May 16, 2008

Common mullein (Verbascim thapsus) is a weed species that's increasing in northeastern Nebraska's rangeland, woodland, and pastures. A biennial plant, it reproduces only by seeds, but is a prolific seed producer. The taproot of this species can access soil moisture from a deeper profile faster than fibrous roots of pasture grasses, giving common mullein the competitive advantage over grass, especially during dry years.

Figure 1. Common mullein (Verbascim thapsus) in a Nebraska pasture.

Common mullein usually starts growing sparsely as individual plants and then spreads. A cluster of leaves, commonly known as a rosette, with a thick hair cover is a distinct identifying feature of this species. The stem is woolly, erect, 2-6 feet tall and doesn't have branches. Leaves are opposite, elliptic to ovate. Like many other plant species, the overall growth and development depends on the amount and timing of rainfall. In Nebraska common mullein can flower in June and July with yellowish flowers. It has a low palatability and no value to livestock.

Control Options

Ranchers need to control this species because heavy stands can reduce grass production as much as 50%, especially in dry years. The best strategy is to control common mullein when the population is limited. Density of this species can easily expand from a few plants to hundreds of plants per acre over just a couple years due to prolific seed production.

Mechanical. Sparse populations can be controlled by mechanical removal using a spade or shovel in late April or early May. Individual plants can be dug out or cut just at the soil surfaces as long as whole rosette is removed. Single mowing of new 1- to 2-foot tall plants can reduce population and seed production for the season, especially in dry years.

Chemical. Herbicides also can be effective tools in providing season long control; however, the thick wooly coat of hairs on the leaves can reduce herbicide uptake and control. Apply herbicide when the rosette has 6-12 leaves and before the stem starts to grow, usually in May.

Effective herbicides and their rate per acre include: Grazon P+D (3-4 pts/ac), Cimarron (0.75-1 oz/ac), and a three-way-mix of Cimarron (0.5 oz ), Glean (0.5 oz) and RangeStar (32 oz). Make sure to use enough additives such are crop oil concentrate at 1-2 qt/ac to help herbicide penetrate the thick wooly coat.

Stevan Knezevic
Extension Weeds Specialist
Haskell Ag Lab, Concord, Northeast REC