Extension by Brian MealorWritten by Brian Mealor
New alien sightings have increased in Wyoming over the past several years. Before you quickly move to, “What in the world are those people at the University teaching our kids?!!” I must clarify that these are “alien” plants – those not native to our area and considered invasive weeds in neighboring states.
Several new invasive plant species have been found in Wyoming over the past two summers. Were they found near you? Are they something you might have seen before and not realized it is a potentially problematic weed? I will give a brief description of these alien sightings in Wyoming so you can keep an eye out for these aliens in your area.
Moth mullein (Verbascum blattaria) was found and reported by Natrona County Weed and Pest late this summer along Interstate 25 north of Casper. Much like its close and more abundant relative common mullein, moth mullein is frequently associated with areas where the soil has been disturbed. The population found and reported was growing in an area that had been disturbed by recent construction activities.
Moth mullein is a biennial, meaning it lives for two years. The plant has very attractive yellow or white flowers that some people think resemble a moth. It spends its first year of growth as a basal rosette, which is a relatively round cluster of leaves that grow near the soil surface without sending up a vertical flowering stem. It produces flowering stems and seeds during the second year of growth.
Although it is facilitated by disturbance, moth mullein has been documented moving into perennial forage crops, pastures and rangelands in other parts of the country, thereby reducing forage quality. It has been intentionally planted for ornamental purposes in some states, but its ability to invade natural areas makes it undesirable. An additional characteristic that makes it very difficult to control once a population becomes established is that the seeds it produces may stay alive in the soil for 100+ years. It is listed as a Class B noxious weed in Colorado.
Dame’s rocket (Hesperis matronalis) is not necessarily a new plant in Wyoming. This showy white to purple-flowered biennial mustard has been planted as an ornamental plant for quite some time.
However, in recent years it has been showing up in increasing numbers in areas where it has not been planted.
The plant has lance-shaped leaves with small teeth along the edges, but the large clusters of flowers are the most conspicuous and often-noticed characteristic. Many people have made the mistaken assumption that dame’s rocket is a native wildflower. It is often sold as such in “native wildflower” seed packets, but it was introduced from Europe many years ago. Once a population becomes established this plant can form dense stands which may exclude other desirable vegetation. Like many of our problematic mustards, control is difficult once patches become large. Dame’s rocket is also a Class B noxious weed in Colorado.
Several times since recently has another very problematic alien species made appearances in western Wyoming. Rush skeletonweed (Chondrilla juncea) is a perennial weed with a similar growth pattern to some weeds with which we are already familiar – Russian knapweed, Canada thistle and other creeping perennial species. It was found in Sublette County in 2006, Lincoln County in 2010 and Teton County in 2011. Other instances in Wyoming have been reported, but not documented formally.
Unlike the previous two plants discussed here, Rush skeletonweed is not grown as an ornamental plant. It was reportedly introduced as a forage contaminant in the early 1900s, and currently is estimated to populate millions of acres in the northwestern U.S. Its forage value is very low and once it becomes established it can form very dense stands which exclude other native vegetation. Early in spring it forms basal rosettes that look similar to dandelion, but as it develops it forms upright stems with reddish hairs angling downward at the base of the stem. The yellow flowers are quite small and the petals appear notched on the ends. Rush skeletonweed also produces a white milky sap that will ooze from stems and leaves when damaged.
Of these three aliens, rush skeletonweed likely poses the greatest potential for widespread ecological and economic impact in the state of Wyoming.
To be fair, alien weed species may not catch your attention as much as a glowing orb passing through the night sky. They probably will not be discussed by either presidential candidate as part of their platforms. However, invasive “alien” weeds impose significant harm to our natural resources in Wyoming.
The diligent work of Wyoming Weed and Pest, other agencies and you, as a citizen, in locating and managing newly emerging weed threats to our state will pay large dividends into the future. For more information about any of these plants, visit invasive.org, contact your local UW extension office or your county Weed and Pest District.