July 6, 2019
July 8, 2019

Dogfennel is a perennial weed that resembles many other types of weeds, including maywood chamomile, pineapple weed, and horseweed. It may be referred to as cypressweed or tall fennel and its scientific name is Eupatorium capillifolium. Whatever the name, it is often seen in pastures and areas of thin turf and can be especially troublesome to eradicate. Fuzzy and noxious, dogfennel is a perennial weed that can be extremely difficult to control. The best method of defense in lawns and landscapes is prevention in a manicured, well-cultivated space. 

Although dogfennel can be mistaken for other types of weeds, there is a distinct difference between dogfennel, pineapple weed, and horseweed. When crushed, dogfennel has an unpleasant odor that is described as both sour and musty. This weed can grow to a height of over 6 feet. Its stems become woody at the base, and its root system is fibrous and matting making thin landscaping and overgrazed pastures the prime location for dogfennel to grow. The leaves of the plant are extremely thin and can be thready and fern-like, giving it an almost feathery appearance. While it does produce flowers, they are extremely small and range in color from white to a pale green. Stems are reddish in color, woody at the base, and hairy. 

This short-lived perennial weed is native to the United States. It is predominant in the southeastern United States growing from New Jersey, down the eastern seaboard, then across to Texas. It can usually be found in places with sparse vegetation and adds to the decline of forage yield and quality. 

Dogfennel does not tend to grow well in thick, established turf and landscape. It reproduces mostly by overwintering rosettes, but it also produces seeds that contribute to the spread of this invasive weed. Seeds will generally begin to sprout and grow when temperatures reach 65 degrees. They go dormant from January until March but will resume bolting from April through June. Seed dispersal occurs just before dormancy in late November and December. When found in pastures, livestock tend to avoid grazing on the plants as they aren’t very palatable and emit a foul odor. However, when there is low-quality grass and feed available, as tends to happen in overgrazed pastures where dogfennel thrives, livestock will consume the weeds. It is considered toxic to cattle as the leaves contain low levels of a toxin called tremitol, which causes dehydration when ingested by livestock.

The best course of weed control for dogfennel is cultivating and maintaining a thick and established landscape. It is possible to mow the plants when they are still short to stress them before they reproduce. If there are only a few of these weeds in your landscape, digging them out carefully and removing their matted roots will help eliminate the growth of dogfennel. However, because it can reproduce via rootstock, it is important to carefully remove all parts of the plant and dispose of it carefully to avoid any of the plant material from taking root again and reestablishing itself. Additionally, there are several types of herbicides that have been shown to be effective in eliminating dogfennel as long as it is less than 20 inches tall. Herbicides work best on actively growing weeds and in the seeding and flower stage of growth.