Common Name:  Downy Brome/ Cheatgrass
Latin binomial:  Bromus tectorum

by Meghan Trainor, Extension Weed Associate, MSU
     Alvin J. Bussan, Cropland Weed Specialist, MSU

[ Plant Identification | Distribution | Life History | Management Practices ]

Introduction

Downy brome (Bromus tectorum), also commonly known as cheatgrass and Junegrass, is an annual or typically a winter annual belonging to the Poaceae family.  It is a major problem in winter wheat and alfalfa in Montana.  

Plant Identification

Downy brome plants stand from 5 to 60 cm tall and are covered with soft hairs at all growth stages.  The stems of a mature downy brome plant grow in large tufts.  The flat leaves are 4 to 16 cm long, 2 to 4 mm wide, and light green. The ligules are membranous and short (3 mm).  Figure 1 illustrates the leaf sheath of a small downy brome plant.  Figure 2 shows the short ligule. 

Figure 1.  The leaf sheath and blades of a young downy brome plant.	Figure 2.  The ligule of a downy brome plant.

The spikelets are numerous, hairy, narrow (3/8 to ¾ inch long), and on slender curved threadlike branches.  Each spikelet has 3 to 7 florets.  The inflorescence is dense, slender, drooping, one-sided, and 2 to 6 inches long.  Downy brome awns are purple at maturity and measure 12 to 14 mm long.  The lemmas are toothed, measure 9 to 12 mm, lanceolate, and covered with long soft hairs.  The palea is shorter than the lemma. The seedhead of downy brome is shown in Figure 3.

In the seedling stage downy brome can be distinguished from other grasses by its very hairy leaves.  Also, fall rye can be confused with downy brome in the seedling stage because both plants are purplish.  However, fall rye has auricles whereas downy brome does not have auricles.  Auricles look like small hooks that encircle the stem at the base of the leaf blade.

As the heads develop, downy brome becomes easily identifiable because the plants have a silvery sheen and, as they mature, become reddish-purplish.  Figure 4 shows an infestation of mature downy brome plants.

The fibrous finely divided root system has only a few main roots (an average of 7).  Furthermore, downy brome reproduces by seed.

Bromus tectorum is distinguishable from other annual (B. secalinus, B. racemosus, B. japonicus) and perennial (B. inermis) species of Bromus by its slender stems, hairy leaves, and the long-awned (bristly) spikelets on twisted branches.  Also, B. tectorum matures 1 to 2 weeks earlier than other annual bromes (Upadhyaya et al. 1986). 

Figure 3.  Downy brome seedhead	Figure 4.  Mature downy brome plants.

Distribution

Downy brome was introduced to North America from the Mediterranean area of Europe sometime before 1861.  Its first recorded appearance was in wheat fields in Washington, Utah, and British Columbia.  Farmers began calling it cheatgrass because they felt that this outsider cheated them of their crops.  Since its introduction downy brome has spread throughout the continent.  Cheat seeds were spread across the West as they lodged in the hair of livestock, got mixed in with shipments of wheat seeds, and were dumped along railroad sidings when cattle bedstraw was thrown away. 

Common habitats of downy brome include overgrazed range, abandoned farmlands, around farm and ranch buildings, railroads, and roadsides.  Also, downy brome thrives under dry conditions.

Distribution Across Montana 

Downy brome occurs in all Montana counties.

LIFE HISTORY 

Germination 

Under field conditions, downy brome seeds germinate in fall, winter and spring.  Most seeds germinate within one year of maturation.  Constant late summer or late fall rains will cause rapid germination and abundant fall growth.  However, if adequate fall moisture is not available, downy brome can act like a spring annual.

Generally, the germination/establishment pattern reported for downy brome has been germination in the fall and then over-wintering as a seedling.  A study by Buman and Abernethy (1988) reports that downy brome produced high germination under broadly fluctuating temperatures, specifically 20–30° C for a 16 hour day and 5–10° C for an 8 hour night.  Field results support that downy brome had higher germination in the conditions in which there was a wide temperature fluctuation between day and night.  Germination was lower in the laboratory studies where a constant day-night temperature was maintained. 

Under laboratory conditions Hulbert (1955) found 95-96% germination after 11.5 years of storage.  When buried under the soil, these seeds lose their viability in 2 to 5 years (Wicks et al. 1971).  Furthermore, downy brome seeds can withstand temperatures ranging from 100 to 120 °C for one hour at low moisture content (9.8%) without losing viability (Maun 1977).  Other researchers (Richardson et al. 1989) have also found that water deficits did not affect seed weights or germination percentages.  These results indicate the ability of downy brome to tolerate high soil temperature.

Afterripening

Plant litter accumulation on the soil surface favors seed germination and seedling establishment (Evans and Young 1970).  Wicks et al. performed a study that showed downy brome seeds covered with soil germinated more rapidly than those on the soil surface (1971). 

Emergence 

Field studies have shown seedling emergence is greatest from soil depths of 2.5 cm or less.  Little or no emergence occurs below 10 cm.  Seed buried at 20 cm did germinate but did not emerge.

Under high moisture conditions, more seedlings emerged from coarse- soils than from fine-textured soils and from greater depths (Wicks et al. 1971).  A study by Thill et al. demonstrates that decreasing soil moisture potential decreases the percentage and rate of downy brome seedling emergence (1979).  Also, as soil compaction increased seedling emergence decreased.  However, soil compaction did not affect germination.

Persistence 

Downy brome seeds can survive in the soil for more than one season.  Thill et al. suggest this may be due to an environmentally induced dormancy (1984).  Researchers report that harvested seeds showed 95% germination in two weeks, whereas ungerminated seeds that underwent one over-wintering period germinated more slowly when brought to favorable conditions (Young et al. 1969).  Further studies show there is little or no primary seed dormancy in downy brome caryopses at maturation.  Rather, for its survival this weed seems to rely on some kind of environmentally induced dormancy.

Research at Montana State University has shown that under full no-till regimes, downy brome seed can remain fully viable for more than three years if it is deposited in thick plant litter on the soil surface.  In the past, under more rigorous tillage regimes, downy brome seed was completely buried.  Under these conditions, the seed will only germinate if it is wet enough for a sufficiently long time.  Under no till, the seed in trash does not remain wet enough long enough for it to germinate, thereby extending the period of viability (Wright and Fay 1995).

Crop Competition  

Downy brome is a serious weed on rangelands and in several agricultural systems.  Winter wheat, alfalfa, and grass seed fields are croplands in which downy brome has become of particular concern.

Because their growth habits are similar, downy brome is an even bigger threat to winter annual crops, namely winter wheat.  Weed density and time of emergence of the weed relative to the crop are two of the most critical factors affecting weed interference.

A study conducted over 3 years near Lethbridge, Alberta, showed that downy brome reduced wheat biomass up to 59% and seed yield up to 68% (Blackshaw 1993).  Notably, the time of downy brome emergence relative to wheat had a larger affect on yield loss than did the density of downy brome. 

Furthermore, at nearly the same densities, downy brome caused a 2- to 5-fold greater yield loss when it emerged within 3 weeks after winter wheat than when it emerged 6 weeks after wheat or in early spring.  Only at densities of 200 to 400 plants/m2 did late-emerging downy brome cause significant wheat yield or biomass losses. 

MANAGEMENT PRACTICES 

Prevention

Despite successful efforts to control downy brome in croplands -- infested rangelands, pastures, roadsides, and waste areas throughout Montana provide a continuing source of downy brome seed for reinvasion of winter wheat crops.  Seed spread is mainly through contaminated grain, hay, straw, manure and farm machinery.  The long awn attached to the seed helps it stick to animal fur, as well. 

To prevent initial infestation in cultivated land, ensure that any seed purchased is certified free of downy brome and thoroughly clean equipment, especially swathers and combines.

Four main reasons are cited as to why downy brome has become more of a major problem in cultivated land.

1. Farmers are re-cropping more, thereby not allowing for the opportunity to break up the downy brome life cycle.

2. The shorter wheat varieties used today allow more light to penetrate the crop canopy, making downy brome more competitive.

3. More fertilizer is used each year giving downy brome a competitive edge.

4. Farmers rarely use the mold-board plow and are instead using variations of either stubble/mulch tillage or no tillage at all.  The chisel plow doesn’t invert soil, and as a result, downy brome seed is no longer buried deeply.  In no-till farming, downy brome seed remains on the soil surface which is the preferred environment of this plant since it is a surface germinator.  It thrives under no-till production.  Shallow burial, or surface germination, is the ideal germination environment for downy brome (Wright and Fay 1995).

Cultural Control 

Cropland Weed Specialist, A.J. Bussan at MSU in Bozeman, says the first key to successful control of downy brome it to select appropriate fields.  Crop rotation is the principal management strategy for downy brome.  For example, downy brome populations increased from 2 up to 60 plants per ft² after 3 years of continuous winter wheat in research trials.  In contrast, winter wheat - fallow or winter wheat - canola rotations maintained downy brome populations below 10 plants ft² in the same study.  As a result, a number of Montana growers have adopted a 3 or 4 year rotation that alternates spring crops with winter wheat and fallow.  In selecting fields for planting winter wheat, growers should select fields where the downy brome has been effectively cleaned up by crop rotation.

Another approach involves timely summer fallow tillage.  The major cause of the downy brome problem is annual seed production.  Timely summer fallow tillage will break this cycle.  Downy brome matures quickly in the spring (hence the weed’s other common name Junegrass).  Therefore, summer fallow tillage must occur early enough to prevent seed production.  If seed heads emerge from a downy brome plant before tillage or after tillage, viable seed will be produced and must be dealt with in the fall prior to seeding winter wheat. 

Pre-plant control is another effective strategy.  The most common technique used by Montana farmers to control downy brome is to delay winter wheat seeding in the fall until rains occur.  This stimulates germination of downy brome seed which is easily controlled during winter wheat seedbed preparation.  Bussan suggests preparing a firm seedbed 2 weeks prior to planting.  The tillage and mixing of wet and dry soil can stimulate downy brome seed to germinate and emerge.  The emerged downy brome can be managed by additional tillage or herbicide application prior to planting.  Popular herbicides for pre-plant management include Roundup or Gramoxone Extra.  Both products can be applied after planting, but before crop emergence, as well.  Roundup and Gramoxone Extra should be applied with ammonium sulfate.  Be sure to follow the label for proper rates.

For growers with limited or no-till cropping systems, stale seed bed techniques may not fit.  However, using a Phoenix or spring-toothed harrow prior to planting may stimulate emergence, in particular if rain occurs prior to planting.  In addition, growers could use stale seedbed techniques on field edges or in problem areas where downy brome is likely to occur to prevent its spread across fields.   

Narrow row spacing of winter wheat reduces the competitive ability of downy brome.  However, this is not a feasible practice in the dryer areas of Montana due to increased competition among wheat plants for moisture. 

For those farmers who anticipate a downy brome problem, increasing the seeding rate of winter wheat can be an effective technique.  Increasing the seeding rate of winter wheat creates more competition for the downy brome plants. 

Downy brome evolved in a rangeland situation and is therefore adapted to that type of environment.  Thus, the seed germinates easily on the soil surface, but less effectively when buried.  Researchers in Washington report that firmer seedbeds allowed fewer downy brome seedlings to emerge. 

Since downy brome grows along roadsides, it serves as a source of seed which can infest adjacent cultivated land.  The summer fallowing pattern of cultivated land can eliminate much of the downy brome seed that’s produced along the borders of fields.

Biological Control 

The studies on potential biological controls of downy brome have mainly focused on downy brome in a rangeland environment.  One such study looked at potential biological control of downy brome with crown and root rot fungi.  The researchers suggested that crown rot might be a potential biological control on downy brome in the arid western U.S. because it is adapted to dry soils and has low virulence on desirable grasses, such as wheatgrass (Grey et al. 1995).  Thus, crown rot causes greatest damage on moisture-stressed plants and results in susceptible disease reactions on downy brome.

Mechanical Control 

Neither mowing nor burning are effective controls to prevent seed set.  Seed will continue to mature on cut-off plants.  One option is mowing and removal of plants from the field.  Burning is not effective, as many of the seeds drop to the ground before the heat can kill them.  

As discussed above early spring tillage of fallow ground, tillage prior to planting spring-season crops, and tillage operations that bury downy brome seeds (mold-board plowing) are effective mechanical methods.

Chemical Control 

Herbicide programs have been developed for downy brome control in alfalfa, perennial grasses grown for seeds, and for some rangeland plants.  In winter wheat, however, chemical control is difficult due to the species having similar growth habits and susceptibility to herbicides.

The herbicides that control downy brome include atrazine, bromacil, cyanazine, chloropropham, diclofop, glyphosate, metribuzin, paraquat (with or without selected triazines), pronamide, propham, simazine, terbacil, and trifluralin (Wicks 1984; Pepper 1984; Swan and Whitesides 1988). 

In Winter Wheat
Treflan (trifluralin) and Hoelon (diclofop) are applied before seeding winter wheat in the fall.  Research results at MSU have shown from 50 to 80% control of downy brome with Treflan.  Take care to place the seed below the Treflan-treated soil or crop injury will occur.  Treflan is sprayed onto a clean soil surface and incorporated with tillage equipment to a depth of one to two inches.  Seeding is done with a deep furrow drill to ensure that winter wheat seed is placed well below the treated soil.

Hoelon is also labeled for control of downy brome in winter wheat.  The rate of application varies with soil texture, soil organic matter content, soil moisture, and the expected downy brome density.  Due to Hoelon’s immobility in soil, it must be mechanically incorporated to a maximum of two inches deep within 48 hours after application, followed by a second incorporation prior to seeding.  

Sencor is a foliar-applied herbicide for downy brome control that is less effective than Treflan.  Sencor is applied in the spring after the winter wheat has more than 4 tillers and after secondary roots are longer than one inch.  Before applying Sencor, remove winter wheat plants from the soil and look to see if secondary roots have formed.  If Sencor is applied before secondary root formation, crop injury may occur.  Downy brome plants beginning to form tillers will not be controlled by Sencor (Wright and Fay 1995).  Furthermore, because some winter wheat varieties are sensitive to Sencor, check the label prior to application.

Roundup has shown to be the most effective herbicide for downy brome control.  Used during the summer fallow season, Roundup must be applied prior to heading of downy brome.  Downy brome can head out as early as May 1 in a warm spring.  Thus, in order to prevent seed production downy brome must be sprayed with Roundup either in the fall or in the very early spring.  Using Roundup is a more consistent control method than tillage because tillage will not kill downy brome if the conditions remain wet.

Selective herbicides for downy brome are available such as Maverick®, Far-Go®, Amber® and Finesse®.  Refer to all labels for specific information regarding proper rates and usage.

In Alfalfa
Several herbicides control downy brome in alfalfa.  Sencor, Lexone, Velpar, and Treflan will control it in the fall if applied to dormant alfalfa.  These herbicides will be most effective if applied in the fall than in the early spring because downy brome continues to grow slowly during the winter.  In other words, downy brome is more sensitive to these herbicides in the fall than in the spring.

As with all herbicides, read the labels carefully to ensure the proper use and safe application of all chemicals.

[ Plant Identification | Distribution | Life History | Management Practices ]

For more information regarding downy brome contact A.J. Bussan, Cropland Weed Specialist, at abussan@montana.edu .

Acknowledgements

Figures 1, 2, 3, and 4 are courtesy of the Weed Science Society of America's (WSSA) Photo Herbarium.

Literature Cited

Blackshaw, Robert E.  1991.  Control of Downy brome (Bromus tectorum) in conservation fallow systems.  Weed Technology. 5:557-562.

Finnerty, D.W. and Klingman, D.L. 1961.  Life cycles and control studies of some weed bromegrass.  Weeds 10: 40-47.

Grey, W.E., P.C. Quimby Jr., D.E. Mathre, and J.A. Young.  1995.  Potential for biological control of downy brome (Bromus tectorum) and medusahead (Taeniatherum caput-medusae) with crown and root rot fungi.  Weed-technol. 9 (2): 255-259.

Hulbert, L.C. 1955.  Ecological studies of Bromus tectorum and other annual bromegrasses. Ecol. Monogr. 25:181-213.

Maun, M.A. 1977.  Response of seeds to dry heat.  Can. J. Plant Sci. 57:305-307.

Pepper, T.F. 1984.  Chemical and biological control of downy brome (Bromus tectorum) in wheat and alfalfa in North America.  Weed Sci. 32: 18-25.

Richardson, J.M., D.R. Gealy, L.A. Morrow. July 1989.  Influence of moisture deficits on the reproductive ability of downy brome (Bromus tectorum).  Weed Science. 37 (4): 525-530.

Swan, Dean G. and Ralph E. Whitesides.  1988.  Downy brome (Bromus tectorum) control in winter wheat.  Weed Technology. 2: 481-485.

Upadhyaya, Mahesh K., Roy Turkington, and Douglas McIlvride.  July 1986.  The Biology of Canadian Weeds.  Bromus tectorum L.  Can. J. Plant Sci. 66:689-709.

Wicks, G.A., O.C. Burnside, and C.R. Fenster.  1971.  Influence of soil type and depth of planting on downy brome seed.  Weed Sci. 19: 82-86.

Wicks, G.A. 1984.  Integrated systems for control and management of downy brome (Bromus tectorum) in cropland.  Weed Sci.  32: 26-31.

Wright, Josette and Pete Fay.  1995.  Montana State University, Bozeman, Extension Publication.