Dogfennel (Eupatorium capillifolium), which some people refer to as summer cedar, is a perennial weed that can be difficult to control. When mowed down or cut it grows back from a woody base. Additionally, it produces seeds with hairs that can travel long distances by the wind. If that’s not enough, it can grow up to 8 feet tall and is very narrow making it hard to spray with herbicides. So how do we control this weed?

Biology

It’s important to know the characteristics and growth habit of dogfennel to better be able to control it. Dogfennel is a perennial, so it lives for more than two years. However, it still flowers and produces seed that turn into new plants. These seeds are primarily transported by the wind and readily germinate when soil temperatures reach 65°F. Dogfennel also sprouts from underground rootstocks that develop from the main taproot allowing a single plant to colonize a small area in just a few years.

Dogfennel colony resulting from lateral spread from rootstocks. Photo Credit: Jason Ferrel, University of Florida/IFAS

Control

Dogfennel’s ability to regrow from underground rootstocks makes it pretty resistant to mowing. Like most weeds, smaller plants are easier to control than larger ones. For pastures, herbicide recommendations are based on dogfennel height. These recommendations can be considered for home landscapes as well. A product containing 2,4-D amine or 2,4-D amine and dicamba together such as Ortho Weed B-gon Weed Killer for St. Augusitinegrass or BioAdvanced Southern Weed Killer For Lawns can be used on most warm-season turfgrass species. However, please read the label carefully because rates vary based on turfgrass species. These products are recommended for dogfennel less than 36 inches tall. Products containing triclopyr or fluroxypyr or a mixture of the two can control dogfennel taller than 36 inches. But, please follow the label because spot treatment may be necessary for some turgrass species. Spot treatment can also be used with a product containing glyphosate.

Another thing that makes dogfennel difficult to control is its ability to survive in poor soils and drought conditions. It is perfectly happy living in spots where other plants may suffer. So keep that in mind once you have removed dogfennel from areas of your yard. You may want to test the soil in these areas and amend the soil to support desired plant material.

Washington County

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