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PNW 105 • Revised July 1994 Field Horsetail and Related Species Equisetaceae L.C. Burrill and R. Parker T he Horsetail (Equisetaceae) patches or can lead to family comprises 30 species, all new infestations in the ancient genus Equisetum. when root segments During the Carboniferous age are transported. (more than 230 million years Horsetails and ago), the Horsetail family was scouring rushes are the dominant plant group in the found most often in world, with plants reaching wet to moist areas, gigantic size. Two basic forms but once established of horsetails survive today. One they can grow well in is the hollow, jointed, and leaf- moderately dry areas. less scouring rush. The other is the horsetail with whorls of Field Horsetail slender, green, jointed branches (Equisetum around hollow, jointed stems, arvense L.) often occurring in great num- bers, giving the appearance of a Two types of stems horse’s tail. grow annually from Because the stems may be- dark, creeping, come encrusted with minute brown-woolly, tuber- particles of transparent silica, bearing rootstocks all of these plants often are (rhizomes). Tan-col- named “scouring rushes.” The ored fertile stems name arose from the use of emerge in early these plants by the pioneers as a spring and reach a scouring agent for pots and height of 1 foot. These pans. They also are reported to unbranched stems are Figure 1.—Field horsetail. be equivalent to the finest brittle, resemble small grades of steel wool in polish- asparagus sprouts, ing wood finishes and were launching the spores from the and end in a spore-bearing cone formerly standard items with cone into the wind. This is an which may be up to 4 inches European cabinet makers. important method by which long. The fertile stems lack chlo- Several species of horsetail these plants spread to new sites. rophyll and die back shortly and scouring rush are found in Spores eventually produce after the pale-green spores are the Pacific Northwest. They are new plants that send branches shed. Fertile stems are rare com- perennial, non-flowering plants downward into the soil. They pared to the sterile or vegetative that reproduce by spores. The establish successive, horizontal stems. spore-producing portion (cone) rootstock (rhizome) systems at of the plant contains thousands about 12-inch intervals as Larry C. Burrill, Extension weed of dust-like spores equipped growth continues downward. specialist, Oregon State University; with spring-like appendages This profuse and deep root sys- and Robert Parker, Extension weed that uncoil as the spores dry, tem can extend the borders of scientist, Washington State University. A Pacific Northwest Extension Publication • Oregon • Idaho • Washington Sterile stems emerge after the Horsetail is poisonous to ani- coordination; and difficulty in fertile stems and may reach a mals, particularly horses, when turning. The appetite remains height of 2 feet and die down in eaten in large quantities. Hay normal until just before death. the autumn. These stems are containing 20 percent or more Attempts to work or exercise tough and wiry, with whorls of horsetail produces symptoms in poisoned horses produce numerous four-angled green horses in 2 to 5 weeks. trembling and muscular branches (modified leaves) Symptoms include exhaustion. coming from the joints to form unthriftiness, followed by In late stages, muscular rigid- bushy plants. Ten to 12 ridges weakness, especially in the hind ity and constipation may be run up and down the stem, quarters; lack of normal noted. In fatal cases, death is compared with the more nu- preceded by quiescence and merous (20 to 40) but smoother coma. ridges on stems of giant horse- Removal of the tail (E. telmateia). contaminated forage in the 1 Fleshy, tuberous growths, ⁄4 early stages of poisoning 3 to ⁄4 inch in diameter, are brings about rapid arranged singly or in pairs on recovery. Horsetail the rhizomes at numerous poisoning is rarely fatal to joints. These tubers store plant cattle or sheep but usually sugars (carbohydrates) and are results in a loss of located from a few inches to condition. more than 6 feet deep. Field horsetail may Carbohydrates are inhibit surrounding accumulated and stored after vegetation (allelopathy) about mid-May. The plant because of its alkaloid has a surprising content. Researchers in regenerative capacity Russia studied the effects because of the reserves in the of water extracts taken extensive root system. from field horsetail on seed germination and early growth of meadow grasses. Livestock Of 13 species tested, field horsetail displayed the Poisoning strongest inhibitory effect on seed germination and There are about seedling vigor after it had 20 species of been applied to 30 species Equisetum in the of grasses. Pacific Northwest Field horsetail is com- and all are con- Field horsetail left: tuber-bearing rootstock; mon throughout the Pacific sidered to be center: sterile shoot; Northwest and all of the toxic. Field right: fertile stem. United States except the south- horsetail is the eastern area. species that live- stock eat most often. Giant Horsetail Prevent spread and establish- (Equisetum telmateia Ehrh. ment of horsetails by using only var braunii (Milde) Milde) clean soil and planting material for ornamental settings. In Giant horsetail resembles certain situations, it may be field horsetail, but is taller reasonable to stop spore and more robust. It has more formation by destroying the numerous ridges on the veg- fertile stems before they etative stems than field horse- mature. Mechanical methods, tail and fertile stems are abun- flame, or herbicides are dant. Giant horsetail is found effective options. west of the Cascade summits Scouring rush The shoots are without func- in the Pacific Northwest. tional leaves, so the plants can- not tolerate much shading. Scouring Rush numerous weak branches Look for opportunities to re- (Equisetum hyemale L.) whorled around the duce vigor and growth with stems, but the spore- Scouring rush differs from shade from plants or synthetic producing cone on top shading fabric. the horsetails in that the stems distinguishes it from the are leafless, all are fertile, and For established patches, ef- leaf-bearing stage of field forts should be directed at de- they do not die back in the fall. horsetail. The stems resemble fertile pleting the food reserves in the stems of the horsetails, but rhizomes. Complete removal of they are green and have two the tops about 2 weeks after black bands at the joints. Each Control each emergence for 3 or 4 years should give good control. stem is topped by a spore- Cultural Control bearing cone. Stems reach 4 Horsetail stems are neither feet in height. Plants may be In field crops, strong nor sharp. Thus they are seen throughout the Pacific ornamentals, and effectively blocked by most of Northwest on banks of ditches landscaped areas, field the porous fabrics (geotextiles) or the edge of waterways and horsetail most often is the used in landscape and indus- reservoirs. Scouring rush can be problem from this plant trial sites. Layers of bark mulch, weedy but also is an attractive group. On roadsides and sawdust, or other plant material plant for certain garden uses. railroads, it usually is will not control horsetails. giant horsetail that is a When it is safe and economical Braun’s Scouring-Rush problem, while the to use it, controlled flame is scouring rushes are temporarily effective against (Equisetum laevigatum A. horsetail. Br.) problems on road-sides and in ditches or on their This plant is similar to banks. Each setting has Chemical Control scouring rush, but in the different opportunities and There are several herbicides Pacific Northwest it grows as restrictions for control of that give temporary or season- an annual and usually is Giant weeds. horsetail long control of the horsetails shorter than scouring rush. It Lasting control of the and scouring rushes. Few herbi- usually has one black band horse-tails is difficult to cides applied once provide last- around each stem segment, achieve because of the high ing control. Selection of a herbi- whereas scouring rush has two level of food reserves stored in cide depends on the crop or site bands. Braun’s scouring rush the rhizome. being treated. sometimes is found with Figure 3.—Giant horsetail often grows in areas where the ground has recently been disturbed. Since herbicide registrations change frequently, this publication doesn’t make specific recommendations. Refer to the Pacific Northwest Figure 2.—Scouring rush often grows on roadsides. Weed Control Handbook, revised and published annually by the Extension Services of Oregon State University, Washington State University, and the Photographs provided by Larry Burrill, Extension weed specialist, Oregon State University. University of Idaho. The black-and-white illustration was reproduced, with permission, from La Rea Dennis, Detailed instructions for Gilkey’s Weeds of the Pacific Northwest (Corvallis, OR, Oregon State University, 1980); © La herbicide use are provided on Rea J. Dennis. container labels and in other Pacific Northwest Extension Publications contain material written and produced for public distribution. You may reprint written material, provided you do not use it to endorse a literature provided by commercial product. Please reference by title and credit Pacific Northwest Extension manufacturers. Publications. To reproduce material used with permission on pages 2 and 3 in this publication, please contact the original source. Pacific Northwest Extension publications are jointly produced by the three Pacific Northwest states—Oregon, Washington, and Idaho. Similar crops, climate, and topography create a natural geographic unit that crosses state lines. Since 1949 the PNW program has published more than 450 titles. Joint writing, editing, and production have prevented duplication of effort, broadened the availability of faculty specialists, and substantially reduced the costs for participating states. Published and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914, by the Oregon State University Extension Service, O.E.

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