Taeniatherum caput-medusae
Encyclopedia
Taeniatherum caput-medusae is a species of grass
known by the common name medusahead. This aggressive winter annual grass is changing the ecology
of western rangeland
s in North America. Forty-eight percent of the total land area of the United States is rangeland, pastureland
, national park
s, nature preserves, and other wildlands. These lands are essential for agriculture
and for protecting the integrity of ecological systems. Natural areas contain many nonnative plant species
that occur as self-sustaining populations in the lower 48
of the United States, including medusahead. As of 2005, medusahead infested approximately 972700 acres (3,936.4 km²) in the 17 western states (from North Dakota
south to Texas
and west to the Pacific coast), and spreads at an average rate of 12% per year. As medusahead spreads, it outcompetes native vegetation, reduces land value, and creates a wildfire
hazard.
in 1903 as Elymus caput-medusae by Thomas Howell. Nevski recommended in 1934 that the Russian types of medusahead should be classified in a separate genus, Taeniatherum. In the 1960s, it was suggested by Jack Major of the University of California
that there are three geographic and morphologically
distinct taxa: T. caput-medusae, T. asperum, and T. crinitum. After traveling in Russia, Major thought the proper classification for the plant introduced to North America was Taeniatherum asperum. The genus was revised in 1986 by the Danish scientist Signe Frederiksen. He made the previously mentioned distinct taxa into subspecies
of Taeniatherum caput-medusae.
The subspecies caput-medusae is a native species to Europe, and is mostly restricted to Spain
, Portugal
, southern France
, Algeria
, and Morocco
. Subspecies crinitum is found from Greece
and the Balkans
east into Asia, and the range of subspecies asperum completely overlaps the other two subspecies.
In Asia, medusahead is widespread in Turkmenistan
, Iran
, Syria
, and in the northern portion of Israel
, inhabiting low mountains and plateau areas. It is both an agronomic
and rangeland weed
. It prefers soils rich in nitrogen
, and is often found on stony or gravelly soils. Carbonized seeds of this weed have been found in early agricultural archaeological site
s in Iran. Seeds were first found in strata
corresponding to the early days of sheep and goat
husbandry
.
native plants for moisture. It flowers in early spring, and by June or July its seeds, which are covered with tiny barbs, are mature. The barbs help the seeds attach to livestock, humans or vehicles that pass by. As the grass grows it accumulates silica, making it unpalatable to livestock except for early in its life cycle. It creates a dense layer of litter, and because of the silica content, the litter decomposes more slowly than that of other plants. This litter suppresses native plant growth while encouraging the germination
of its own seed, and after a few years it creates an enormous load of dry fuel that can lead to devastating wildfires.
Stands of medusahead vary in density from several hundred to 2,000 plants per square foot. This variance is directly related to annual precipitation
, soil type, and other vegetation in the area. Research has suggested that medusahead is highly adaptable and can produce more seeds at a density of one plant per square foot than 1,000 plants per square foot. Since it matures later than most other annuals, it is easy to identify as it is often bright green when the other annuals are brown. As it matures, it turns shades of purple and eventually tan.
Medusahead seeds disperse
relatively short distances and dispersal decreases as distance from the plant increases. Seeds are very well adapted for dispersal by adhesion to moving objects. The relatively long period of medusahead seed dispersal from July to October may be an adaptation to increase the likelihood of adhesion to animals.
s similar to those of wheat
or rye
. The lemma
s have long awns and the glumes have shorter ones, giving the seed head a layered look. As the awns dry, they twist and spread in all directions, similar to the snake-covered head of the mythological Medusa
. The barbs on the awns help the seed drive into the soil. The grainlike seed may remain viable in the soil for a number of years.
capacity of land infested with medusahead can be reduced by up to 80%. Wildlife habitat and biodiversity
also suffer, and the weed can eventually lead to alterations in ecosystem functions. The impact medusahead can have on species relying on sagebrush
is rarely mentioned. It can exacerbate the decline of sage-grouse
(genus Centrocercus) as it replaces plant communities that provide critical habitat for the bird.
Other species, such as mule deer
and chukar partridges
, tend to avoid areas overrun with medusahead because it is not a good food source. In the case of mule deer, a study in Oregon found that even though extensive stands of medusahead were available, those areas (when compared to other plant communities) were least preferred by feeding mule deer in winter, summer, and fall; and they ranked low in the spring. This decrease in feeding was related back to the dominance of medusahead, which deer do not eat, and the subsequent lack of forb
s. Chukar partridges will ingest medusahead seeds ( caryopses ) if given no other choice. However, if they are given free access to all the medusahead seeds they will eat, they suffered from a significant loss in body weight. Largely undamaged seeds were found in their droppings, suggesting that the digestibility of medusahead by the birds was low.
that combines two or more of the following methods.
chances for eradication increase dramatically.
. In some areas, more desirable plant communities came back after a fire, while in other areas medusahead continued to dominate after fire. There are a few guidelines that should be followed when burning medusahead. The burn should be conducted when the seed is in the soft dough stage (when the seeds exude a milky substance when squeezed) in the late spring. The initial fire should be one that is slow burning, something that is easily achieved by burning into the wind. This prevents the fire from advancing too rapidly and ensures that the current year's herbage is burned and periods of maximum temperature are long enough to kill medusahead caryopses. Viable medusahead caryopses are found almost entirely in the litter and on the soil surface.
Past studies on the effectiveness of burning may have given researchers false hope. The caryopses have severe temperature dependent afterripening requirements which prevent seeds from germinating at temperatures above 10˚C for about 180 days after maturity. If these conditions are met, many medusahead caryopses from the litter and soil in burned plots were viable. Since the seeds did not germinate during the afterripening period, researchers were misled into believing they were accomplishing more by burning than was actually the case.
can be effective if used in conjunction with other control methods. Glyphosate (Roundup) applied at 0.375 lbs/acre in the early spring before seeds are produced can provide good results. This timing will also limit the damage to nontarget species that develop later in the growing season. Research suggests that burning before chemical application is more effective than chemicals alone. In the late 1960s, a study was conducted that determined the effectiveness of paraquat
on medusahead control in different areas of the United States. This study found that paraquat was effective in controlling medusahead in California, but did not suppress the grass in Reno, Nevada
. This was significant because it determined that there was no effective herbicide for the simultaneous spraying and reseeding of medusahead infestations .
fungi including crown rot
and take-all
, but it was not susceptible to barepatch
, browning root rot, and common root rot. The diseases did not reduce the overall weight of the roots, but take-all significantly reduced the overall dry weight of the aboveground shoots. Soil-borne pathogens can have a severe effect on grasses as long as the environmental conditions for the diseases are optimized. Take-all is associated with plants growing in high soil moisture, and like crown rot, it affected medusahead. In contrast, crown rot had the greatest impact on water-stressed plants and therefore may be an effective biological control
of grassy weeds in the arid regions of the western U.S. It is also promising because it did not have a significant negative impact on desirable grasses such as western wheatgrass.
in the soil also has to be reduced. This usually takes two or three years, depending on soil moisture and growing conditions. After this, seedling of desirable species can become established. Combining a tillage
treatment followed by herbicide is most effective in controlling the weed and promoting desirable plant growth. Squirreltail
, bluebunch wheatgrass, crested wheatgrass
, intermediate wheatgrass
, Thurber's needlegrass, needle and thread
, Indian ricegrass, sandberg bluegrass
, and sheep fescue
are all competitive grasses that work well when renovating an area previously infested with medusahead in the western United States.
Plant communities that have high densities of large perennial bunchgrasses are more resistant to medusahead invasion, so managing rangelands to promote and maintain large perennial bunchgrasses is critical to prevent the spread of medusahead. This will reduce the establishment of new infestations, but successful management will also require searching for and eradicating new infestations. Controlling new infestations is more effective, and oftentimes more feasible, than trying to control large infestations.
Even if attempts to prevent and control new infestations are not entirely successful, these efforts will slow the rate of spread and give researchers and land managers more time to develop better prevention, restoration, and control methods. Also, slowing the rate of invasion helps promote rangeland health and productivity in areas that are most at risk of invasion. Without an active prevention program, this weed will continue to spread and increase its negative ecological and economical impacts. Managing medusahead may seem expensive per acre, but when all the acres that are protected by managing an infestation are considered, the price is very reasonable. And, when taking into account the rising land prices, the cost of medusahead management to the individual livestock producer is rapidly becoming more reasonable compared to purchasing additional acreage to offset production losses from medusahead invasion.
Poaceae
The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...
known by the common name medusahead. This aggressive winter annual grass is changing the ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
of western rangeland
Rangeland
Rangelands are vast natural landscapes in the form of grasslands, shrublands, woodlands, wetlands, and deserts. Types of rangelands include tallgrass and shortgrass prairies, desert grasslands and shrublands, woodlands, savannas, chaparrals, steppes, and tundras...
s in North America. Forty-eight percent of the total land area of the United States is rangeland, pastureland
Pasture
Pasture is land used for grazing. Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, cattle, sheep or swine. The vegetation of tended pasture, forage, consists mainly of grasses, with an interspersion of legumes and other forbs...
, national park
National park
A national park is a reserve of natural, semi-natural, or developed land that a sovereign state declares or owns. Although individual nations designate their own national parks differently A national park is a reserve of natural, semi-natural, or developed land that a sovereign state declares or...
s, nature preserves, and other wildlands. These lands are essential for agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
and for protecting the integrity of ecological systems. Natural areas contain many nonnative plant species
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
that occur as self-sustaining populations in the lower 48
Contiguous United States
The contiguous United States are the 48 U.S. states on the continent of North America that are south of Canada and north of Mexico, plus the District of Columbia....
of the United States, including medusahead. As of 2005, medusahead infested approximately 972700 acres (3,936.4 km²) in the 17 western states (from North Dakota
North Dakota
North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....
south to Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
and west to the Pacific coast), and spreads at an average rate of 12% per year. As medusahead spreads, it outcompetes native vegetation, reduces land value, and creates a wildfire
Wildfire
A wildfire is any uncontrolled fire in combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bushfire, forest fire, desert fire, grass fire, hill fire, squirrel fire, vegetation fire, veldfire, and wilkjjofire may be used to describe the same...
hazard.
History and origin
Medusahead was first described in the United States in OregonOregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
in 1903 as Elymus caput-medusae by Thomas Howell. Nevski recommended in 1934 that the Russian types of medusahead should be classified in a separate genus, Taeniatherum. In the 1960s, it was suggested by Jack Major of the University of California
University of California
The University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
that there are three geographic and morphologically
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
distinct taxa: T. caput-medusae, T. asperum, and T. crinitum. After traveling in Russia, Major thought the proper classification for the plant introduced to North America was Taeniatherum asperum. The genus was revised in 1986 by the Danish scientist Signe Frederiksen. He made the previously mentioned distinct taxa into subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
of Taeniatherum caput-medusae.
The subspecies caput-medusae is a native species to Europe, and is mostly restricted to Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
, southern France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, Algeria
Algeria
Algeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...
, and Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
. Subspecies crinitum is found from Greece
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
and the Balkans
Balkans
The Balkans is a geopolitical and cultural region of southeastern Europe...
east into Asia, and the range of subspecies asperum completely overlaps the other two subspecies.
In Asia, medusahead is widespread in Turkmenistan
Turkmenistan
Turkmenistan , formerly also known as Turkmenia is one of the Turkic states in Central Asia. Until 1991, it was a constituent republic of the Soviet Union, the Turkmen Soviet Socialist Republic . Turkmenistan is one of the six independent Turkic states...
, Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...
, Syria
Syria
Syria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....
, and in the northern portion of Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...
, inhabiting low mountains and plateau areas. It is both an agronomic
Agronomy
Agronomy is the science and technology of producing and using plants for food, fuel, feed, fiber, and reclamation. Agronomy encompasses work in the areas of plant genetics, plant physiology, meteorology, and soil science. Agronomy is the application of a combination of sciences like biology,...
and rangeland weed
Weed
A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...
. It prefers soils rich in nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, and is often found on stony or gravelly soils. Carbonized seeds of this weed have been found in early agricultural archaeological site
Archaeological site
An archaeological site is a place in which evidence of past activity is preserved , and which has been, or may be, investigated using the discipline of archaeology and represents a part of the archaeological record.Beyond this, the definition and geographical extent of a 'site' can vary widely,...
s in Iran. Seeds were first found in strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
corresponding to the early days of sheep and goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
husbandry
Animal husbandry
Animal husbandry is the agricultural practice of breeding and raising livestock.- History :Animal husbandry has been practiced for thousands of years, since the first domestication of animals....
.
Life Cycle and Growing Habits
Medusahead is a winter annual, germinating in the fall and undergoing root growth in the winter and early spring. Since its roots develop early and reach deep in the soil, it outcompetesCompetition (biology)
Competition is an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both is required. Competition both within and between species is an important topic in ecology, especially community ecology...
native plants for moisture. It flowers in early spring, and by June or July its seeds, which are covered with tiny barbs, are mature. The barbs help the seeds attach to livestock, humans or vehicles that pass by. As the grass grows it accumulates silica, making it unpalatable to livestock except for early in its life cycle. It creates a dense layer of litter, and because of the silica content, the litter decomposes more slowly than that of other plants. This litter suppresses native plant growth while encouraging the germination
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
of its own seed, and after a few years it creates an enormous load of dry fuel that can lead to devastating wildfires.
Stands of medusahead vary in density from several hundred to 2,000 plants per square foot. This variance is directly related to annual precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
, soil type, and other vegetation in the area. Research has suggested that medusahead is highly adaptable and can produce more seeds at a density of one plant per square foot than 1,000 plants per square foot. Since it matures later than most other annuals, it is easy to identify as it is often bright green when the other annuals are brown. As it matures, it turns shades of purple and eventually tan.
Medusahead seeds disperse
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
relatively short distances and dispersal decreases as distance from the plant increases. Seeds are very well adapted for dispersal by adhesion to moving objects. The relatively long period of medusahead seed dispersal from July to October may be an adaptation to increase the likelihood of adhesion to animals.
Identification
Medusahead ranges in height from 20 to 60 centimeters. It has slender, weak stems that often branch at the base. It has spike inflorescenceInflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
s similar to those of wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
or rye
Rye
Rye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...
. The lemma
Lemma (botany)
Lemma is a phytomorphological term used in botany referring to a part of the spikelet of grasses . It is the lowermost of two chaff-like bracts enclosing the grass floret. It often bears a long bristle called an awn, and may be similar in form to the glumes - chaffy bracts at the base of each...
s have long awns and the glumes have shorter ones, giving the seed head a layered look. As the awns dry, they twist and spread in all directions, similar to the snake-covered head of the mythological Medusa
Medusa
In Greek mythology Medusa , " guardian, protectress") was a Gorgon, a chthonic monster, and a daughter of Phorcys and Ceto. The author Hyginus, interposes a generation and gives Medusa another chthonic pair as parents. Gazing directly upon her would turn onlookers to stone...
. The barbs on the awns help the seed drive into the soil. The grainlike seed may remain viable in the soil for a number of years.
Effects on Wildlife and Grazing
The grazingGrazing
Grazing generally describes a type of feeding, in which a herbivore feeds on plants , and also on other multicellular autotrophs...
capacity of land infested with medusahead can be reduced by up to 80%. Wildlife habitat and biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
also suffer, and the weed can eventually lead to alterations in ecosystem functions. The impact medusahead can have on species relying on sagebrush
Sagebrush
Sagebrush is a common name of a number of shrubby plant species in the genus Artemisia native to western North America;Or, the sagebrush steppe ecoregion, having one or more kinds of sagebrush, bunchgrasses and others;...
is rarely mentioned. It can exacerbate the decline of sage-grouse
Sage-grouse
The sage-grouse are the two species in the bird genus Centrocercus. They are the largest grouse from temperate North America. Adults have a long, pointed tail and legs with feathers to the toes. Like in most Galliformes, there is pronounced sexual dimorphism.-Courtship and Mating:Centrocercus...
(genus Centrocercus) as it replaces plant communities that provide critical habitat for the bird.
Other species, such as mule deer
Mule Deer
The mule deer is a deer indigenous to western North America. The Mule Deer gets its name from its large mule-like ears. There are believed to be several subspecies, including the black-tailed deer...
and chukar partridges
Chukar
The Chukar Partridge or Chukar is a Eurasian upland gamebird in the pheasant family Phasianidae. It has been considered to form a superspecies complex along with the Rock Partridge, Philby's Partridge and Przevalski's Partridge and treated in the past as conspecific particularly with the first...
, tend to avoid areas overrun with medusahead because it is not a good food source. In the case of mule deer, a study in Oregon found that even though extensive stands of medusahead were available, those areas (when compared to other plant communities) were least preferred by feeding mule deer in winter, summer, and fall; and they ranked low in the spring. This decrease in feeding was related back to the dominance of medusahead, which deer do not eat, and the subsequent lack of forb
Forb
A forb is a herbaceous flowering plant that is not a graminoid . The term is used in biology and in vegetation ecology, especially in relation to grasslands and understory.-Etymology:...
s. Chukar partridges will ingest medusahead seeds ( caryopses ) if given no other choice. However, if they are given free access to all the medusahead seeds they will eat, they suffered from a significant loss in body weight. Largely undamaged seeds were found in their droppings, suggesting that the digestibility of medusahead by the birds was low.
Control Methods
No single control method will eradicate medusahead. For best results, it is often necessary use a form of integrated pest managementIntegrated Pest Management
Integrated pest management is an ecological approach to agricultural pest control that integrates pesticides/herbicides into a management system incorporating a range of practices for economic control of a pest...
that combines two or more of the following methods.
Mechanical
Plowing and disking are two methods of mechanical control. Both methods can effectively control medusahead and can reduce infestation by 65% to 95% the next growing season. Eradication of medusahead by mechanical control by itself is nearly impossible, but when followed by chemical control or revegetationRevegetation
Revegetation is the process of replanting and rebuilding the soil of disturbed land. This may be a natural process produced by plant colonization and succession, or an artificial , accelerated process designed to repair damage to a landscape due to wildfire, mining, flood, or other cause...
chances for eradication increase dramatically.
Burning
Fire is often considered a low cost method of improving rangeland condition. It has been given attention in the control of medusahead because many of the areas infested with it are too rocky or steep for other treatments. Control of medusahead with fire had differing results in CaliforniaCalifornia
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. In some areas, more desirable plant communities came back after a fire, while in other areas medusahead continued to dominate after fire. There are a few guidelines that should be followed when burning medusahead. The burn should be conducted when the seed is in the soft dough stage (when the seeds exude a milky substance when squeezed) in the late spring. The initial fire should be one that is slow burning, something that is easily achieved by burning into the wind. This prevents the fire from advancing too rapidly and ensures that the current year's herbage is burned and periods of maximum temperature are long enough to kill medusahead caryopses. Viable medusahead caryopses are found almost entirely in the litter and on the soil surface.
Past studies on the effectiveness of burning may have given researchers false hope. The caryopses have severe temperature dependent afterripening requirements which prevent seeds from germinating at temperatures above 10˚C for about 180 days after maturity. If these conditions are met, many medusahead caryopses from the litter and soil in burned plots were viable. Since the seeds did not germinate during the afterripening period, researchers were misled into believing they were accomplishing more by burning than was actually the case.
Chemical
Chemical controlHerbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
can be effective if used in conjunction with other control methods. Glyphosate (Roundup) applied at 0.375 lbs/acre in the early spring before seeds are produced can provide good results. This timing will also limit the damage to nontarget species that develop later in the growing season. Research suggests that burning before chemical application is more effective than chemicals alone. In the late 1960s, a study was conducted that determined the effectiveness of paraquat
Paraquat
Paraquat is the trade name for N,N′-dimethyl-4,4′-bipyridinium dichloride, one of the most widely used herbicides in the world. Paraquat, a viologen, is quick-acting and non-selective, killing green plant tissue on contact. It is also toxic to human beings and animals...
on medusahead control in different areas of the United States. This study found that paraquat was effective in controlling medusahead in California, but did not suppress the grass in Reno, Nevada
Reno, Nevada
Reno is the county seat of Washoe County, Nevada, United States. The city has a population of about 220,500 and is the most populous Nevada city outside of the Las Vegas metropolitan area...
. This was significant because it determined that there was no effective herbicide for the simultaneous spraying and reseeding of medusahead infestations .
Biological
Medusahead was found to be susceptible to certain root rotRoot rot
Root rot is a condition found in both indoor and outdoor plants, although more common in indoor plants with poor drainage. As the name states, the roots of the plant rot. Usually, this is a result of overwatering. In houseplants, it is a very common problem, and is slightly less common in outdoor...
fungi including crown rot
Phytophthora
Phytophthora is a genus of plant-damaging Oomycetes , whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems. The genus was first described by Heinrich Anton de Bary in 1875...
and take-all
Take-all
Take-all is a plant disease affecting the roots of cereal plants in temperate climates caused by the fungus Gaeumannomyces graminis var. tritici. All varieties of wheat and barley are susceptible...
, but it was not susceptible to barepatch
Rhizoctonia
Rhizoctonia is a genus of anamorphic fungi in the order Cantharellales. Species do not produce spores, but are composed of hyphae and sclerotia and are asexual states of fungi in the genus Thanatephorus. Rhizoctonia species are saprotrophic, but are also facultative plant pathogens, causing...
, browning root rot, and common root rot. The diseases did not reduce the overall weight of the roots, but take-all significantly reduced the overall dry weight of the aboveground shoots. Soil-borne pathogens can have a severe effect on grasses as long as the environmental conditions for the diseases are optimized. Take-all is associated with plants growing in high soil moisture, and like crown rot, it affected medusahead. In contrast, crown rot had the greatest impact on water-stressed plants and therefore may be an effective biological control
Biological pest control
Biological control of pests in agriculture is a method of controlling pests that relies on predation, parasitism, herbivory, or other natural mechanisms...
of grassy weeds in the arid regions of the western U.S. It is also promising because it did not have a significant negative impact on desirable grasses such as western wheatgrass.
Grazing
Grazing alone is not a good method of medusahead control. For best results, grazing is used as part of an integrated program. It is an efficient management tool as long as the timing and duration of grazing are controlled properly. For example, if grazing is carried out in conjunction with revegetation, the desirable grasses must be established before the grazing can take place, otherwise the revegetation will be futile. In areas where desirable grasses have completed their life cycle by the winter or early spring, grazing during this time can help reduce medusahead. It should still be in a vegetative stage and therefore more palatable to livestock. Grazing in the late spring, summer, and fall is not recommended because it will give medusahead a competitive advantage as cattle graze species other than medusahead. If livestock grazing is a method used to control mature stands of medusahead, the livestock must be moved to a holding area for 10 days to two weeks and fed weed-free feed before they are moved to weed-free areas. This will prevent the seeds that pass through the animals from germinating in areas that are free of medusahead.Restoration
Revegetation should be a part of any medusahead management plan. If medusahead is not first controlled, reseeding an infested area will not be successful. The existing medusahead has to be controlled and especially not allowed to produce more seed, and the seed bankSeed bank
Seed bank may refer to:*Seedbank, a repository of preserved seeds*The store of viable plant seed in an ecosystem; for example:** Soil seed bank, the viable seed present in the soil;...
in the soil also has to be reduced. This usually takes two or three years, depending on soil moisture and growing conditions. After this, seedling of desirable species can become established. Combining a tillage
Tillage
Tillage is the agricultural preparation of the soil by mechanical agitation of various types, such as digging, stirring, and overturning. Examples of human-powered tilling methods using hand tools include shovelling, picking, mattock work, hoeing, and raking...
treatment followed by herbicide is most effective in controlling the weed and promoting desirable plant growth. Squirreltail
Elymus elymoides
Elymus elymoides is a species of wild rye known by the common name squirreltail. This grass is native to most of North America west of the Mississippi River. It occurs in a number of ecosystems, from alpine forest to desert sage scrub to valley grassland.-Description:Elymus elymoides is a perennial...
, bluebunch wheatgrass, crested wheatgrass
Agropyron cristatum
Agropyron cristatum is a species in the Poaceae family. This plant is often used as forage and erosion control...
, intermediate wheatgrass
Thinopyrum intermedium
Thinopyrum intermedium is a sod-forming perennial grass. It is part of a group of plants commonly called wheatgrass because of the similarity of their seed heads or 'ears' to common wheat...
, Thurber's needlegrass, needle and thread
Hesperostipa comata
Hesperostipa comata, commonly known as needle-and-thread grass, is a species of grass native to North America, especially the western third. It has a wide distribution spanning from northern Canada to Mexico.-Description:...
, Indian ricegrass, sandberg bluegrass
Poa secunda
Poa secunda is a widespread species of grass native to North America. It is highly resistant to drought conditions, and provides excellent fodder.-External links:**...
, and sheep fescue
Sheep's Fescue
Sheep's Fescue or Sheep Fescue is a species of grass.-General Description:It is a perennial plant sometimes found in acidic ground, for example in the Portlethen Moss, Scotland and mountain pasture, throughout Europe and eastwards across much of Asia; it has also been introduced to North...
are all competitive grasses that work well when renovating an area previously infested with medusahead in the western United States.
Prevention
Since medusahead seeds are often spread by adhering to humans, animals, and vehicles, it is recommended to restrict these kinds of traffic in infestations to prevent the spread of medusahead. Narrow containment zones of around 3 meters would successfully suppress the invasion of medusahead to surrounding areas.Plant communities that have high densities of large perennial bunchgrasses are more resistant to medusahead invasion, so managing rangelands to promote and maintain large perennial bunchgrasses is critical to prevent the spread of medusahead. This will reduce the establishment of new infestations, but successful management will also require searching for and eradicating new infestations. Controlling new infestations is more effective, and oftentimes more feasible, than trying to control large infestations.
Even if attempts to prevent and control new infestations are not entirely successful, these efforts will slow the rate of spread and give researchers and land managers more time to develop better prevention, restoration, and control methods. Also, slowing the rate of invasion helps promote rangeland health and productivity in areas that are most at risk of invasion. Without an active prevention program, this weed will continue to spread and increase its negative ecological and economical impacts. Managing medusahead may seem expensive per acre, but when all the acres that are protected by managing an infestation are considered, the price is very reasonable. And, when taking into account the rising land prices, the cost of medusahead management to the individual livestock producer is rapidly becoming more reasonable compared to purchasing additional acreage to offset production losses from medusahead invasion.
External links
- Species Profile- Medusahead (Taeniatherum caput-medusae), National Invasive Species Information Center, United States National Agricultural LibraryUnited States National Agricultural LibraryThe United States National Agricultural Library is one of the world's largest agricultural research libraries, and serves as a National Library of the United States and as the library of the United States Department of Agriculture...
. Lists general information and resources for Medusahead. - Grass Manual Treatment
- Photo gallery