Dallisgrass vs Crabgrass: One Comes Back Every Year

Two grassy weeds, nearly identical at a glance, requiring opposite strategies. Mistaking one for the other is why some people spray the same patch for three summers and never win: they are applying an annual-weed playbook to a perennial plant.

The Four Checks That Settle It

Work down this list. Any single one is usually decisive.

1. Growth habit — the fastest tell

Crabgrass sprawls. Blades radiate outward from one central point in a low fan or star, pressed close to the ground, and stems often root where they contact soil.

Dallisgrass stands up. It forms a tight, upright clump — a distinct tuft that sits noticeably above the mow line rather than spreading sideways.

2. The base of the plant

This is the definitive check. Part the blades and look at where they meet the soil.

Crabgrass has a soft, fibrous crown you can pull apart with your fingers.

Dallisgrass has a thick, woody, almost knotted crown — a perennial structure that stores energy through winter, often with short rhizomes radiating from it. It resists pulling, and if you do pull it, it tends to break rather than lift.

3. Does it return to the same footprint?

Crabgrass cannot. Every plant dies at frost and next year’s plants grow from scattered seed, so the pattern moves around the lawn.

Dallisgrass does. The same clump regrows from the same crown, in the same place, for years. This history question alone identifies it in most yards.

4. Seedheads

Crabgrass produces several finger-like spikes radiating from one point at the top of a stem.

Dallisgrass sends up taller seed stalks bearing sparse paired branches, often with small dark spots visible on the seed, and it produces them persistently through the season even in mown turf.

For sorting any lawn weed into its family first, start with the weed identification guide. And if you want to check your plant against a photograph rather than a description, Texas A&M AgriLife’s Weeds of Texas Turf gallery is a photo reference for turf weeds — identification only, which is the right tool for this step.

Hawaii Lawn Threat Matrix

What to scout for on Bermuda lawns in USDA zones 9a–13a.

High-Risk Weeds

• Goosegrass
• Crabgrass
• Kyllinga and nutsedge in wet ground
• Oxalis
• Spurges in hot compacted strips
• Dollarweed on over-watered turf
• Kikuyugrass, which behaves as a weed in a lawn of anything else

High-Risk Diseases

• Large patch and brown patch (Rhizoctonia) on zoysia and St. Augustine, running whenever warm humid conditions persist — which on the windward side is most of the year
• Dollar spot
• Pythium diseases where heat, humidity and standing water meet
• Plant-parasitic nematodes, which on sandy and volcanic soils are a genuine cause of thin, unresponsive turf here rather than an exotic diagnosis — the CTAHR diagnostic centre tests for them
• Take-all root rot on St. Augustine
• Nutrient-deficiency symptoms that mimic disease, because leached Oxisols hold so little

Common Pests

• Lawn armyworm — present on every major island, and Hawaii's species is apparently not found anywhere else in the United States, so mainland guidance about it is not about this insect
• Grass webworm and the other turf caterpillars, which CTAHR treats as the state's leading turf insect group
• Little fire ant, a relatively recent arrival whose sting raises welts that burn for days; it travels in potted plants, mulch, firewood and soil, and control means baiting every four to six weeks until surveys come back clean
• Plant-parasitic nematodes
• Chinch bugs on St. Augustine
• Billbugs and white grubs

Regional relevance: dallisgrass is not among Hawaii's top documented weeds, so crabgrass is the more probable answer — but check the crown anyway, because the treatment paths diverge completely. Both compete hardest where Bermuda has thinned.

Why the Difference Changes Everything

The annual-versus-perennial distinction determines which tools can work at all.

The practical consequence: a pre-emergent program that eliminates crabgrass from a lawn in two or three seasons will leave a dallisgrass clump completely untouched. If you have been “winning against everything except that one patch,” that patch is the perennial.

Why these two do well in Hawaii specifically: your soils are Volcanic soils throughout, of two very different kinds: Andisols formed in ash on the younger slopes, and drainage reads: Fast on the ash Andisols, which have low bulk density and take water readily, and fast again on young volcanic ground that has barely weathered; slow only in the deep clay pockets, so on most Hawaii lawns the problem is nutrients leaving rather than water sitting. Dallisgrass in particular tolerates the wet, compacted conditions that thin turf roots, so it colonizes low spots and traffic lanes long before it appears in healthy areas — which is why core aeration belongs in your weed plan, not just your maintenance plan.

Treating Dallisgrass, Honestly

This is where most lawn content oversells, so here is the straight version.

The product that used to be the answer is gone. Maryland Extension states it plainly: “Herbicides that contain MSMA and DSMA, which were classically used to control Dallisgrass, are no longer labeled to be used on home turf.” Remaining registrations are limited to professional settings such as golf courses and sod production, so any advice that still recommends MSMA for your yard is out of date.

What is realistically available to a homeowner:

1. Repeat quinclorac applications. Products containing quinclorac suppress dallisgrass with mixed and often modest results. Expect several applications across a season, spaced per the label, and expect regrowth from the crown.

2. Excavation for isolated clumps. For a handful of plants this is the most reliable route. Dig several inches wider and deeper than the clump to remove the entire crown and surrounding rhizomes, then refill and replant.

3. Spot-kill and renovate. For heavier infestations: treat the clumps with a non-selective herbicide, confirm a complete kill, observe the label’s replant interval, then re-establish turf.

   Be clear about where that last one comes from, because we would rather you knew. NC State’s dallisgrass publication does not publish it — their page says only that “selective control measures are usually difficult” and points at prevention: “maintaining a dense, healthy turf year round by proper mowing and fertilization helps prevent encroachment and weed establishment.” Spot-killing is what is left once the selective options are ruled out, and it is the same route quackgrass takes for the same reason — including the wiped rather than sprayed application that keeps the surrounding lawn alive. It is a reasonable inference, not a recommendation we can hand you someone else’s name for.

Nothing here is a one-application fix for established dallisgrass. Anyone promising that is selling you the pre-ban product or selling you disappointment.

The Frost Test in Hawaii

Hawaii hands you a free identification every year. First frost arrives around no date at all — frost reaches only the high summits of Mauna Kea, Mauna Loa and Haleakala, never the elevations where lawns are kept — and frost kills crabgrass outright while dallisgrass shrugs it off. Walk the lawn two weeks after that date: any coarse clump still green is dallisgrass, no stem-rolling required.

The ground tilts the odds too. Dallisgrass thrives in heavy, moist soils, and Hawaii's profile — Volcanic soils throughout, of two very different kinds: Andisols formed in ash on the younger slopes (Hilo, the state soil, is one and covers about 21,000 acres of prime ground) and highly weathered Oxisols on the old windward slopes, fast drainage — is exactly what it likes, so expect the perennial half of this fight to be the longer one here. On Bermuda, that also decides which herbicides the label allows.

Rainfall settles which of the two dominates your lawn. Hawaii rainfall reads: The steepest rainfall gradient in the United States, from leeward slopes under 20 inches a year to windward mountain slopes measured in hundreds. Two lawns twenty miles apart can need irrigation and drainage respectively. Humidity: Humid year-round on the windward sides, drier on the leeward, with trade winds rather than seasons doing the work — and no winter dormancy at all, so growth and mowing never stop. Dallisgrass needs sustained moisture to hold its crown through a season, so that steady supply lets it establish well beyond the wet corners — expect it across the lawn, not only in low spots. Soil pH also decides your herbicide options, and here it is usually acidic.

Mark those survivors while they are easy to see, because your next moves are seasonal. Fall work here: Nothing changes seasonally, so use this period for the jobs a mainland calendar would put in autumn: aeration, dethatching, renovation. The spring barrier window that stops the crabgrass half of the problem opens There is no single spring flush to time against — warm-season weeds germinate through much of the year, so pre-emergent here is a repeated programme on label intervals rather than a February or March decision. Last frost, for planning repairs, lands around no date at all — Hawaii has no frost season, which is why a mainland seasonal calendar has to be rebuilt here rather than shifted a few weeks.

Compaction is the shared precondition for both weeds, and relieving it is a separate job with its own timing — see how to aerate your lawn.

Keeping Both Out

Both weeds exploit the same opening: thin turf with light reaching bare soil.

• Never let either set seed. A single season of seed production reloads the seed bank you have been trying to empty.
• Mow at the top of your grass type’s range. On Bermuda, follow the species range rather than a generic number.
• Water deeply and infrequently so turf roots outcompete shallow-rooted invaders.
• Feed on your regional schedule. In Hawaii: Rate follows species: hybrid bermudagrass has the highest requirement, zoysia, St. Augustine and seashore paspalum are intermediate, and centipede needs the least. Because growth never stops and the soils leach, the pattern is lighter and more frequent rather than two or three big applications — and seashore paspalum wants nitrate-N rather than ammonium-N during establishment.
• Aerate compacted areas annually — both species tolerate compaction better than turf does.
• Scout the same spots each summer. Dallisgrass returns to its footprint, so a photo record of last year’s clumps tells you exactly where to look.

And here is the summer practice your own state's calendar calls for, which is the one most people skip: Watch the leeward and windward halves of your own property differently; the rainfall gradient can operate across a single lot. Getting that right does more against both weeds than an extra herbicide application, because it removes the opening they need.

One tool belongs on that list with an asterisk, and the asterisk is this whole article. A pre-emergent is the strongest thing you can do about crabgrass, because crabgrass is an annual that has to start from seed every year — kill the germination and the plant never exists. It does essentially nothing about established dallisgrass, which is a perennial returning from its own crown and rhizomes rather than from the seed bank. Same granule, same morning, two completely different outcomes.

The window in Hawaii is There is no single spring flush to time against — warm-season weeds germinate through much of the year, so pre-emergent here is a repeated programme on label intervals rather than a February or March decision, and that is a soil-temperature condition rather than a date. Dallisgrass is not on Hawaii's own high-risk weed list; the listed pressure is Goosegrass and Crabgrass. So if you have clumps that survived a pre-emergent, identify before assuming — the four checks above are faster than another application.

Next steps in this cluster: the full annual sequence in our crabgrass guide, and the sedge that fools everyone in how to get rid of nutsedge.

If the perennial has taken enough of the lawn, selective control stops being the answer: Penn State treats the presence of perennial grass weeds as grounds for a kill-off regardless of how much good grass is left. See how to kill a lawn before reseeding.