Leafy Spurge
Description and Variation: Description and Variation: Leafy spurge is a perennial plant with erect stems 1.5 to three feet tall. These stems originate from a crown just below the soil surface. The plants begin growing in early spring, before their competitors, and tend to appear in patches. Alternate leaves, three inches in length and no more than 1/4 inch wide, crowd along the stem; they are yellow-green from mid-summer to fall, when they turn red with the first frost. Leaves, stems, and roots all exude a milky, irritating sap when broken. In late May or early June, showy yellow bracts appear toward the tips of the short terminal branches, followed in a week or two by inconspicuous small green flowers without petals. Seed production takes about a month and continues until cold weather. Seeds, borne three to a capsule, are about 1/10 inch in diameter, gray to brown in color and often flecked with yellow. The seeds can be shot 20 or more feet when the capsule ripens and explodes. Another unique characteristic of leafy spurge, which contributes to the plants ability to persist once it invades an area, are numerous stem buds which cover the thick very invasive roots. These stem buds can initiate growth when broken into small segments by tillage and are transported by birds, grazing animals, or in soil.
Economic Importance: Economic Importance: Leafy spurge reduces the livestock carrying capacity of pasture and rangeland by 20 to 50 percent, causing an estimated $35-45 million loss per year in United States beef and hay production in addition to the millions of dollars spent for control. In Europe, natural controls keep leafy spurge from becoming a problem.
Destroy by July 15 and retreat again between September 20 and a killing frost.
Description and Variation Description and Variation: Hoary cress is a perennial plant with a spreading root system from which many aerial shoots are produced. The stem is 30-60 cm, erect to occasionally nearly procumbent. The basal leaves are irregularly dentate to entire with scattered to dense pubescence. The middle and upper leaves are sparsely pubescent to glabrous, obovate, elliptic-oblong or lanceolate, irregularly toothed to nearly entire. The flowers are white and the seed pods are heart shaped.
Economic Importance Economic Importance: Detrimental - Cardaria draba is the most weedy of all three Cardaria species occurring in the United States. It has the potential to reduce the value of high-price wheat lands. Beneficial - The flowers of hoary cress serve as pollen and nectar sources for many insects
Destroy before plant blooms.
Destroy by July 1
Description and Variation: Canada thistle is a perennial herb with a deep-seated complex system of roots spreading horizontally which give rise to aerial shoots. The one to four foot tall stems are slender, green, and freely branched. The leaves are alternate, sessile, and deeply lobed. The leaf margins have stiff yellowish spines. The heads are many and relatively small. The plants are dioecious (all flowers on a plant are either male or female). The flowers are purple. The fruits are about 1/8 inch long, somewhat flattened, and brownish with an apical circle of long hairs, these eventually falling. Four varieties of C. arvense have been recognized based on variation in leaf characters, texture, vestiture, segmentation, and spinyness.
Economic Importance: Detrimental: C. arvense is found in virtually all crops, and is also found in pastures and rangelands where it reduces forage. The weed is an effective competitor for light, moisture, and nutrients and is thus able to reduce crop yields. C. arvense also serves as an alternate host for insects and pathogenic microorganisms that attack various crops.
Destroy by July 15
Description and Variation Description and Variation: A bushy, branched perennial, Russian knapweed grows one to three feet tall and forms clones or colonies from its vigorous, spreading root system. The erect, hairy stems branch from above the middle or not at all. While young plants may have whitish and woolly stems, older plants will turn dark brown to black. The basal leaves are deeply notched and gray-green in color, while the upper leaves are smaller and linear with broken edges. The stem leaves are intermediate in size with toothed edges. The pink to purple flowers grow in solitary heads at the tips of leafy branches. The bracts under the flower heads are greenish to straw colored, with a broad, papery tip. Russian knapweed flowers from June to September, producing ivory-white seeds with a feather-like plume.
Economic Importance Economic Importance: Russian knapweed is an aggressive and invasive noxious weed of pastures, non-crop areas, grain fields, and other cultivated fields. Livestock may avoid this species; in addition, the plant is poisonous to horses, causing chewing disease (nigropallidal encephalomalacia).
Destroy by July 15
Description and Variation Description and Variation: Diffuse knapweed is an 8 to 40 inch tall, biennial or short-lived perennial species, with a long tap root. The single, upright stem produces several spreading branches. The basal leaves are short-stalked and divided into lobes on both sides of the center vein. The stem leaves are stalkless, becoming smaller and less divided near the top of the stem. The flowers, which are generally white (sometimes pink or lavender), occur in urn-shaped heads that grow in clusters at the ends of the branches. The bracts of the flower heads are leathery, with obvious veins. The lower and middle bracts are yellowish-green with a buff or brown margin; they are edged with a fringe of spines plus a longer, spreading spine at the tip.
Economic Importance Economic Importance: Diffuse knapweed is a very aggressive species that can infest large areas quickly. The species has little value as forage for cattle and limited seasonal value for big game. Knapweed infestations increase production costs for ranchers, impair the quality of wildlife habitat, decrease plant diversity, increase soil erosion rates, decrease the visual quality and appeal of recreational lands, and pose wildfire hazards.
Destroy by July 15Description and Variation: Spotted knapweed is an eight to 48 inch tall perennial with a stout tap root. The plant is hairy and rough with a somewhat woolly appearance. The leaves, which are once or twice divided into lobes on each side of the center vein, are blue-gray in color. The overwintering rosettes bolt in early summer, producing 1-15 stems. The stem leaves, which have a few lobes or are linear, become smaller toward the top of the plant. The pink to purple flowers (rarely white) occur in egg-shaped to oblong heads, which are solitary at the ends of clustered branches. The bracts of the flower heads have obvious veins, with a black spot on the tip. The lower and middle bracts are egg-shaped, and green to brown below the tip. The tip and upper bract margin have a soft spine-like fringe, with the center spine being shorter than the others. White-flowered plants usually lack the dark spot on the bract tip. The plant flowers from June to October, producing black to brown, oval seeds with pale lengthwise lines, and a ring of slender, chaffy bristles.
Economic Importance: Spotted knapweed is a very aggressive species that can infest large areas quickly. The species has limited value as forage for cattle and seasonal value for sheep or big game. Knapweed infestations increase production costs for ranchers, impair the quality of wildlife habitat, decrease plant diversity, increase soil erosion rates on valuable watershed areas, decrease the visual quality and appeal of recreational lands, and pose wildfire hazards.
Destroy by July 15
Destroy by July 15
Description and Variation Description and Variation: Rush skeletonweed belongs to the chicory tribe of the sunflower family. This herbaceous perennial ranges from one to four feet tall, with a taproot reaching down seven feet, or more. The seedlings have a long thin taproot. Rush skeletonweed overwinters as a rosette of hairless, basal leaves that are two to five inches long and ½ to 2 inches wide and broader at the tip. The lateral lobes point back toward the base - very similar to a dandelion. The mature plant consists of a dark green, nearly leafless flowering stem, with many aerial branches. The basal rosette is absent at this stage. The stem and aerial branches support a few leaves, which are narrow and linear, and mostly entire. A distinguishing characteristic of rush skeletonweed is the presence of coarse, downward pointing brown hairs near the base of the stem. The stems and roots of rush skeletonweed exude a white latex sap when cut. The flower heads, about ½ inch in diameter, grow along the stem in the leaf axil or at the branch tips, and they are found individually or in clusters of twi to five. Each flower head has 7-15 (usually 11) ray flowers, with yellow ligules resembling petals. These yellow ligules are strap shaped with small teeth across the blunt end. Mature, vigorous plants can produce 1,500 flower heads, with the capability of producing 20,000 seeds. The immature seeds are greenish-white, and they gradually darken to a yellow-brown or olive-green in the 13-15 days it takes to mature. The seed color can be used as an indication of maturity, with light colored seeds showing low germination rates (Old 1981). Each seed has a pappus, which is capable of carrying seeds along wind currents up to 20 miles (Cuthbertson 1967 and Schirman and Robocker 1967 as cited in McLellan 1991).
Economic Importance Economic Importance: Detrimental: Rush skeletonweed is a threat to irrigated lands of the Columbia Basin, to the sandy soils of dry land wheat areas (Old 1981), and it is a threat to rangelands. Rangeland infestations impact the cattle industry when rush skeletonweed displaces native or beneficial forage species grazed by livestock and wildlife. Forage production is lowered when rush skeletonweed successfully outcompetes beneficial species for limited resources, particularly nitrogen. Often, the cost of herbicide control is not economical due to low productivity of the land (Sheley)
. Destroy by July 15
