Weed Technology. 1999. Volume 13:665-668

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Downy Brome, Bromus tectorum L. 1

LARRY W. MITICH2

INTRODUCTION AND ETYMOLOGY rum and refers to its abundance as a weed in areas where The genus Bromus in the Poaceae includes 100 spe­ cereal grains are grown. Pioneer farmers felt that were , des of annuals, biennials, and pere.nnials. Several spe­ being cheated in wheat yields by the weed and labeled it cheatgrass. Other common names include cheat cies are important as forage crops while others 'ate grown ' ' as ornamentals. It is distributed in the temperate areas downy chess, broncograss, and six-weeks grass (Sheley and in tropical mountainous re­ and Petroff 1999). Upon ripening, downy brome is a gions (Hyam and Parkhurst 1995). poor fodder crop because awns make it difficult and un­ Bromus tectorum L., downy pleasant for animals to eat (Zimdahl 1989). brome, an introduced annual, oc­ curs throughout inost of the U.S., DESCRIPTION Canada, and northern Mexico (Sheley and Petroff 1999). It was Downy brome is an erect annual, winter annual, or introduced to North America from biennial grass, growing from 5 to 60 cm tall, with only Europe before 1861. Downy brome a few main roots but a finely divided fibrous root system has a dual role as a serious weed and as an important penetrating to 30 cm deep. It frequently grows in large forage (Upadhyaya et al. 1986). tufts and is mainly self-pollinated, but out-crossing is Linneaus described Bromus tectorum in 1753. The ge­ also common (Hulbert 1955). neric name Bromus comes from the Greek bromos, an The stems are erect, slender, and mostly glabrous. The ancient name for oats, and broma or bromus for food as leaves are from 4 to 16 cm long, 2 to 4 mm wide, light the seeds were ground into flour (Hyam and Parkhurst green, and.;pubescent. Sheaths are separate except near 1995, Plowden 1970, Zimdahl 1989). In 1759, Benjamin the node at the bottom of each sheath, the lower ones Stillingfleet in his Biberg's Economy of Nature was the . pubescent and the upper ones sometimes glabrous. The first to use the common name brome for Bromus (Simp­ panicle ranges from 5 to 20 cm long, is rather dense, son and Weiner 1989). soft, and drooping, and is often pale green with a purple The specific epithet tectorum means "of the roofs" tinge. Branches are slender, pubescent, flexuous, with up (Latin tectum, roof); tector means straw for thatching to eight spikelets. Lemmas are toothed, 9 to 12 mm long, (Plowden 1970, Zimdahl 1989). In its original home in lanceolate, and are covered with long soft hairs. The Old World humid climates, downy brome was formerly awns, 12 to 14 mm long, are slender and straight. and extensively used to thatch house roofs (U.S. Forest Slender stems, hairy texture, and the long-awned Service 1937). spikelets in ·twisted branches distinguish Bromus tecto­ Most downy brome leaves have numerous fine hairs rum from other weedy annual bromes such as cheat that give them a soft, downy feeling when the plant is (Bromus secalinus L.), Japanese brome (B. japonicus green and growing actively, thus the common name Thunb.), and smooth brome (B. inermis Leyss.), a pe­ (Sheley and Petroff 1999). Downy (feathery; fluffy) was rennial. first used as specific names for plants such as downy oats by Ann Pratt in The Flowering Plants and Ferns of DISTRIBUTION Great Britain, 1854-1857, (Simpson and Weiner 1989). Although Bromus secalinus L. is called cheat, the From its Eurasian and Mediterranean ancestral home, common name, cheatgrass, is applied to Bromus tecto- B. tectorum has expanded throughout most of western and central Europe to southern Russia and western cen­ 'No. 66 of the series "Intriguing World of Weeds." tral Asia. It has been introduced to northern Europe, 2 Extension Weed Scientist Emeritus, Department of Vegetable Crops, University of California, Davis, CA 95616. North America, Japan, South Africa, Australia, and New

665 MITICH: DOWNY BROME

1930 downy brome occupied much of its current range, and by 1980 nearly every county in Montana, Idaho, and Wyoming had infestations (Mack 1981). Downy brome does not grow in wet places and sel­ dom appears at high elevations or in the more arid, west­ ern deserts. Although its occupation of certain areas may be a result of continued past overgrazing and depletion of better forage plants, it does not force out established native species from the range nor prevent their return (U.S. Forest Service 1937).

GROWTH AND DEVELOPMENT

Downy brome is generally considered a winter an­ nual, the young fall-germinated seedlings overwintering in a semidormant state and completing their life cycle the next spring. It may continue to grow through most of the winter, provided warm and moist conditions per­ sist. The roots continue to grow until spring, then their growth rate declines rapidly. However, it can become a Downy brome, Bromus tectorum L. spring annual if fall moisture is inadequate (Harris 1967, Klemmedson and Smith 1964). During ripening, downy brome plants turn purple and Zealand and in single localities in Iceland and Green­ then brown as they mature, but the leaves may assume land. In Scandanavia it is a lowland plant, but in the a purple tinge during winter dormancy. A sudden drop Alps it extends to an elevation of 2,000 m (Upadhyayay in temperature or a sudden drought can also cause purple et al. 1986). coloration that fades when growing conditions become Its introduction into North America occurred indepen­ more favorable (Stewart and Hull 1949). dently several times. Son utilized as ballast in ships sail­ Downy brome is a copious seed producer. It perpe­ ing from Eurasia into North America was one of the trates itself even during years with unfavorable growing original carriers of its seeds. The first downy brome in­ conditions (Sheley and Petroff 1999). Under good grow­ troductions probably happened this way in St. Louis, ing conditions, downy brome seed production can ex­ MO, about 1850 (Mack 1981). ceed 2.6 billion seeds/ha. Individual plants grown in high With the exception of Alabama, Georgia, South Car­ densities may produce about 25 seeds each; however, a olina, and Florida, downy brome is widely distributed solitary downy brome plant with plentiful tillers and throughout the U.S., including Hawaii (Hitchcock and grown with abundant moisture and sunlight can easily Case 1971). Although in the eastern U.S. it is only a produce 5,000 seeds (Young et al. 1987). Under range­ roadside weed, it is especially abundant in the West's land conditions, unterminated downy brome seeds usu­ Great Basin and Columbia Basin areas. Downy brome ally do not remain viable for longer than 1 yr (Hulbert occurs in all Canadian Provinces and extends into south­ 1955). ern Alaska and Yukon (Morrow and Stahlman 1984, The seeds are shed within a week after maturity and Pavlick 1995). wind disperses them short distances. They tend to blow Initial infestations were commonly found near rail­ along smooth soil surfaces rather than being carried in roads and wheat fields. Sowing wheat seeds contaminat­ the air. But the major ways of dissemination are in con­ ed with downy brome seeds was commonplace, and rail­ taminated grain, in discarded cattle bedding straw, in roads transported merchandise packed in straw infested transported cattle dung, in discarded straw packed with with downy brome. Train cars transporting livestock dry goods, and by farm machinery. Animals also aid in used straw as bedding, which was discarded along the seed dissemination because downy brome's long awn at­ railroad rights-of-way. Once introduced, downy brome taches to their hide, hair, and hooves (Hulbert 1955, spread to adjacent areas (Sheley and Petroff 1999). By Morrow and Stahlman 1984).

666 Volume 13, Issue 3 (July-September) 1999 WEED TECHNOLOGY

USES grow during winter, permitting it to invade a site before seedings of other species are established; downy brome Downy brome is one of the less palatable species of roots can grow at 3 C (Harris 1967). Bromus. Its early maturation, relatively sparse, hairy Dry downy brome greatly increases the rangeland fire leafage, and high ratio of unpalatable seed heads all hazard. It has extremely high flammability, permitting weigh a~ainst its usefulness. However, it grows on many poorer sites where more nutritional forage plants do not fires to kindle and spread rapidly, thus increasing the occur (U.S. Forest Service 1937). number and size of fires and control costs. Site distur­ Downy brome supplies the mass of early spring for­ bance caused by fire enhances its establishment and spread. Once established, it poses a greater fire hazard ~ge for all c~asses of livestock on grazing lands on many mtermountam ranges. It is undoubtedly the most impor­ than ·p~rennial grasses because of its early maturation; tant forage in this area because of the immense herbage perenmal grasses mature more slowly and remain green volume produced and the vast area covered. When uti­ longer. The water content also is lower in mature downy lized by livestock in the spring, downy brome supplies brome plants. It remains a fire hazard until the fall rains good-quality forage, but is production fluctuates exten­ begin. Fire decreases downy brome density substantially ,sively. It compares favorably in nutritional quality with in subsequent years (Stewart and Hull 1949). most native and introduced perennial grasses (Cook and In the better areas, where grazing is properly regulated Harris 1952). and fires are prevented, downy brome eventually tends Downy brome is ready to graze early in March on the to be largely replaced by more valuable and permanent lower mountain ranges, and remains tender and palatable perennial species (U.S. Forest Service 1937). until about the middle of May when it begins to mature Animals grazing nearly mature downy brome or con­ and turns reddish. A week or two later it dries complete­ suming it in hay are frequently injured. Its mature long ly and becomes straw colored. On the higher foothills it stiff awns easily puncture the lining in the mouth, throat, is grazed from April to early June. In the late summer and intestines of livestock, causing sores and infection, and early fall the less abundant but relished new growth reduction in food consumption, and subsequent weight appears. The livestock even consume some of the old loss (Upadhyaya et al. 1986). Sometimes the eyes of herbage is it is saturated thoroughly by late-season rains grazing livestock are also affected (U.S. Forest Service (U.S. Forest Service 1937). 1937). Because down brome establishes easily, has a shallow Although most downy brome seeds generally do not dense root system, and grows rapidly, it adds large survive longer than 1 yr on rangelands, its seeds may amounts of organic matter to the soil, aiding significantly remain viable for several years when stored dry within in erosion control (Upadhyaya et al. 1986). Dense un­ hay or straw bales. Transporting and feeding such bales grazed stands of it produce a litter layer which is very to livestock in uninfested areas spread the weed (Hulbert effective in conserving soil by preventing raindrop ero­ 1955). sion, promoting water infiltration, and preventing con­ centration of runoff into rills (Stewart and Hull 1949). LITERATURE CITED

Cook, C. W. and L. E. Harris. 1952. Nutritive value of cheatgrass and crested WEEDINESS wheatgrass on spring ranges of Utah. J. Range Manage. 5:321-337. Harris, G. A. 1967. Some competitive relationships between Agropyron spi­ Downy brome is a significant weed throughout North catum and Bromus tectorum. Ecol. Monogr. 37:89-111. Hitchcock, A. S. and A. Chase. 1971. Manual of Grasses of the United States. America, particular in alfalfa (Medicago sativa L.), grass · 2nd ed. New York: Dover Publications. 1051 p. seed fields, noncrop land, pasture lands, rangelands, and Hulbert, L. 1955. Ecological studies of Bromu:1 tectorum and other annual bromegrasses. Ecol. Monogr. 25: 181-213. winter wheat (Triticum aestivum L.). In some instances, Hyam, R. and P. Pankhurst. I 995. Plants and Their Names, A Concise Dic­ vegetation on overgrazed rangeland consists totally of tionary. Oxford, UK: Oxford University Press. 545 p. Klemmedson, J. 0. and J. G. Smith. 1964. Cheatgrass (Bromus tectorum L.). downy brome. It is the worst weed problem for winter Bot. Rev. 30:226-262. wheat growers in the western U.S. (Upadhyaya et al. Mack, R. N. t 981. lnvasioh of Bromus tectorum L. into western North Amer­ 1986). ica: an ecological chronicle. Agro-Ecosyst. 7: 145-165. Morrow, L. A. and P. W. Stahlman. I 984. The history and distribution of It is a successful weed because of its ability to utilize downy brome (Bromus tecrorwn) in North America. Weed Sci. 32:2-6. moisture from the soil's upper layers. Its root system Pavlick, L. E. 1995. Bromus L. of North America. Victoria, BC: Royal British allows most or all Columbia Museum. I 60 p. of the available moisture to be re­ Plowden, C. C. 1970. A Manual of Plant Names. New York: Philosophical moved from the upper soil profile. Its roots continue to Library. 260 p.

Volume 13. Issue 3 (July-September) 1999 667 MffiCH: DOWNY BROME

Sheley, R. L. and J. K. Petroff, eds. 1999. Biology and Management of Nox­ Upadhyaya, M. K., R. Turkington, and D. Mcllvride. 1986. The biology of ious Rangeland Weeds. Corvallis: Oregon State University Press, 428 p. Canadian weeds. 75. Bromus tectorum L. Can. J .. Plant Sci. 66:689-709 Simpson, J. A. and E.S.C. Weiner. 1989. The Oxford English Dictionary, 2nd Young, J. A., R. A. Evans, R. E. Eckert, Jr., and B. L.' Kay. 1987. Che~tgrass: ed., Volume 2. Oxford, UK: Clarendon Press. Rangelands 9:266-270. Stewart, G. and A. C. Hull. 1949. Cheatgrass (Bromus tectorum L.)-an eco­ Zimdahl, R. L. 1989. Weeds and Words. Ames, IA: Iowa State University logical intruder in southern Idaho. Ecology 30:5874. Press. 125 p. United States Forest Service. 1937. Range Plant Handbook. Washington, DC: U.S. Government Printing Office. 842 p.

Systems of Weed Control in Wheat in North America

The WSSA announces publication of the most comprehensive monograph ever published on wheat production practices and methods of managing weeds in wheat in the United States. Systems of Weed Control in Wheat in North America contains 22 chapters that total 487 pages and was prepared by 26 weed scientists who have specialized in weed management in cereals. The monograph documents spring and winter wheat production practices in different regions of North America, weed problems, and methods of managing weeds using her­ bicides and cultural practices. The monograph is divided into three parts. In the first part, the distribution of weeds of wheat in North America and yield loss assessment are summarized. In the second part, wheat production practices and weed control systems are reviewed for the following regions of North America: the Canadian Prairie Provinces, the Northern, Central, and Southern Great Plains, the Northeast, the Southeast, the Pacific Northwest, and California and Arizona. Finally, the use of the following herbicides in wheat is reviewed: barban, bromoxynil, clopyralid, diclofop, difenzoquat, flamprop, picloram, propanil, substituted triazines, triazinones, and urea herbicides, sul­ fonylurea herbicides, triallate, and trifluralin. Each chapter on wheat herbicides summarizes knowledge of weed control, application methods, spray additives, crop response, environmental effects on weed control, combi­ nation treatments, and environmental fate. This monograph summarizes weed control methods and research in wheat for the first time. Research con­ ducted over(the last 42 years is emphasized (1945 to 1989). The monograph should be useful to weed scientists, extension agents, other agriculturalists, crop consultants, farmers, and herbicide manufacturers, distributors, and sales personnel who are concerned with production of wheat. Systems of Weed Control in Wheat in North America may be purchased for $15.00. (Shipping charge: $3.50 for first copy; $0.75 for each additional copy.)

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668 Volume 13, Issue 3 (July-September) 1999