Mugwort - A Potential Weed Pest of Plant Beds

"It looks like chrysanthemum, even has a fragrant aroma, but it doesn’t have the nice showy flowers."

"It also looks somewhat like common ragweed, but the leaves are not as deeply dissected."

The weed in question turns out to be mugwort (Artemisia vulgaris). Well, it’s a close cousin of both chrysanthemum and ragweed since it is a member of the same botanical family - asteraceae, or, simply, the asters.

In recent years, several samples of this plant have been submitted to my office for identification. When the samples (live tissue or digital photograph) arrived, I quickly flashed back to my childhood on the east coast. I could vividly remember the long days of useless hand pulling this pest from my parent’s vegetable garden.

Mugwort, like many of our weed pests, is an introduced species from Europe. Once brought into the eastern United States, it spread westward, largely via container ornamentals, a prime habitat. In Missouri, the first record of its presence was in St. Louis County.

The plant is a clump-forming perennial that regenerates from its underground rhizome system. It rarely reproduces by seeds in our climate. Fragments of viable rhizomes can easily be transported by infested nursery stock, topsoil, or compost. The young leaves are opposite on the main stem, with white, woolly hairs on the undersides. Leaves are on petioles; the older leaves are deeply lobed, pointed, and occur alternately along the stem. Left unmowed, the stems become woody with age and are often red, brown, or purple in color. Flowers are inconspicuous as they are greenish-yellow, occur in spikes, and aren’t produced until July.

Unfortunately, there are no practical selective herbicidal control measures available. Once established, mugwort will probably be here to stay, as it is well adapted to mowing and cultivation. It tolerates mowing at heights lower than is recommended for maintaining cool-season lawns. Prevention is the key to avoiding this problem; thoroughly inspect all container-grown stock before planting into your garden. Visible presence of this weed should be an indicator of sure signs of future problems.

Fred Fishel, Extension Pest Management/Pesticide Training Coordinator, UMC (573)884-6361