Medusahead is a winter annual native to the Mediterranean region of Eurasia. It is one of the primary range weeds in the western United States. It is a serious threat to rangelands with sparse native plant communities and more complex communities degraded to a low seral state. Medusahead is an aggressive competitor with other plants including other annuals in California's foothill rangelands. A low-value forage species for livestock and wildlife, it has been estimated that the carrying capacity of rangeland for domestic livestock has been reduced by 75 percent after medusahead invasion.
Medusahead was introduced into the United States from the Mediterranean region of Eurasia, where it consists of three geographically and morphologically distinct taxa. It was originally mistakenly classified as Elymus caput-medusae which originates from Siberia. Another species, Taeniatherum crinitum, grows in North Africa and in the southern Balkans through the Middle East to Soviet Central Asia. The third, Taeniatherum asperum, our western American weed, originally was found from Hungary through Ukraine to Tadzhikistan.
The late l800s is believed to be the approximate time of introduction of medusahead into the United States. The plant 0probably was brought to North America through dispersal of seed by imported animals. The first known specimen submitted to the University of California herbarium was collected near Roseburg, Oregon in 1887. In 1901, it was recorded from Steptoe Butte in eastern Washington, and in 1908, near Los Gatos, California.
It has spread from its original infestation near Roseburg, Oregon to the Palouse region of Washington and Idaho, to southern Idaho and the northern half of California where it has been an invader since the early 1900s.
Medusahead probably has not reached its ecological limit. The plant successfully competes and overlaps both in area and in local habitat ecology with two other exotic, annual range invaders soft chess brome (Bromus mollis) in California and southern Oregon and cheatgrass (Bromus tectorum). If the requirements of medusahead completely overlap those of cheatgrass it could spread widely in the Great Basin.
Environmental Factors
Medusahead grows over a wide range of climatic conditions. Annual precipitation on medusahead sites throughout the four Western States ranges from 10 inches to 40 inches. Medusahead grows where precipitation occurs during fall, winter, and spring. Distribution of precipitation is more significant than total precipitation in meeting the species moisture requirements.
Medusahead grows where extended periods of great cold are lacking. Moreover, some of these climates are extremely hot. Medusahead requires a cold treatment and possibly light stimulus after germination for seed formation to occur. In one study, successful seed formation occurred after exposing seedlings to nightly temperatures of 37F for 14 days in the field. The seedlings matured in the greenhouse.
Soil conditions suitable for growth of medusahead are somewhat variable. Favorable environmental factors related to medusahead distribution are soils with a high clay content and well-developed profiles, and areas receiving run-off water from adjacent sites. Less susceptible to invasion are well-drained soils and those developed from rocks weathered to coarse-textured sands showing poorly developed profiles. Late maturity of the species in relation to other annual grasses and its subsequent requirements for high water-holding capacity clay soils are the accepted explanation for medusahead abundance on clay soils.
Growth Characteristics
Medusahead is able to compete effectively with desirable forage species because of the following growth characteristics: (1) rapid fall germination and root growth throughout the winter, (2) prolific seed production, and (3) accumulation of litter that decomposes slowly.
Medusahead seedling roots begin post- germination growth in the fall and grow all winter, thus effectively reducing available soil moisture to competitors. Medusahead also matures later than neighboring competitors because its root system remains functional for a longer period of time.
Medusahead is a highly prolific seed producer with germination rates of 98 percent. In dense stands, plant numbers ranged from 1,500 to 2,000 per square foot on valley bottom soils, and 500 plants per square foot on scablands. Average number of seeds per head for these two sites were 9 and 6, respectively.
Once medusahead becomes established it grows in dense stands, forming a mat of stems 2 to 5 inches thick. The high silica content of medusahead may be the reason it is slow to decompose. Evidence indicates that the dense litter cover is important in the competitive relationship with other annuals, because most neighboring competitors fail to grow under the accumulated thatch. Medusahead's litter also is an extreme fire hazard in the summer and ties up nutrients otherwise available for plant growth. However, it has been reported that the accumulation of slowly decomposing litter may safeguard soil from wind and water erosion.
Nutritional Characteristics
Moisture content, crude protein, crude fiber, and lignin contents of medusahead compare to other annual range species at similar growth stages (Table 1). However, ash content of medusahead was found to be greater than that of cheatgrass. The ash of medusahead contained approximately 72 to 89 percent silica and amounted to more than 10 percent of the dry weight of plant. The high silica content of medusahead is thought to be the basis for its harshness. The long barbed awns and sharp, hard seeds of the mature plant injure eyes and mouths of livestock.
Although numerous reports have indicated medusahead is unpalatable, other investigators have found heavy livestock grazing on immature plants in early spring. Range fertilization, especially with N, offers a possible way to improve the palatability of medusahead and to encourage its early use by grazing animals. An in vitro nutritive evaluation revealed that immature medusahead had a higher cellulose digestion value than a mixture of desirable annual range forage species.
Control - Reducing Medusahead Density
Fire: A slow hot fire after medusahead seeds have ripened but before they drop will reduce medusahead up to 90 percent the following year. Grazing should be deferred to build up fuel. A properly timed burn for medusahead is when the other vegetation has dried and dropped its seeds.
Chemical: Herbicides applied in March and April will reduce medusahead. Check with your Ag. Commissioner to determine which herbicides are registered for this use.
Grazing Management: Intensive grazing during the growing season will reduce medusahead in about two years. Time controlled grazing reduced medusahead from 45 percent of the cover to less than 10 percent in southern Tehama County. Stock densities of six 500-700 lb. stocker calves per acre were used on this Tehama County ranch.
Mechanical: Disking and plowing before seed set can reduce medusahead by 90 percent or more.
Control - Increasing Density of Competition
Fertilization: Nitrogen fertilization can reduce medusahead by increasing competition from other grasses and forbs, by increasing palatability, and by depleting soil moisture.
Annual legumes: Before reducing medusahead some thought must be given to what will replace it. Annual legume (subterranean and rose clover and lana vetch) seedings following one of the above control methods will replace medusahead with a very desirable plant. Left unseeded Mother Nature will be free to choose the replacement plant. If you are lucky she will choose filaree. But she could just as well choose a less desirable plant.
Perennial grasses: Seeding of perennial grasses such as perlagrass or Berber orchardgrass would be an alternative if grazing management is changed to time controlled grazing. Perennial grasses are unlikely to survive continuous grazing. Success with perennial grass seedings is variable and highly dependent on rainfall patterns.
References
Hilken, Thomas O., and Richard F. Miller. 1980. Medusahead (Taeniatherum asperum Nevski): A review and annotated bibliography. Station Bull. 644, Agric. Exper. Sta., Oregon State Univ., Corvallis.
George, Melvin R., Ronald S. Knight, Peter B. Sands and Montague W. Demment. 1989. Intensive grazing management on annual range. Calif. Agric. 43(5):16-19.
