Wyoming Weed & Pest Designated List

Dalmatian toadflax (Linaria dalmatica (L.) Mill.)


Dalmatian Toadflax, a member of the snapdragon family, was introduced as an ornamental plant, and is a noxious weed in Wyoming. Flowers are bright yellow with two ‘lips’ and spurs at the bottom. Even from early stages, Dalmatian Toadlfax can be distinguished from Yellow Toadflax by the broad heart-shaped leaves that clasp the woody stems.

Dalmatian Toadflax rosettes exhibit the wide, heart-shaped leaves that distinguish it from Yellow Toadflax.

Yellow toadflax (Linaria vulgaris L.)


Yellow Toadflax was introduced as an ornamental plant, and is a noxious weed in Wyoming.  It is known as ‘snapdragon’ or ‘butter and eggs’ because of it’s distinct bright white and yellow flowers with two ‘lips’ and long spurs. It can be differentiated from Dalmatian Toadflax by the numerous long, narrow, thin leaves that appear even in the rosette stage.IMG_1311

Russian knapweed (Centaurea repens L.)


Russian Knapweed is a perennial that grows 18 to 36 inches tall with many branches.  Shoots and leaves are a sage color, and covered in dense gray hairs. Single urn-shaped flowers appear at the tips, and flower out to be a purple, pink, or white color. It is toxic to horses if eaten. Chemical mechanical control must be combined to effectively control Russian Knapweed.

Skeletonleaf bursage (Franseria discolor Nutt.)


Skeletonleaf Bursage is a perennial, that can grow up to 1 ft tall with extensive creeping rootstocks. The upper leaf surface is greenish-gray and coarsely toothed while the lower surface is white with short, dense hairs. Flowers are inconspicuous and yellow. This is a native plant that is considered noxious.skeletonleaf bursage

Ox-eye daisy (Chrysanthemum leucanthemum L.)


Ox-eye daisy, a member of the aster family, is a perennial that was introduced to the United States as an ornamental plant. It grows 1-3 feet tall with flowers that have white ray florets surrounding numerous tiny yellow disk florets. It can be distinguished by oblong, alternate leaves with distinct rounded teeth along the edges, and a clump of rosette leaves at the base. Leaves become progressively smaller up the stem.

Ox-eye daisy is sometimes mistaken for a wild flower, but it can be harmful to the native ecosystem. It is illegal to plant ox-eye daisy in Wyoming, but some recommended substitutes in gardens are Shasta daisy or blanket flower.

Hoary cress (whitetop) (Cardaria draba & Cardaria pubescens (L.) Desv.)


Hoary cress, commonly known as little whitetop, has arrowhead shaped leaves, and white 4-petal flowers.

A hoary cress seedling is a cluster of long, slightly serrated leaves.


Flowers will appear as small blue or purple balls before flowering out into many clustered white, 4 petaled flowers.


Hoary cress can be identified by the distinct arrowhead shaped leaves clasping the stem.



Quackgrass (Agropyron repens (L.) Beauv.

Quackgrass leaf sheaths are rounded and may have short hairs but hairs typically can be found only near the base of the plant. Leaves are rolled in the bud and are approximately 1 1/2 to 12 inches long.

Leaves may or may not have hairs on the upper surfaces, but lower leaf surfaces are without hairs.

Seedheads are a long, narrow spike consisting of many individual spikelets arranged in 2 rows along the stem.

Perennial sowthistle (Sonchus arvensis L.)


Perennial sowthistle stems are erect, stout, smooth, and unbranched except at the top. The clasping leaves are alternate and light green, and slightly toothed. Perennial sowthistle can grow anywhere from 4 to 6 feet tall, reproducing by seeds and horizontal roots. The flowers are large and yellow, resembling a dandelion.
sow thistle, noxious weedsIMG_1293

Canada thistle (Cirsium arvense L.)


Canada thistle has waxy, kelly green, serrated leaves and stems that branch out into many flower heads. Flowers are purple in the early season, and become white when ready to go to seed

Canada thistle is a perennial that spreads from both seeds and root systems, which makes control particularly difficult. Infestations usually begin in disturbed soil, and a combination of control methods are needed to eliminate it.