Perennial Sowthistle (Sonchus
arvensis L. ssp. arvensis) FamilyFamily: Compositae (Asteraceae) Description and VariationDescription and Variation: A deep-rooted perennial herb, perennial sowthistle has erect, hollow stems with bitter, milky juice. The stems, which can be 1 1/2 to six feet tall, branch only at the top of the plant. The alternate leaves are variable in size with prickly edges and pointed lobes. The stem leaves are clasping and without stalks. The bright yellow flowers occur in heads that can be 1 1/2 to two inches wide when in full bloom. The flowers, which have five small teeth across the outer end, open two to three hours after sunrise and close around noon. The bracts beneath the flower are green and bristly with sticky hairs. A plant may have 20 heads during the flowering season from June to September, but usually only a few flowers at the same time. The oblong, dark-reddish seeds have five lengthwise ribs and a tuft of white, silky, parachute-like hairs that can carry it in the wind. Economic ImportanceEconomic Importance: Detrimental - Classified as a noxious weed in many states and provinces, perennial sowthistle is a problem in several crops, where it causes economic losses due to reduced crop yields, increased cultivation and herbicide expenses, and land depreciation. At high densities (27 shoots/m2), it has reduced spring wheat yields up to 45 percent in North Dakota. Perennial sowthistle is also a host of several economically important plant pests (Lemna and Messersmith 1990). Beneficial Beneficial - The plant makes acceptable
livestock feed and is excellent feed for rabbits and other foraging animals. In addition,
the roasted roots have been used as a coffee additive or replacement, and the young leaves
can be used in salads. The plant may have potential for use in oil or hydrocarbon
production, since most of the latex is composed of oil. The plant is also a source of
pentacyclic triterpenes, which may have use in the pharmaceutical industry (Lemna and
Messersmith 1990). Geographic DistributionGeographic Distribution: A native of Eurasia, perennial sowthistle is distributed from Scandinavia south to Italy and east to the western portions of the former Soviet Union. Since its introduction to North America, it has spread widely throughout the northern United States and southern Canada. The plant has also established in South America, Australia, and New Zealand. Widely established in temperate regions, it is not found in the tropics (Lemna and Messersmith 1990). HabitatHabitat: While it is adapted to many soil types, perennial soil thistle seems to prefer low, fine-textured soils, especially loams. The plant does better under alkaline or neutral conditions than under acidic conditions. Perennial sowthistle is commonly found in cultivated fields (both grain and row crops), waste areas, meadows, sloughs, woods, lawns, roadsides, beaches, ditches, and river and lake shores (Lemna and Messersmith 1990). HistoryHistory: A native of Eurasia, perennial sowthistle has spread to many parts of the world via seeds and roots (Gaines and Swan 1972). It was probably introduced to North America via contaminated commercial seed (Dennis 1980; Lemna and Messersmith 1990). The North American sighting of the species was from Pennsylvania in 1814. Growth and DevelopmentGrowth and Development: As the name indicates, perennial sowthistle is a perennial plant. In established stands, shoots and new roots begin to form around April, when the soil warms. The shoots develop from buds that overwinter on roots or the basal portion of aerial stems. Seeds also germinate around the same time period. Plants form rosettes early in development, which provide a large photosynthetic area. The species can spread rapidly via its spreading root system. Most plants do not flower during the first-year, but seedling growing under favorable conditions have been known to produce flowers in some areas (Lemna and Messersmith 1990). ReproductionReproduction: Perennial sowthistle reproduces by seeds and creeping roots (Muenscher 1955). Its root system allows the plant to quickly establish in new areas and to persist under cultivation. Seed production is highly variable, but a typical head produces roughly 30 seeds, which are generally dispersed by wind. However, the hairs (pappus) on the end of the seeds have hooked cells that allow them to stick to clothes, fur, vehicles, and farm implements. The seeds are also sometimes moved as commercial seed or hay contaminants (Lemna and Messersmith 1990). Response to HerbicidesResponse to Herbicides: Herbicide control of perennial sowthistle is better when combined with other control methods because the species is relatively resistant to many common broadleaf herbicides. Most chemical control recommendations for perennial sowthistle are for auxin-type herbicides. Amitrole, dicamba, MCPA amine, and 2,4-D amine have all been recommended for control at various growth stages (see Lemna and Messersmith 1990 for more details). Less information exists for non-auxin herbicides. Pre-harvest treatments of glyphosate have been successful in Britain, but fall applications were generally less effective than auxin-based herbicides. The species has also been shown to be susceptible to atrazine, simazine, bromacil, monuron, and diuron, as well as some sulfonylurea herbicides (Lemna and Messersmith 1990). Response to Mechanical MethodsResponse to Mechanical Methods: Depending on the timing and type, tillage can reduce perennial sowthistle stands. Some existing evidence suggests that mowing would not be as effective as tillage as a control method. Tillage at the seven to nine leaf rosette stage seems to work best for reducing the reproductive capacity of the roots. Depth of burial and amount of root breakage determine the effectiveness of tillage. Root fragments left on the soil surface die from desiccation, and those buried 30 cm or more are unlikely to resprout. However, roots buried at intermediate depths will produce new shoots. Smaller root fragments produce fewer, less vigorous shoots (Lemna and Messersmith 1990). Biocontrol PotentialsBiocontrol Potentials: Domestic animals - Since perennial sowthistle is palatable to both sheep and cattle, pasturing infested land can be an effective control method (Lemna and Messersmith 1990). Insects - In Europe, 53 insects are known to feed on perennial sowthistle. However, only six of these species are restricted to the genus Sonchus; this group includes four species that are endophytic in flower heads, one species extern on stems and leaves, and one species endophytic on leaves. In Canada, three insects have been investigated for biocontrol of perennial sowthistle: Tephritis dilacerata Loew (Diptera: Tephritidae), Liriomyza sonchi Hendel (Diptera: Agromyzidae), and Cystiphora sonchi Bremi (Diptera: Cecidomyiidae) (Peschken et al. 1989). Infestations of C. sonchi in Canada have produced no observable reductions in weed population sizes (Lemna and Messersmith 1990). No insect biocontrol agents are presently available for perennial sowthistle in Washington. Nematodes - Perennial sowthistle is susceptible to at least three species of nematode: Meloidogyne incognita (root-knot nematode), Heterodera sonchophila (cyst-forming nematode), and Pratylenchus penetrans (lesion-forming nematode). P. penetrans is pathogenic to several crops, but H. sonchophila is considered a specialized parasite that has been highly pathogenic to perennial sowthistle seedlings in Estonia (Lemna and Messersmith 1990). Microorganisms - Microorganisms - The plant is also susceptible to several fungi, viruses, and bacteria. Unfortunately, many of these pathogens cause disease in economically important crops, as well. However, three species of fungi (Marssonina sonchi, Septoria sonchi-arvensis, and Septoria sonchifolia) are apparently specific to perennial sowthistle in Canada (Lemna and Messersmith 1990). ReferencesReferences: *Anonymous. 1981. Weeds of the North Central States. North Central Regional Research Publication No. 281. University of Illinois Urbana-Champaign, Urbana. Bell, A.R., J.D. Nalewaja, S. Alam, A.B. Schooler, and T.S. Hsieh. 1973. Herbicide response and morphology of interspecific sowthistle crosses. Weed Science 21: 189-193. *Bell, A.R., J.D. Nalewaja, and A.B. Schooler. 1973. Response of perennial sowthistle selections to herbicides. Crop Science 13: 191-194. *Cronquist, A. 1955. Vascular Plants of the Pacific Northwest. Part 5: Compositae. University of Washington Press, Seattle. *Dennis, L.J. 1980. Gilkey’s Weeds of the Pacific Northwest. Oregon State University Press, Corvallis. *Gaines, X.M. and D.G. Swan. 1972. Weeds of Eastern Washington and Adjacent Areas. Camp Na-Bor-Lee Association, Davenport, WA. *Hakansson, S. and B. Wallgren. Experiments with Sonchus arvensis L. II. Reproduction, plant development and response to mechanical disturbance. Swedish Journal of Agricultural Research 2: 3-14. *Hakansson, S. and B. Wallgren. 1972. Experiments with Sonchus arvensis L. III. The development from reproductive roots cut into different lengths and planted at different depths, with and without competition from barley. Swedish Journal of Agricultural Research 2: 15-26. Hulbert, H.W., J.D. Remsberg and H.L. Spence. 1930. Controlling perennial weeds with chlorates. Journal of the American Society of Agronomy 22: 423-433. *Lemna, W.K. and C.G. Messersmith. 1990. The biology of Canadian weeds. 94. Sonchus arvensis L. Canadian Journal of Plant Science 70: 509-532. *Muenscher, W.C. 1955. Weeds (2nd ed.) Cornell University Press, Ithaca, NY. Pegtel, D.M. 1972. Effects of temperature and moisture on the germination of two ecotypes of Sonchus arvensis L. Acta Botanica Neerlandica 21: 48-53. *Peschken, K.P., A.S. McClay, J.L. Derby, and R. DeClerck. 1989. Cystiphora sonchi (bremi) (Diptera: Cecidomyiidae), a new biological control agent established on the weed perennial sowthistle (Sonchus arvensis L.) (Compositae) in Canada. Canadian Entomologist 121: 781-791. *Peschken, D.P., A.G. Thomas, and R.F. Wise. 1983. Loss in yield of rapeseed (Brassica napus, Brassica campestris) caused by perennial sowthistle (Sonchus arvensis) in Saskatchewan and Manitoba. Weed Science 31: 740-744. *Zollinger, R.K. and J.J. Kells. 1991. Effect of soil pH, soil water, light intensity, and temperature on perennial sowthistle (Sonchus arvensis L.). Weed Science 39: 376-384.
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