South Dakota State Declared Weeds

Scott Guffey, Supervisor
Craig Smith, Crew Leader
Ruth Sisk, Secretary

Pennington County
Weed & Pest
3607 Cambell Street
Rapid City, SD 57701
Phone: (605)394-5320
Fax: (605)716-3793

Contact Weed & Pest

SOUTH DAKOTA FACTS:

According to a May, 2003, proclamation by South Dakota's Governor Mike Rounds, "noxious weeds infest over five million acres of South Dakota's pastures, cropland and wild areas...The direct economic impact of this infestation is over $80 million dollars....If not controlled, the total estimated cost of the weed infestation would be in excess of $180 million dollars."

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Canada Thistle Canada thistle infests about 1.7 million acres in South Dakota. These infestations can be found throughout Pennington County. Canada thistle numbers have gone up drastically in recent years, mainly due to increase rainfall in the spring and summer over the past several years. Canada thistle is a perennial, with a deep horizontal root system. Flowers are numerous vary in color form a light lavender to a rose purple or even white and are1/3 to 3/4 of inch wide. Flowers become a fuzzy down in mid to late summer when the plant is ready to set seed. Leaves are alternate, oblong, irregular and spiny. Stems are 1 to 4 ft tall, hollow and branching near the top. Canada thistle if left uncontrolled can quickly grow in to a large patch infesting acres and acres of land.

Hoary Cress Hoary Cress infests around 4,000 acres in South Dakota, there are no known infestation in Pennington County. Hoary cress is a perennial, roots are extensive both horizontally and vertically. Flowers are white small four petalled and borne in flat topped clusters. Leaves are alternate, oblong and grayish-green. Upper leaves clasp around the stem, lower leaves borne on petioles and both are wavy. Stems are stout, erect, branched toward the top and grow 2 ft tall. Plants emerge in very early spring, flower in April and can set seed from late May to July.

Leafy Spurge infests around 275,000 acres in South Dakota. In Pennington County its mainly found in the Black Hills, with the main infestation is around Hill City. Leafy spurge can also be found around the Deerfield area and around Rockerville. Pennington County Weed & Pest is trying to keep it from reaching the plains and the agriculture community, thus far there is no known infestation east of Rapid City. Leafy spurge is a perennial, reproducing by root and by a three celled seed head that can eject seed 15 feet when ripe. Flowers are a bright yellowish-green and fairly small, leaves are long and narrow. Stem are grow to 3 feet tall, thickly clustered and contain a poisonous milky white sap. The poisonous sap can irritate human skin, cause hair loss around the hooves of horses and cattle, irritate the mouth and digestive tract and may cause death.

Perennial Sowthistle Perennial Sowthistle infests close to 150,000 acres in South Dakota. A few scattered plants and patches are found in Pennington County. The number of acres infested was declining in SD but with recent increase rainfall perennial sowthistle is starting to make a comeback. Perennial sowthistle is a perennial, hence the name. The root system is deep and spreading. Flowers are bright orange-yellow, up to 1.5 inches across, in branched clusters. Leaves are alternate, vary shape with prickly edges and upper leaves are fewer and smaller than the base. Stems are erect 2 to 7 ft tall and has a milky juice through out the stem and root system. Perennial can spread fast especially in cultivated fields.

Purple Loosestrife This noxious weed infests about 1,200 acres in South Dakota. Small patches have been found on Rapid Creek, that are the only know infestations in Pennington County. Purple loosestrife is a perennial reproducing both by seed and root. Flowers are rose-purple in color, five to six-petalled and arranged in long spikes. Leaves are opposite, linear and with smooth edges. Stems are four or six sided, woody, branched and grows 3 to 8 ft tall. Purple loosestrife was introduced as an ornamental and up until recently was still being sold as one. It is an aggressive invader of aquatic sites.

Russian Knapweed This weed infests about 2,000 acres in South Dakota; however, there is no known infestations in Pennington County. Russian knapweed is a perennial, reproducing by deep, creeping roots and seeds. Flowers are white to lavender, small clusters on branched tips. Leaves are alternate and of a varied shapes, basal leaves are deeply lobed, upper leaves are narrow and short. Stem are erect, branched and grow 2 to 3 ft tall. Stems and leaves are covered with fine hairs, giving the plant a bluish-green appearance.

Salt Cedar Salt Cedar infests about 6 thousand acres in South Dakota. Most of Pennington County’s infections are along the Cheyenne River, with a few ornamental plantings scattered throughout the county. Salt Cedar is deciduous or evergreen shrub or small tree, 5 to 10 feet tall. Bark is reddish-brown, leaves are small and scale-like, and flowers are pink to white, 5-petalled. Large trees can transpire at least 200 gallons per plant each day and will often dry up ponds and streams.

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