Medusahead

What is medusahead?

Medusahead is a winter annual grass from the Mediterranean that keeps expanding its range across western rangeland. medusahead identification hinges on two things: its seed head, a short, bristly spike crowned with long, stiff awns that point up and out and give the plant its name, and its timing, since it stays green for weeks after other annual grasses have died.

It is a serious problem because it crowds out nearly everything else. Its high silica content makes it unpalatable to livestock and slow to decay, so dead plants pile up into a dense thatch that changes soil temperature and moisture, keeps other seeds from sprouting and feeds wildfires. Infested range can lose up to 70 percent of its livestock forage, birds and rodents mostly ignore the seed, and the barbed awns injure animals' eyes, noses and mouths.

Medusahead identification: what to look for

The easiest time to spot medusahead is late spring and early summer, when dense stands show up as yellow-green patches after other annual grasses have turned tan. Up close, check whether the awns stay fixed to the seeds and whether the head stays in one piece.

• Seed head: A spike about 1/2 to 2 inches long, not counting the awns. At maturity the central stalk stays intact and often bends almost horizontal, and the bare spike skeleton can stay on the plant after the seeds fall.
• Awns: Stiff, rough and minutely barbed, roughly 1 to 3 inches long and sometimes longer, often twisted, and attached to each seed even after it drops.
• Leaves: Few per stem, very narrow at 1 to 3 mm, rolled, 4 to 12 inches long, smooth or with short soft hairs; under a lens they often look glassy.
• Collar: A tiny ligule and hairless auricles.
• Color and timing: Bright green in early spring. Dense stands keep a yellow-green sheen 2 to 4 weeks after other annual grasses brown, then dry to brown rather than red.
• Thatch: Dead plants leave a thick mat that takes two or more years to break down.
• Seedlings: Young seedlings often still have the long-awned floret attached at the base.

Where it grows in the United States

Medusahead has been recorded in Arizona, California, Idaho, Nevada, Oregon, Utah and Washington, with outlying sites in Nebraska and a few northeastern states, and it continues to spread across the West. South Dakota State University Extension warns that its arrival on South Dakota rangeland is a matter of when, not if. In California it is found mainly in the central and northern parts of the state, up to about 6,900 feet.

It favors places with at least about 9 inches of rain a year, so it is uncommon in the low deserts, and it does best on clay soils or sites that hold moisture deep into late spring. Grasslands, rangeland, oak woodland and chaparral openings are prime targets, especially once they have been disturbed, and it only rarely moves into farm fields.

Medusahead look-alikes

A few plants get mixed up with it:

• Bottlebrush squirreltail: Its flowering head has a similar bristly shape, but the awns detach from the seed at maturity, while medusahead's stay attached.
• Foxtail barley (Hordeum jubatum): Another bristly head of similar shape, but again the awns separate from the seed as it ripens. Medusahead's awns remain fixed to the seed.
• Downy brome (Bromus tectorum): Often grows in the same places. Downy brome turns red as it matures, while medusahead dries brown, and medusahead stays green several weeks longer.

How to get rid of medusahead

Pulling, digging and mowing: Mowing early in spring is likely to fail and can hurt other plants, but mowing at the boot to early flowering stage can suppress medusahead; mowing after seed set only spreads it. Raking, tilling or burning off the thatch layer weakens its hold and helps other plants establish. Tillage before seed set kills plants, buries seed and breaks up thatch, but on rangeland the erosion, moisture loss and damage to soil crusts can outweigh the benefit. Whatever you do, act before the seed matures, and expect to repeat the work for several years.

Cultural control matters most, because the right conditions keep it from coming back.

• Graze hard in spring while it is still palatable, ideally at the boot to head-emergence stage, then move animals off before seeds mature so they don't carry seed around.
• Burn in late spring when plants are starting to head but before seed drops. In warm-winter areas such as California's Central Valley foothills, two years of burning can nearly eliminate it, but burns usually fail at high, cold sites.
• Follow a spring burn with a fall preemergence treatment to go after the seed left in the soil.
• Help desirable perennial grasses recover so they can hold the ground once medusahead is knocked back.
• Use certified weed-free hay and seed, and clean vehicles and equipment after driving through infested areas.

Herbicides: Herbicides work best as one part of a multi-year plan. University research summarized by UC weed scientists points to fall treatments as the backbone: imazapic in fall in warm-winter areas or just after snowmelt in cold climates (it is not registered in California), rimsulfuron from fall preemergence to early spring, and aminopyralid, a broadleaf-selective product that gave strong medusahead control in fall trials in California's Central Valley. South Dakota State University Extension reports University of Wyoming success with indaziflam, with native perennial grasses recovering. Glyphosate can be used in spring after all seedlings are up and before heading. A thick thatch layer reduces how well soil-applied products work, so burning or removing it first helps, and multiple treatments are often needed to shift the plant community. Use only products labeled for your site and follow the label exactly; it is the law. If you hire someone to spray, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Keeping it from coming back

Medusahead seed doesn't last long, mostly about two to three years, so stopping seed production for a few seasons pays off quickly. The hard part is catching new infestations early. Learn its late-green look, record and report new patches to your county weed board, and treat small outlying patches before they become solid stands.

Its awned seeds travel on animals, clothing, vehicles and hay, so buy certified weed-free hay and clean seed, and wash vehicles and equipment after driving through infested ground. Keeping perennial grasses healthy leaves it less room to move in.

Questions we get about medusahead

Similar weeds

Foxtail BarleyHordeum jubatumDowny Brome (Cheatgrass)Bromus tectorumCogongrassImperata cylindrica