Medusahead
Taeniatherum caput-medusae
Washington State Classification
Class C — Widespread, County-Selected Control
Medusahead causes many detrimental impacts where it invades, including the alteration of an ecosystem to favor its own survival and competing with and reduction of native and forage plants, resulting in the degradation of wildlife habitat.
Quick Reference
Identification
Growth Habit
Medusahead, is a nonnative, winter annual grass that can grow up to 2 feet (60 cm) tall. Plants bloom in the spring after many other nonnative annual grasses. Inflorescences are a dense spike with long awns that can be somewhat spreading and twisting, and are covered in small barbs. The mature spike with its spreading awns is said to roughly resembling medusa’s head, hence its common name.
Leaves
Plants have open leaf sheaths which may be covered with soft short hairs. Leaves are rolled while in bud and later are flat to inrolled. Leaves may be glabrous (smooth and hairless) or covered with short hairs.
Flowers
Inflorescences are erect spikes with long awns, with long awns and sessile spikelets. When mature, they often bend in an almost horizontal position. As the awns dry and turn tan, they may twist and spread, reminiscent of the snake-covered head of Medusa.
Fruit & Seeds
The fruit is a narrowly elliptic caryopsis, 0.16 to 0.22 inches (4 to 5.2 mm) long, with an adaxial groove and pubescent apex. The caryopsis has small barbs of silica.
Impact
Medusahead causes many detrimental impacts where it invades, including the alteration of an ecosystem to favor its own survival and competing with and reduction of native and forage plants, resulting in the degradation of wildlife habitat. Medusahead is a highly competitive species. Its roots grow through the fall, winter and spring, depleting upper soil moisture early in growing season and seedlings have a higher growth rate than native grass seedlings, allowing it to have an advantage acquiring soil resources, even under low nutrient conditions. Its invasion is associated with significant reductions in native vegetation and plant diversity. The silica content of medusahead slows the decomposition of the old plant parts, resulting in the formation of thick, persistent layer of thatch which alters soil temperature and moisture dynamics, limiting the germination of other species. The thatch layer also provides and increases the amount of fine fire fuels, resulting in an increased frequency of fire.
Ecology & Spread
Habitat
It is a well-known rangeland invader and grows in a variety of conditions. Medusahead thrives on soils with a high content of clay and where deep soil moisture is available late growing season. It will also grow on loamy soils and is less of an invader but can be found on well-drained, sandier soils. Please click here to see a county level distribution map for medusahead in Washington.
Spread Mechanisms
Reproduction
Medusahead reproduces by seed. Most seeds appear to be viable for up to 2 years and seed production can be as high as 243 million seeds per acre. The awns attached to seeds are covered in barbs and readily adhere to fur/hair, clothing, and other materials.
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Control Methods
Biological Control
- There are currently no approved biological control agents for medusahead but research is ongoing. Naturally occurring soil bacteria have been found to be suppressive to medusahead and other nonnative annual grasses cheatgrass (Bromus tectorum) and jointed goatgrass (Aegilops cylindrical). Currently research and testing of a native rhizobacterium, Pseudomonas fluorescens strain D7 (Pf D7) is underway as it is showing promise in reducing medusahead infestations.