caput-medusae (L.) Nevski][ELYCM][CalEPPC: A-1][CDFA list: Not Listed] Photographs
SYNONYMS: Elymus caput-medusae L., Hordeum caput-medusae
(L.) Crosson & Durand, Cuviera caput-medusae (L.) Simk.,
Taeniatherum asperum (Simonk.) Nevski, Taeniatherum caput-medusae
(L.) Nevski ssp. asperum (Simk.) Melderis, Taeniatherum crinitum
(Schreb.) Nevski var. caput-medusae (L.) Wipff, and many others.
At publication time the relationships and nomenclature for the taxa in the
genus Taeniatherum remain controversial.
DESCRIPTION: Noxious winter annual
to 0.6 m tall. Medusahead typically invades rangeland communities.
Dense stands often develop, displacing desirable vegetation and wildlife,
and lowering the livestock carrying capacity. Relative to other forage species,
medusahead contains much silica, making it harsh and unpalatable to
livestock except during the early growth stages. The stiff awns and hard florets
can injure eyes and mouths of grazing animals. Seed-eating birds usually avoid
feeding on the seeds. Senesced plants form a dense layer of litter that decomposes
slowly, changing the temperature and moisture dynamics of the soil, greatly
reducing seed germination of other species, and creating more fuel for wildfires.
Medusahead matures 2-4 weeks later in the season than most other
annual grasses. The yellowish-green sheen of dense stands
is highly visible after other annual grasses turn brown. Introduced from Europe.
The western U.S. endemic crown rot fungus (Fusarium culmorum) is a
potential biocontrol agent adapted to dry soils.
SEEDLINGS: Remain attached to the long-awned florets. Vegetative
characteristics are similar to those of mature plants, except blades are ~
0.5 mm wide. Seedlings can survive desiccation of the primary root
and develop adventitious roots when moisture becomes available.
PLANT: Stems slender, +/- ascending. Blades
~1-3 mm wide, flat to +/- in-rolled along the margins, typically 2-4 per stem.
Leaves and sheath glabrous or covered with minute hairs. Sheath open. Ligules
membranous, up to 0.5 mm long, truncate. Collar region usually sparsely long-hairy.
Auricles glabrous, up to ~ 0.5 mm long. The surface of mature foliage often
appears glassy under magnification.
and UNDERGROUND STRUCTURES: Fibrous roots
grow throughout the cool season, deplete upper soil moisture early in the
season, and access deep soil moisture late in the growing season. Seedling
roots grow faster than those of downy brome (Bromus tectorum).
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SPIKELETS/FLORETS: Heads spike-like, 1.5-5 cm long excluding awns, main axis
does not break apart in fruit. Spikelets 2 per node. Florets 2
per spikelet, the upper much reduced and sterile. Fertile lemma narrowly
lanceolate, ~ 5-8 mm long, 3-veined, tapered into a straight to curved
awn ~ 3-7 cm long. Lemma surface covered with minute glassy barbs
and papillae (magnification required). Glumes awn-like, +/- ascending,
1-4 cm long, straight to slightly curved, fused at base. Awns and glumes flattened,
stiff, with minute upward pointing barbs lining margins. Spikelets separate
from the head above glumes. Self-pollinated.
CHARACTERISTICS: Old spikes consisting of
the ascending glumes remain intact for a long period. Some florets can remain
attached to spikes long after plants turn brown.
HABITAT: Disturbed sites, grassland, openings in chaparral, oak woodlands,
agronomic fields. Grows best on clay soils or where deep soil moisture is
available late in the growing season.
DISTRIBUTION: North Coast Ranges, Cascade Range, Klamath Ranges, Sierra
Nevada, Central Valley, South Coast Ranges, northern South Coast (Santa Barbara
Co.), Channel Islands; to Washington, Idaho, Utah. To ~ 2100 m (7000 ft).
PROPAGATION/PHENOLOGY: Reproduces by seed. Seed production is prolific. Seeds
disperse locally with wind and water and to greater distances with soil movement,
human activities, and by clinging to the feet and fur of animals. Newly matured
seeds require a cool after-ripening period of ~ 3-4 months and contain a germination
inhibitor in the awns that must degrade before germination can occur. Germination
is typically rapid and occurs under a broad temperature range (optimal 10-15º
C). Most seeds germinate in fall after the first rain, but some seeds remain
dormant or germinate in winter or spring. Seeds can germinate in dense litter
under low moisture conditions and without directly contacting a moist substrate.
Nitrogen can stimulate some dormant seeds to germinate. Seedlings emerge from
soil depths up to ~ 8 cm (3-4 in).
FAVORING/DISCOURAGING SURVIVAL: Depending
on timing, intensity, and other factors, controlled burns may reduce or enhance
infestations. Slow hot burns initiated when other vegetation has dried and
medusahead seeds have not matured (~ 30 % moisture content), can reduce
infestations significantly. Discing or plowing before seed-set can greatly
SPECIES: Unlike medusahead, similar
appearing Hordeum and Elymus species have 5-veined lemmas
and main flower spike axes that typically break apart in fruit.
In addition, Hordeum species have 3 florets per spikelet, with
the lateral florets much smaller than the central floret.
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Prevention: This invasive
winter annual grass is found throughout rangelands and wildlands of the Western
United States. The serious nature of this undesirable plant is easily recognized
by its ability to invade and outcompete dense stands of downy brome (cheatgrass,
Bromus tectorum) on degraded rangelands. This problem may be compounded in
areas where land managers are aggressively working to control other invasive
plants. Without restoration efforts combined with weed management, ranchers
and land managers alike may unintentionally replace other exotics with the
aggressive medusahead. Controlled grazing may be one of the few ways to prevent
medusahead establishment. This includes areas where cheatgrass is the dominate
forage species for winter and spring grazing. Overgrazing of cheatgrass will
likely shift the balance to favor medusahead, which will result in a downward
spiral of decreased grazing capacity.
Certain soil types have also been shown to favor medusahead establishment.
These include heavy clays or soils with well developed subsurface clay horizons.
Low lying areas that receive additional moisture by overland flow or subsurface
later moisture flow may also favor medusahead.
Mechanical: Where possible,
tillage for seedbed preparation will control existing medusahead plants. Tillage
may also bury seed and break up deep thatch layers. However, the increased
potential for soil erosion, loss of soil moisture, loss of organic matter,
and loss of microbiotic crusts may outweigh the immediate benefits of tillage.
Careful consideration of these factors should be made before utilizing tillage
in rangeland or wildland areas. Mowing is generally nonselective and fails
to remove the meristems where new growth originates. Along roadsides, mowing
is not recommended afer seed set due to the increased potential for seed dispersal.
Biological: Very little
work has focused on utilizing classical biological control for medusahead.
Five soil fungi endemic to the Western United States have been examined. However,
results from that study demonstrated a general lack of host specificity for
medusahead by these fungi. Winter wheat and crested wheatgrass exhibited some
degree of susceptibility to all five fungi. Biological control of medusahead
does not appear to be a potential management option in the near future.
Chemical: Chemical control
options for medusahead are currently very limited. Glyphosate and paraquat
are nonselective herbicides but will only provide variable control of medusahead.
Their use is extremely limited where other sensitive species occur. Atrazine
is a selective herbicide used for annual grass control and has effectively
controlled medusahead and cheatgrass with at 1.12 kg ha-1. However, atrazine
may injure perennial grass seedlings and a fallow period prior to grass seeding
is necessary. This period may be up to twelve months. Atrazine is currently
labeled on a very limited basis for use in rangelands in some states but is
not labeled in California. Limited chemical control options for medusahead
presents a serious potential problem for California rangelands. Current chemical
control strategies in rangelands are dominated by broadleaf herbicides. Controlling
broadleaf weeds such as yellow starthistle may result in a species shift to
medusahead. This has been observed where picloram, a broadleaf herbicide,
was used to control western juniper. Once this shift to medusahead has occurred,
fewer options will be available for restoration of productive rangeland. Thus,
long term sustainable management of rangelands susceptible to medusahead invasion
will require integrated approaches involving revegetation efforts that include
desirable species which occupy critical niches susceptible to weed invasion.
Fire: The use of fire has
given mixed results for medusahead control. Plant community improvements have
been achieved by burning cismontaine areas of California. However, burning
in the intermountain areas has resulted in continued medusahead dominance.
These mixed results are likely due to differences in the soil seedbank, and
plant community recovery time following a burn. An understanding of the natural
fire cycles and plant community response to fire is critical for success in
medusahead management with fire.
Integrated Management: Although
revegetation of medusahead infested areas is critical, successful strategies
have not been abundant. There are certain inherent difficulties associated
with revegetation of infested areas. Medusahead is one of the few grasses
which is adapted for survival on vertisols. These contracting and expanding
clay lattices are somewhat unstable in areas of erratic precipitation, and
perennial grass seedling establishment is extremely difficult. Difficulties
in timing of seedling establishment and seedling predation have also been
encountered. Researchers in Idaho attained successful medusahead control with
atrazine, but failed to get seedling establishment of crested wheatgrass.
Further investigations utilizing soil fumigation revealed an unidentified
biologic factor was involved in preventing seedling establishment. This factor
was not identified, but was speculated to be either an endemic nematode or
The use of squirreltail (Sitanion hysterix) has been successful in areas of
the intermountain region. This perennial grass is one of the only natives
observed to establish in medusahead communities. Bluebunch wheatgrass, (Pseudoroegneria
spicata), previously called Agropyron spicatum, has not been able to establish
in medusahead communities without first removing the medusahead. Greenhouse
and laboratory studies have shown that medusahead can gain a competitive advantage
over bluebunch wheatgrass by rapid germination and early establishment at
low temperatures. Similarly, both medusahead and cheatgrass can germinate
and establish much more rapidly at low temperatures than either crested or
bluebunch wheatgrass, by continuous root elongation over the entire winter.
These studies are a good indication of the competitive ability medusahead
has compared to native perennials. They also suggest that integrated approaches
involving medusahead control may be more successful than revegetation alone.