Wyoming Weed & Pest Designated List

Hoary Alyssum (Berteroa incana)

BerteroaHoary alyssum, a member of the mustard family, is a tap-rooted perennial, biennial, or annual, that spreads through seeds. It produces small, white flower clusters that have four petals, which are deeply lobed. The plant has a rosette stage with leaves that get progressively bigger and have light colored mid ribs. The stems and leaves of hoary alyssum are very narrow and are covered with short, white hairs. The seeds are fairly large, oval-shaped, and laterally flattened. It is considered toxic to horses causing a number of different symptoms. Please contact SCWP to learn how to help manage this invasive weed, what works best in your area and how to use it safely.

Cheatgrass (Bromus tectorum)

a.k.a Downey BromeCheatgrass
ID Facts: Annual grass. Plants are usually 12 to 18 inches tall
Inflorescence is slender 3/8 to 3/4 inch long, drooping; usually turns purple at maturity.Leaves are flat and covered in soft hairs.
Reproduces from seed. Likes to establish in disturbance areas.The key to eradicating cheatgrass is diligence—once you begin the process you must be persistent and continue follow up treatments for up to four or five years (or however long it might take) because cheatgrass seed may survive in soils this long.
*After maturity cheatgrass becomes a nuisance and a fire hazard.

cheatgrass - fully cured seeds

Austrian Fieldcress ( Rorippa austriaca (Crantz) Bess.)




Austrian fieldcress is a more recent invasive plant in Sublette County. Early detection of this plant by weed & pest officials is vital to preventing this invasive plant from taking hold.

Austrian fieldcress is identifiable by erect smooth stems that branch at the top. Leaves are narrow and oblong, arranged alternately along the

Austrian fieldcress

Austrian fieldcress

stem.  The leaves are distinct because of their toothed edges and bases that clasp the stem. The yellow flowers grow in loose clusters at the tips of branches. They have four small petals and six stamens.  The small, rough, brown to black seeds generally do not develop at our elevation with a short growng season.

This plant mainly reproduces vegetatively by creeping roots, and rarely by seed.

austrian fieldcress detail

Field Scabious ( Knautia arvensis (L.) Coult)


Field Scabious is a perennial  that grows in grassland on well-drained, especially basic soils. It is a member of the teasel family with a deeply-penetrating, somewhat woody taproot. Lower leaves are pinate, lance-shaped, with toothed margins, and form a basal rosette. Upper leaves are stalkless and pinnate with 3-6 segments at each side with a terminal lobe.

The flower heads are usually pale lilac or light blue and comprise about fifty densely packed purplish-blue florets. The flowers resemble a round pin cushion.

Western Water Hemlock (Cicuta douglasii (DC.) J.M. Coult. & Ros)


Western water hemlock is a highly toxic member of the Parsnip Family. Western water-hemlock is found in sloughs, wet meadows, along streams and other wet areas. This plant is poisonous to all types of livestock and to humans.

Leaves are alternate, compound, twice or thrice divided, with petioles that partially sheath the stem. Stems are erect and solitary. Stems are hollow and smooth, branching, swollen at the base, and purple-striped or mottled. Flowers are white and compounded, flat-topped, umbrella-like clusters at ends of stems and branches.

Scentless Chamomile ( Matricaria perforata Merat)

Scentless chamomile, also known as mayweed, scentless mayweed or daisy, has white daisy-like flowers and its finely divided fern-like leaves. The flowers grow individually at the ends of smooth, erect branches.

Plants range can grow up to 3 feet in height and tend to be bushy when not subjected to competition. The seeds are dark brown, 2 mm long, rectangular and have prominent wing-like ribs that are paler than the kernel. The root system tends to be large and fibrous but does not run or creep.

Scentless chamomile can be mistaken for ox-eye daisy. These plants can be differentiated by their leaves, as scentless chamomile has finely divided leaves while those of ox-eye daisy are entire and notched but not divided. Scentless chamomile has several to many flowers on each flowering stem while ox-eye daisy has a solitary flower on each flowering stem.


Black Henbane (Hyoscyamus niger L.)


Black henbane is an annual or biennial plant that grows up to 3 feet tall. The stems and leaves are covered with greasy hairs. Shallow lobed leaves are up to 8 inches long and 6 inches wide.

Flowers are showy, 5 lobed, up to 2 inches across, black and white in color with distinct veins.

The calyx forms a 1-inch, urn-shaped “fruit” that has a thickened lid that pops off at maturity and spills the black seeds. Black henbane has very distinct skeletons with the urn shaped fruit filled with seeds still attached.bh2

black henbane flower

Russian olive (Elaeagnus angustifolia L.)


Russian olive is a small thorny shrub or small tree. Stems, buds, and leaves have a dense covering of silvery to rusty scales. Leaves are egg or lance-shaped, smooth margined, and alternate along the stem. At three years of age, plants begin to flower and fruit. Yellow flowers appear in summer and are later replaced by clusters of abundant silvery fruits.Russian Olive

Common Tansy (Tanacetum vulgare)


Common Tansy is a perennial herbaceous plant, 3-5′ tall in shaded areas. Each stem branches extensively toward the top into short stems forming a flat-topped cluster of numerous button-like flower heads. Pinnate leaves grow us the stems, getting smaller towards the top. Common tansy has been used for medicinal purposes.tansy

Common St. Johnswort (Hypericum perforatum)


Common St. Johnswort is a perennial plant about 1–2½’ tall with frequent branches. Stems are round, hairless, and light green; the larger stems have a pair of small longitudinal ridges. The opposite leaves are oblong, hairless, and sessile. Flowers are about ¾” across, consisting of 5 yellow petals, 5 green sepals, 3 styles, and numerous stamens (more than 20). The root system is rhizomatous, and produces numerous basal offshoots around the base of the plant.St. johnswort, noxious weeds