Noxious Weeds of Nebraska Biology Identification Distribution Control
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University of Nebraska–Lincoln Extension EC176 (Revised March 2012) Noxious Weeds of Nebraska MuskMusk Fred Roeth, Emeritus Extension WeedsThistle Specialist Steve Melvin, former Extension Educator,Thistle Frontier County Irvin Schleufer, Agricultural Research Technician Mark Bernards, Extension Weeds Specialist Biology Identification Distribution Control Biology Musk lthough classified as a biennial plant ThistleThistle A(see Life Cycle, page 5), opportunistic might be a better descriptor because usk thistle (Carduus nutans L.) is an compete with native vegetation. musk thistle can behave as an annual or a introduced invasive broadleaf weed Musk thistles can invade all lands in M winter annual depending on the growing native to Europe, North Africa, and Nebraska. Typical cropland weed con- conditions. Musk thistle seedlings can Asia. In these areas it is a minor weed trol methods are very effective against emerge anytime during the growing sea- because natural enemies keep its popula- them; however, land with permanent son. Germination is strongly enhanced tion low. When the plant was introduced cover (pasture, range, roadway ditches, by light. Optimum germination occurs in into North America, its natural enemies and wasteland) that is not managed to moist soils at 59° to 68° F in light and 68° were left behind. Without these natural prevent bare ground is more likely to to 86° F in the dark. Probably the most checks, the thistle is able to thrive and develop a serious infestation. common life cycle is for musk thistle to • In pasture and rangelands germinate in the summer, overwinter as thistles compete for the mois- a rosette, and begin bolting (seed stalk ture, sunlight, and nutrients production) about May 1. A musk thistle needed to produce forage for rosette is a cluster of leaves in circular livestock. Musk thistle is not form that grows flat on the ground a poisonous plant; however, without an upright stem (Figure 2). A livestock will refuse to enter bolted plant is one that has developed an heavily infested areas and will upright stem (Figure 3). not graze close to the spiny Blooming starts with the terminal plants (Figure 1). head at the top of the plant about the first • On roadways and wastelands week in June and progresses to the lower musk thistle does not provide branches over six to eight weeks.Musk sufficient protection against thistle is a prolific seed producer. Large, soil erosion, crowds out desir- extensively branched plants in sparse able vegetation, is unsightly, stands may have 100 or more heads with hinders movement of people a total production of about 20,000 seeds. and wildlife, and produces The main terminal heads on the upper seed that infests surrounding branches bear the bulk of the plump, areas. well-filled seeds. Individual terminal Figure 1. Dense patch of musk thistle. heads can have as many as 1,500 seeds, each a little over 1/8 inch long (Figure 4). Seed germination may run as high as 95 History percent shortly after dissemination and most germinate in the first year; none- arly American records are scarce and give little clue as to when and where musk thistle first theless, some will remain viable for more Ebecame established on this continent. The earliest known collections were made from 1852 to than 10 years in the soil. 1869 by T. C. Porter near Harrisburg, Pennsylvania. Seeds are dispersed by wind, small mammals, birds, and water. A field study Musk thistle, also known as nodding thistle, is now naturalized throughout most of the United on the effects of wind speed on musk States and southern Canada. It occurs from Nova Scotia west to British Columbia, south to California, thistle seed dispersal showed that seed and east to Georgia. attached to pappus can travel up to 330 feet at wind speeds of 12 miles per hour In Nebraska, musk thistle was not found in extensive plant collections made during the late (Figure 5). A computer model based on 1920s and 1930s; however, in 1932 a specimen was brought to a field day in Seward County for this field trial indicates that less than 1 identification. It was recorded near Dawson in Richardson County during a 1940-41 botanical survey. percent of musk thistle seeds are blown more than 330 feet, and more than 80 These scattered reports, references, and collections indicate that sometime between 1945 and 1950 percent of seeds are deposited less than musk thistle emerged as a weed species of economic importance in Nebraska. By 1959 it was such 130 feet from the release point. Less than a pest in eastern Nebraska pastures and waste areas that the Nebraska Legislature declared musk five percent of seed remains attached to the pappus when it breaks from the 2 thistle a noxious weed and required all landowners to prevent seed production on their lands. flower head so most thistle pappus float- ing in the wind do not bear seed. Identification eaves of both rosettes and bolted plants L are deeply cut (segmented) and dark green with a light green midrib. There is a grayish-green area at the outer edge of each spine-tipped leaf segment (Figure 6). Each lobe has three to five points that end in a white or yellowish spine. The leaves extend onto the stem, giving it a winged or frilled appearance. The leaves and stem are relatively free of hair. Seedlings emerge with two cotyledon leaves, then add other Figure 2. Musk thistle rosettes can smother other vegetation. Figure 3. Musk thistle in early bolting stage. leaves one leaf at a time to develop into a rosette that can reach over 2 feet in diam- eter. Mature plant heights are typically 5 to 7 feet with a long, fleshy taproot. Musk thistle has deep reddish purple flowers that are large (up to 3 inches in diameter) and attractive. The head is sol- itary on the end of the stem and nods or hangs down as it grows in size (Figure 7). A close relative, the plumeless thistle (Carduus acanthoides L.), is also found in Nebraska. The general appearance of plu- meless thistle is similar to musk thistle (Figure 8). The distinguishing character- istics are that plumeless thistle heads are smaller and plumeless leaves are more deeply cut with sparsely to noticeably Figure 4. Musk thistle seeds are light tan. One Figure 5. Musk thistle seeds are dispersed by windblown hairy areas, particularly along the leaf plant produces 10,000 to 20,000 seeds. pappus. veins and stems (Figure 6). Figure 6. Leaves of musk thistle (left) Figure 8. Plumeless thistle (left) and musk thistle (right) in early and plumeless thistle (right). Musk thistle bloom. Note the nodding heads of musk thistle. leaves have a light green midrib, are Figure 7. Musk thistle flower heads are pink to grayish green on the outer edge, and are purple and showy. relatively free of hair. 3 production is increased. Cultural control only when needed and at rates based on methods include: soil tests so the fertilizer is used by the Control Methods • maintaining desirable plants that are desired plants in late spring and sum- usk thistle will be a part of Nebraska’s vigorous and competitive; mer. Most musk thistle germinate in the Mflora for the foreseeable future and • preventing seed from getting into the late summer and fall, so avoiding higher will continue to infest areas that are not area; soil fertility during this time of year will managed to prevent invasion. • maintaining a good soil fertility reduce growth. A management plan should include program; Multispecies grazing works well to a combination of cultural, mechani- control many of the plants that cattle do • using controlled multispecies grazing cal, chemical, and biological control not like to eat. Some producers claim (grazing with cattle, sheep, goats, etc.), methods. Its primary goals should be to that goats, horses, and donkeys will graze and conducting prescribed burns. discourage establishment by encourag- on musk thistles; however, no research is ing vigorous competition of the desirable A vigorous, thick perennial plant available to confirm these claims. species and to prevent seed production community is a difficult place for musk Prescribed burning does not directly by existing plants. Most pasture weeds thistle seedlings to establish. A well man- control musk thistle but can make other gain their foothold because the desirable aged pasture produces more forage and control methods more effective. It is species are overgrazed. County Weed competes vigorously with the few weeds important to burn at the proper time to Control Authorities enforce the Noxious that do get established. Researchers have promote vigorous grass growth and to Weed Law through survey, notification, found that musk thistle growing in an apply a herbicide about 10 to 14 days after and supervision of control efforts. Most area where surrounding vegetation had the thistles have recovered and are grow- thistles growing in a pasture likely origi- been removed produced 10 times as ing well. Prescribed burning may stimulate nated from seed produced nearby. many flowering heads and grew almost new grass seedlings and tillers which can twice as tall as thistles in an average thicken the grass and increase competition Cultural pasture. The backbone of a good control against musk thistle in future years. Cultural controls often provide a program is encouraging vigorous growth win-win situation for the land man- of desirable plants. Mechanical Excess soil fertility can aid musk this- ager and livestock: musk thistle and Mechanical control such as hand dig- tle seedling establishment. Use fertilizer other weeds are controlled and forage ging, cutting heads, mowing, or shred- ding is effective after the musk thistle has reached the bud or bloom stage.