Common Groundsel Senecio Vulgaris L

PNW 466 • July 1994 Common Groundsel Senecio vulgaris L. S. Aldrich-Markham C ommon groundsel, native to Europe, is now common throughout the temperate re- gions of the world. It is wide- spread in Oregon, Washington, and Idaho, but most common west of the Cascade Mountains. This weed is found in many crops, including forages, cereals, mint, berries, and row crops, as well as in ornamentals and vegetable gardens. Groundsel is especially a problem in forage crops because it is toxic to livestock. The toxins are four pyrrolizidine alkaloids, which cause irrevers- ible liver damage. Some of the same alkaloids are found in tansy ragwort (Senecio jacobea L.), but tansy ragwort also con- tains two additional alkaloids that are more toxic. Poisoning occurs most com- monly in situations where animals cannot separate out the toxic plants—when they are mixed with the forage in a pasture, or when they are fed in hay or silage. The liver disease is chronic and progressive, re- sulting in death months later in most animals, with few or no Susan Aldrich-Markham, Extension agent, Yamhill County, Oregon State University. Figure 1.—Common groundsel grows from 4 to 18 inches tall. Leaves are deeply lobed with toothed margins. The lower stems and undersides of basal leaves usually are purplish-colored. A Pacific Northwest Extension Publication • Oregon • Idaho • Washington symptoms until 2 or 3 days be- hairy or woolly. Leaves have the base of the plant, becoming fore death. little or no leaf stalk, and are increasingly smaller toward the A lethal amount for cattle or arranged along the stem in a top. The plant has a nauseating horses is 7 percent of their body spiral. Basal leaves usually are odor when bruised. weight of groundsel or 5 per- purplish on the under surface, When small, woodland 1 cent of their body weight of 1 to 4 inches long, and ⁄2 to groundsel may be confused 1 tansy ragwort (for example, 50 1 ⁄2 inches wide. Stems are hol- with tansy ragwort, but it is an pounds fresh weight of ground- low and rather succulent. annual and does not form a sel or 35 pounds fresh weight of A similar species is woodland rosette of basal leaves in the tansy ragwort consumed by a grundsel (Senecio sylvaticus L.). first year like the biennial tansy 700-pound cow). This plant generally is larger, ragwort. Woodland groundsel 1 With lesser amounts, the liver growing up to 3 ⁄2 feet tall, with more often is found along roads loses function, but no symp- leaves more deeply lobed than and in disturbed areas in the toms may be apparent until the those of common groundsel. forest, while common ground- animal is stressed (by preg- Leaves are greenish gray and sel is a weed of fields and gar- nancy, a new feed, a different woolly. They are largest near dens and the waste areas toxin, etc.). Then the damaged nearby. liver may not be able to purify the blood fast enough, and death is sudden. Biology Sheep and goats have rumen bacteria that detoxify the alka- and Ecology loids, so they are able to con- sume twice their body weight Groundsel produces abun- of groundsel or tansy without dant seeds, which spread by liver damage. Grazing by sheep floating on the wind with their sometimes is used to control parachutes of hairs. One these weeds in pasture. groundsel plant can produce as many as one million seeds in a season. Groundsel is a hardy plant Identification that germinates over a wide Common groundsel is a range of temperatures. Plants member of the sunflower can survive cold temperatures (Asteraceae) family. The flower during the winter, then flower heads are numerous, with yel- and set seeds early in the grow- low disk flowers, but no ray ing season. March to April is flowers. The heads are cylindri- the primary period of bloom, 1 1 though plants flower through- cal, ⁄4 to ⁄2 inch long, with black-tipped bracts around the out the growing season. base. The seeds are slender, West of the Cascade Moun- 1 tains where winters are mild ridged, about ⁄2 inch long, and tipped with a tuft of silky white and wet, groundsel can flower hairs. all year, producing two or more The plant usually is a winter generations per year. annual, sometimes biennial, Plants growing under stress though it may germinate in all can produce seed when they are seasons. It grows from 4 to 18 only a few inches tall. Seed sur- Common groundsel plant, center. vival in the soil is short, and inches tall. The leaves are Flowerhead, leaf, and fruit on left are deeply lobed with toothed mar- with no dormancy period most Common groundsel; leaf and flowerhead seeds germinate within a year gins and may be smooth to on right are Woodland groundsel. or lose viability. Groundsel is People may carry weed seed Biological Control self-fertile; the flowers do not on clothing, vehicles, or equip- Larvae of the cinnabar moth, require cross-pollination. ment. Feeding livestock hay Tyria jacobaeae, an insect re- Common groundsel first was containing weed seed is another leased extensively in western found to have developed resis- source of infestation. Spreading Oregon and western Washing- tance to the triazine herbicides contaminated manure also ton for biological control of (atrazine, simazine) in Wash- spreads groundsel. tansy ragwort, also eat ground- ington in 1968. Triazines inhibit sel. These caterpillars are not photosynthesis by binding onto capable of significantly reduc- membranes within the chloro- Control ing a groundsel infestation, plasts in green cells. however, because they are Resistant groundsel plants present only from June through have an altered reactive site on Cultural Control August. the chloroplast membrane. This Research is being done in difference, while saving the Cultivation kills groundsel England with a rust fungus, plant from triazine damage, plants, and if done prior to seed Puccinia lagenophorae, which also results in chloroplasts that formation is an effective control provides a moderate level of are less efficient at gathering method. New plants, however, groundsel control. Leaf growth energy from light and fixing coming either from the reser- is impaired in infected plants, carbon from carbon dioxide voir of seeds in the soil or from and flower production is into sugars. In general, suscep- seeds blown in from adjacent reduced. Rust delays flowering tible plants are larger, flower areas, will establish readily in 1 to 2 weeks. earlier, and produce more seeds newly-cultivated soil. In order to be an effective than triazine-resistant plants. With alfalfa and other peren- control, the rust must be main- If a triazine herbicide is not nial forage crops, a dense and tained in the weed-infested used, a groundsel population vigorous stand competes area. One year without the will be dominated by suscep- strongly with weeds, so few presence of rust allows the tible plants. However, contin- new groundsel plants are able population level of groundsel ued application of the herbicide to survive the seedling stage. to revert to that of previous to a field removes competition Management practices that pro- years. The rust is unavailable from susceptible plants and mote vigorous crop growth can commercially. allows resistant plants in the reduce groundsel in a field. A population to increase. Triaz- thin crop stand leaves open ine-resistant groundsel popula- spaces for weeds to invade. Chemical Control Alfalfa is particularly suscep- tions have developed indepen- Several herbicides control tible to invasion by groundsel dently in many areas of the groundsel. Removing ground- when it is dormant in areas of country, including Oregon, sel from cereals and forage mild winters, or during alfalfa Washington, and Idaho. grasses is not difficult, but seedling establishment. If a removing it selectively from heavy weed population is ex- actively-growing forage le- pected, growers should pre- gumes is almost impossible. In Prevention irrigate to germinate weed alfalfa, herbicide applications seeds, then cultivate before Seed from groundsel plants can be made only during the seeding. growing along ditches, fence winter dormant season. In Frequent cutting reduces es- rows, roadsides, and adjoining mint, selective control with tablished alfalfa’s competitive land can be carried into fields herbicides is possible when the advantage and enhances condi- by wind. These seed sources groundsel is small. tions for weed invasion. Cutting should be controlled. Weed In order to prevent or delay alfalfa at longer intervals and seed also is carried into fields in the appearance of herbicide- avoiding late fall cuttings helps irrigation water and with con- resistant weeds, it is important keep alfalfa competitive. taminated crop seed. to avoid using herbicides that 1 1 Figure 2.—The flower heads are /4 to /2 inch long, with yellow disk flowers and black-tipped bracts around the base. Seeds are carried on the wind by a tuft of silky white hairs. have the same mode of action in the same field year after year. For information on which Figure 3.— A seedling plant of common groundsel. herbicides have the same mode of action, as well as further in- annually revised Extension formation on herbicide-resis- publication available from the tant weeds, refer to Extension Extension bulletin offices of publication PNW 437, Herbicide- Oregon State University, Resistant Weeds and Their Man- Washington State University, agement. and the University of Idaho. For suggested herbicides in Carefully read and follow label different cropping situations, directions when using any refer to the Pacific Northwest herbicide. Weed Control Handbook, an Photographs provided by Susan Aldrich-Markham, Extension agent, Yamhill County, Oregon State University. The black-and-white illustration was reproduced, with permission, from La Rea Dennis, Gilkey’s Weeds of the Pacific Northwest (Corvallis, OR, Oregon State University, 1980); © La Rea J.

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