Dogfennel (Eupatorium capillifolium) is native to North American and can be a tall annual or short-lived perennial. Dogfennel has densely hairy stems that come from a woody crown. The leaves are deeply dissected that give off a hairy or feathery appearance. If the leaves are crushed, they give off a distinct, pungent smell. The flowers on dogfennel are greenish-white in color and appear in midsummer until the first frost. Dogfennel can grow 6 feet or higher. In later months, the lower leaves can fall off, which gives the plant a more shrub-like appearance that shows off the red-brown stems.
Dogfennel is very common throughout South Carolina and is a weed in pastures, abandoned fields, waste areas, and roadsides. Dogfennel likes full sun, but can be found in areas of partial shade. It can establish small colonies of plants in time and is capable of sprouting multiple plants from the main rootstock. Dogfennel produces a large quantity of seeds each year, which will germinate in the following years.
Regular mowing can keep dogfennel controlled in home lawns. Thick stands of turfgrass with proper fertility and irrigation reduces the competitiveness of this plant. Young plants have stems that are easily broken, but do become more difficult and woodier as the plant matures. Removal of individual plants can be difficult do to its fibrous root system. Hand-removal of seedlings is effective before the root system develops extensively. Mulching landscape beds can inhibit the germination of dogfennel. A mulch layer that is 2-3-inch-deep can aid in suppressing weed growth.
Dogfennel is susceptible to a wide variety of herbicides, but should be sprayed prior to reaching 20 inches in height. Application of herbicides prior to reaching this height provide better control. Applications should not be made during prolonged dry weather, because drought causes the plants to “harden off” in an effort to conserve water.
Application of herbicides can be made at any time, but for best control, applications should be made at the seedling or immature stage to prevent seed development. Several herbicides containing 2,4-D, mecoprop (MCPP), and dicamba, known as a 3-way herbicide, are available to homeowners for post-emergent control. A 3-way herbicide can be used to spot treat dogfennel in lawns with tall fescue, bermudagrass, and zoysiagrass. Areas with centipedegrass or St. Augustinegrass may need reduced rates, which is stated on the product label.
Herbicides containing iodosulfuron, dicamba, and thiencarbazone are also effective on bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass. Glyphosate will have less soil activity to injury nearby plants in a landscape bed. Spring applications of isoxaben, a pre-emergent, can also reduce dogfennel in lawns and landscape beds.
Injury to grasses can occur if post-emergent products are applied during the spring green-up (the time between dormancy and active growth), or if applied during excessively hot (>85F) and dry times during the summer. Take precautions when spraying close to desirable landscape plants to prevent off-target applications and damage.
For more information on dogfennel and examples of postemergent herbicides, please visit the Home and Garden Information Center website at hgic.clemson.edu. Tune in on Tuesday nights to watch “Making it Grow” at 7 p.m. on SCETV or mig.org. E-mail Outen at callenb@clemson.edu.
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