Cheatgrass in hay fields is a timing problem disguised as a grass problem. The weed, also called downy brome, sprouts after fall rains, sits through winter as a small green seedling and heads out in your first cutting, where its awned seedheads lower the hay’s value and can hurt livestock mouths. By the time many growers notice it in May, the best window to act has already closed. October and November are when it pays to look.
Quick answer: Cheatgrass (Bromus tectorum) is a winter annual: it germinates after fall rains, overwinters and sets seed in late spring or early summer. Confirm the identification first, because foxtail barley and other bromes look similar. In established alfalfa, Extension guides point to fall treatment after the crop goes dormant and before the ground freezes, with a short late-winter window before green-up. Grass hay has far fewer labeled options. Keep stands thick, cut before seed matures and follow the current label.
This guide is for alfalfa and grass-hay growers, including those who sell to horse owners, and for anyone who found drooping, purple-tinged seedheads in last spring’s bales. It is not a spray recommendation. Herbicide registrations differ by state and change over time, so check the current label and your local Extension office before you treat anything. XES manufactures bale net wrap; we compared archived farmer discussions with university Extension guides, research and product labels.
Why cheatgrass shows up in hay fields
Cheatgrass does not run on the same clock as the perennial grasses you seed for hay. Cornell University’s downy brome weed profile reports that most seedlings emerge in the fall after significant rains, that plants survive 10 °F with little damage, and that roots keep growing in soil as cold as 37 °F. Iowa State University lists flowering in April and May, and Cornell says seed matures about four weeks after flowering. Under Montana conditions, Montana State University Extension says plants set seed and die between mid-July and early August.
"Downey Brome germinates and emerges in fall, over winters, and then becomes trouble in spring. Gotta do something to break up it's growth cycle."
— Rodney R, HayTalk thread 12995
That head start is why thin stands fill with it. Cornell notes that uniform stands prevent establishment and warns against grazing that leaves gaps larger than 24 inches. The University of Nebraska–Lincoln’s downy brome guide (G422) calls it especially troublesome in alfalfa and says it invades overgrazed pastures. Anything that opens the canopy in late summer or fall — winter injury, a thin new seeding, close grazing, wheel traffic — gives fall-germinating seed a place to start.
"Cheat grass shows up as it is early and can smother out other grasses that I've sown."
— Missouri hay hauler, HayTalk thread 103792
The good news is that the seed bank is short-lived. Cornell reports maximum seed longevity in undisturbed soil of 2 to 5 years, with the great majority of seed germinating the first fall after it is shed. Most plants produce 10 to 80 seeds in typical conditions and more than 500 in favorable ones. Stopping seed production for two or three seasons can drain a field, which is why every section below comes back to the same goal: no new seed.
Identify it before you spray
Downy brome has a long list of common names. UNL’s list includes cheatgrass, downy chess, cheat and even wild oats, and several look-alikes share fields with it. One alfalfa grower asked HayTalk how to stop “cheatgrass” that had just headed out in a thin new stand, collected advice, and then reported back:
"I contacted our local extension guy and he as identified the grass as foxtail barley."
— mulberrygrovefamilyfarm, HayTalk thread 14758
That difference matters. Colorado State University Extension describes foxtail barley as a short-lived perennial bunchgrass, so a fall treatment aimed at a winter annual will not fix it. Use the table with a hand lens, then confirm with your county Extension office or a diagnostic lab before you buy herbicide.
| Grass | Life cycle | Leaves | Seedhead |
|---|---|---|---|
| Cheatgrass (downy brome, Bromus tectorum) | Winter annual | Coated with short, soft, downy hairs; no auricles | Drooping, one-sided panicle; awns 0.4–0.7 inch; often purple-tinged, tan when dry |
| Japanese brome (field brome, Bromus arvensis) | Annual | Easily mistaken for cheatgrass; check the chaff instead | Similar panicle; outer chaff of each spikelet has three ridges instead of one |
| Cheat (chess, Bromus secalinus) | Annual | Largely hairless | Awns no longer than 0.2 inch |
| Foxtail barley (Hordeum jubatum) | Short-lived perennial bunchgrass | Perennial clumps that return each year | Bristly seedhead with sharply barbed awns; favors wet or alkaline spots |
Sources: Cornell University weed profile; Iowa State University downy brome entry; Montana State University Extension; Colorado State University Extension.
If you are establishing a perennial brome, get the seedlings identified before you act. A young smooth brome seeding is the crop you want to protect; our smooth brome hay guide covers that stand.
What cheatgrass does to hay
Cheatgrass is not worthless forage. UNL describes it as palatable before the seedheads emerge. The trouble is timing: it heads out early, so by first cutting its seedheads are often drying and its awns hardening. Iowa State University says the awns irritate the mouths of grazing animals, damage it calls “bromitis,” and UNL notes that mature downy brome can cause infection in the eyes or mouth.
UNL Extension educator Todd Whitney wrote in April 2026 that winter annual weeds such as downy brome can lower first-cutting yield, quality and palatability, and can lengthen dry-down and harvest time. Growers put it more bluntly:
"I have zero fields anymore where I can grow timothy without getting some if not half of the hay ruined by downy brome."
— Rodney R, HayTalk thread 103792
A grower who took over an orchardgrass field full of downy brome reported that the bales basically fell apart
(HayTalk thread 12995). For horse-hay sellers the risk is reputational as much as nutritional; our guide to foxtail in hay explains how awned seedheads injure horses’ mouths and why buyers reject them. UNL also lists hay among the ways downy brome seed spreads, so a contaminated lot can seed a buyer’s field.
The cheatgrass control calendar
Because the plant runs on a fall-to-spring clock, the calendar does more work than any single product. Use this as a planning frame; exact dates move with your rainfall and latitude.
| Period | What the cheatgrass is doing | What fits |
|---|---|---|
| Late summer to early fall, before fall rains | Seed waiting on the soil surface | Preemergence products registered for your crop. For trifluralin in alfalfa, the PNW Weed Management Handbook says to apply right after a cutting between August 1 and October 1 when downy brome is a target. Repair thin spots. |
| Fall, after emergence and alfalfa dormancy | Small seedlings, easy to miss from the road | The main window in established alfalfa. UNL’s forage specialist says to spray before soils freeze. |
| Late winter to early spring, before green-up | Seedlings resume growth | A short dormant-season window; UNL warns there are often only a few days when alfalfa is still dormant, weeds are growing and the weather allows spraying. |
| Mid to late spring | Heading and flowering | Too late for most herbicides. Cut between flowering and the dough stage, or put heavy patches up as baleage. |
| Summer | Seed shed; plants dying | Map the patches and plan fall control and stand repair. |
Many growers first meet the problem in that fourth row, which is why forum advice in May often starts the same way:
"Well you may be a month late to catch any of those winter brome grasses."
— hay wilson in TX, HayTalk thread 14758
Options in established alfalfa
Established alfalfa has the most tools, and most of them are dormant-season products. UNL forage specialist Bruce Anderson’s fall guidance names metribuzin, Sinbar and Velpar as probably the three best choices, adding that all three do an excellent job on downy brome. The table summarizes what the Pacific Northwest Weed Management Handbook lists for winter annual grasses in established stands. It is a starting point for a conversation with your dealer, not a substitute for the label you buy.
| Active ingredient (example product) | Timing | How it works on cheatgrass | Key limits listed |
|---|---|---|---|
| Metribuzin (TriCor, Dimetric) | Fall after alfalfa is dormant, before spring growth | Soil residual; one of UNL’s three fall picks | No grazing or harvest within 28 days; stands established 1 year or more; not on sand |
| Hexazinone (Velpar DF) | Fall after dormancy, before spring growth; best before or soon after weeds emerge | Soil residual; one of UNL’s three fall picks | No grazing or harvest within 30 days; stand at least one growing season old; persists in soil up to 24 months |
| Terbacil (Sinbar WDG) | Dormant alfalfa after frost but before January 1 | Soil residual; one of UNL’s three fall picks | Stand 1 year or more; no replanting any crop within 2 years |
| Pendimethalin (Prowl H2O) | Fall after the last cutting, winter dormancy, spring or between cuttings | Preemergence only: controls annual grasses as they germinate | No hay harvest within 14 days |
| Trifluralin (Treflan) | Before weeds emerge; for downy brome, right after a cutting between Aug. 1 and Oct. 1 | Preemergence only; will not control established weeds | No hay or grazing within 21 days |
| Paraquat (Gramoxone SL 3.0) | After the last fall cutting when dormant, before spring growth | Contact burndown of emerged seedlings; often paired with a residual | Restricted-use pesticide; no cutting within 30 days; no grazing before first cutting |
Three cautions from the same sources. The PNW handbook calls diuron “not very effective on downy brome.” UNL’s Whitney writes that Poast “will control most growing weedy grasses, but not downy brome,” and that glyphosate products must be used with Roundup-tolerant alfalfa varieties. And a preemergence product applied after cheatgrass is already up will not control it, which may explain some of the failures growers describe.
Rotate modes of action, too. Washington State University’s herbicide resistance screening found downy brome samples in 2024 and 2025 resistant to several Group 2 herbicides, the Group 1 product Assure and glyphosate. Those samples came from eastern Washington wheat systems, not hay fields, but the lesson travels: a product that suddenly stops working deserves a resistance test, not a heavier rate.
Options in grass hay
Grass hay is where growers run out of answers. Chemistry that removes an annual grass can also thin timothy, fescue or orchardgrass, and some products sold for “pasture and rangeland” are written around grazing land rather than intensively managed hay meadows. Two labels show why the fine print decides.
Plateau (imazapic). The Plateau label (EPA Reg. No. 241-365) covers pastures, rangeland, CRP land and noncropland areas, including noncropland areas that may be grazed or cut for hay, and lists downy brome among the weeds it controls. It also says “DO NOT cut treated area for hay within seven days after treatment,” and it includes a table of how established grasses tolerate fall applications. AgTalk users disagree sharply about it: one warned it will kill most of your cold season grasses
, while another replied that thousands and thousands of acres of pasture have been sprayed for cheatgrass using Plateau
(AgTalk thread 1213254). That disagreement is the reason to check your species against the label’s table instead of a neighbor’s result.
Rejuvra (indaziflam). The Rejuvra label (EPA Reg. No. 101563-208) describes a preemergence herbicide for rangeland, CRP lands and natural areas, “including any of these sites that are grazed or cut for grass hay.” The same label says it “is not intended for use on areas grown for grass seed production or on areas intensively managed for grass hay production,” naming timothy, fescues, bluegrasses and perennial ryegrass, and says “DO NOT export hay from treated areas.” A HayTalk member who used it on a mixed stand in 2026 reported:
"I used Rejuvra with excellent results. It is very pricy but the only thing that was effective while not killing the perennials in the stand."
— KNPV-PSD, HayTalk thread 103792
Asked whether it hurt timothy, the same grower answered that it will likely kill a fair amount of it
, depending on how shallow-rooted the stand is. Timothy grown for hay sales is exactly the case the label carves out. For grass hay, ask your Extension office which products your state’s labels allow on your hay species, and expect cultural control to carry more of the load.
Tools that work without a sprayer
- Thicken the stand. Gaps are the entry point. Our guide to thickening a thin hay field covers late-summer seeding and frost seeding, and whether to take a last cutting covers fall management that protects a stand going into winter.
-
Cut before seed matures. Cornell reports that mowing between flowering and the dough stage greatly reduces seed production, but plants cut earlier can resprout and seed can still mature on clippings cut at the dough stage or later. A HayTalk grower summed up the bind:
If you cut it too soon it will grow back. Cut to late and it will reseed itself and no one will want that hay.
(HayTalk thread 44138) - Graze it early, twice. Montana State says grazing takes at least two defoliations each spring, for at least two consecutive years, to keep cheatgrass from producing seed, and it should happen before plants turn purplish-red.
- Turn a heavily infested first cutting into baleage. In a Weed Science study, Blackshaw and Rode (1991) found downy brome seed nonviable after 8 weeks of ensiling or 24 hours of rumen digestion. Our guide to wrapping wet hay covers how to make baleage.
- Don’t import seed. UNL lists hay among the ways downy brome spreads. Feed purchased hay of unknown origin in one area and check that spot the following fall.
Feeding or selling hay with cheatgrass
Sort infested bales into their own lot and label them. Leafy hay cut before heading is the most usable; hay with mature, awned heads is a poor fit for any animal and the wrong product for horse buyers. Tell buyers what is in the lot and price it accordingly; our guide to selling hay covers lot descriptions. If you sell into certified weed-free hay markets, check your state program’s rules before you list the lot.
Keep the lot from seeding your own fields. Feed it in one place, preferably where you can watch for seedlings next fall, or ensile it. For the wider weed picture, including grazing and haying restrictions on pasture herbicides, start with our weed control guide for hay fields.
Frequently asked questions
When should you spray cheatgrass in a hay field?
In established alfalfa, the main window is fall after the alfalfa goes dormant and before the soil freezes, with a short late-winter window before green-up. Preemergence products go on before the seed germinates. Once cheatgrass is heading in spring, cut it before seed matures and plan fall control.
Will Prowl H2O kill cheatgrass?
Not once it is up. Pendimethalin is a preemergence herbicide; the Pacific Northwest Weed Management Handbook says it controls annual grasses as they germinate. It is listed for established alfalfa with a 14-day harvest interval. Emerged cheatgrass needs a different labeled product or a cut before seed set.
Is hay with cheatgrass safe to feed?
Leafy cheatgrass cut before heading is palatable forage, but mature seedheads carry sharp awns that can injure mouths and eyes. Keep awned hay away from horses, feed it carefully and tell buyers. Ensiling infested forage made downy brome seed nonviable in a Weed Science study, which also limits spread.
How do you tell cheatgrass from foxtail barley?
Cheatgrass is a winter annual with soft, hairy leaves and a drooping, one-sided panicle of awned spikelets that is often purple-tinged and turns tan. Foxtail barley is a short-lived perennial bunchgrass with a bristly, sharply barbed seedhead, often in wet or alkaline spots. Have Extension confirm before treating.
Does mowing get rid of cheatgrass?
Mowing between flowering and the dough stage greatly reduces seed production, but it will not eliminate cheatgrass on its own. Earlier cuts can regrow and set seed, and later cuts can leave seed to mature on the clippings. Combine timely cutting with a thicker stand and fall control.
The bottom line on cheatgrass in hay fields
Cheatgrass in hay fields is won or lost in the fall. Identify it, thicken the stand, use the dormant-season window your label allows, and never let it set seed in your first cutting. Clean first-cutting hay is easier to bale tight and easier to sell, and when it is ready, XES bale net wrap helps those bales hold their shape from field to feeder.
Research note: We read all five archived HayTalk discussions with cheatgrass or downy brome in the title (23 captured posts; one turned out to be foxtail barley) and cheatgrass comments in 49 other HayTalk and AgTalk threads, then checked the linked Extension guides, research and product labels on October 6, 2026. Label details here are summaries; the label on the product you buy is the legal authority. Post counts include questions and replies; they are not counts of farms or field trials.
Featured photograph: Dach-Trespe (Bromus tectorum) in Hockenheim, AnRo0002, dedicated to the public domain under CC0 1.0, via Wikimedia Commons. Cheatgrass seedheads photographed in Germany in April 2016; not an XES field. Image unchanged apart from display resizing.
