plants as tall as 48 inches.

Unsure which dogfennel treatment route is best for your pastures? Reach out to your local Range & Pasture Specialist.

GrazonPD3™ is a Restricted Use Pesticide. Always read and follow label directions. Under normal field conditions DuraCor® is non-volatile. DuraCor has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. Label precautions apply to forage treated with DuraCor to manure and urine from animals that have consumed treated forage. DuraCor is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. PastureGard® HL herbicide is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. GrazonPD3 is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. GrazonPD3 is not for sale, distribution or use in Nassau and Suffolk Counties in New York State. [EL4] GrazonNext® HL has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. Label precautions apply to forage treated with GrazonNext HL and to manure and urine from animals that have consumed treated forage. Consult the label for full details. GrazonNext HL is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. GrazonNext HL is not for sale, distribution, or use in New York State and San Luis Valley of Colorado. Always read and follow label directions.