Dallisgrass: identify it, treat it, keep it out

Did the clump come back from the exact same spot this spring? Crabgrass is a summer annual that dies at frost and restarts from seed, so a clump that greens up in place year after year is a perennial. Dallisgrass is the most common perennial suspect in a southern lawn.

Next, check the leaf. Peel one blade back from the stem and look at the ligule, the small flap where the blade meets the stem. Texas A&M describes dallisgrass as having a long membranous ligule and a prominent midrib, two features that separate it from crabgrass. Still unsure? Dig one clump. UC IPM notes that dallisgrass rhizomes have short internodes that look like concentric rings, which crabgrass does not have.

Seed heads settle it from late May through October, per Texas A&M. Dallisgrass raises a tall stalk with several drooping branches spaced up the stem, while crabgrass splays its fingers from one point. If you still have both suspects, the dallisgrass vs crabgrass comparison walks through the differences side by side.

The answer is underground. Texas A&M explains that dallisgrass grows short rhizomes that widen the plant and store carbohydrates, and those reserves make it hard to control even with systemic herbicides. Pre-emergent herbicides will not control existing perennial plants, per the same publication, so a crabgrass preventer only blocks new seedlings.

The product that used to handle it is gone from home lawns. Texas A&M notes that as of November 2015, EPA restrictions forbid applying MSMA on residential, commercial, or athletic field properties, and University of Maryland Extension confirms that MSMA and DSMA products are no longer labeled for home turf. Most of what remains is labeled only for suppression, which Texas A&M defines as significant activity without commercially acceptable control.

Where is the clump growing? UC IPM says dallisgrass thrives in drainage ditches, low spots, and heavily irrigated turf, and UMD notes it adapts to poor drainage. If your clumps cluster in the wettest part of the yard, correcting the drainage or watering is part of the fix.

Timing matters as much as the product. Texas A&M recommends at least three applications: the first in fall, no earlier than September, once the average 24-hour air temperature stays below 72°F for three days in a row; a second 4 to 6 weeks later when the clumps regrow; and a third at spring regrowth in mid to late April. Fall applications while the plant is still actively growing beat late spring or summer ones.

• Bermudagrass or zoysiagrass: Texas A&M reports that three sequential applications of Tribute Total (thiencarbazone, foramsulfuron, and halosulfuron) gave 60 to 80 percent control for 9 months, and that Revolver (foramsulfuron) is labeled for suppression. Both are labeled for warm-season turf only.
• St. Augustinegrass or centipedegrass: Celsius applied alone as a spot treatment is the only selective option Texas A&M lists, and it suppresses rather than controls. Clemson HGIC also lists dallisgrass among the weeds Celsius controls in warm-season lawns.
• Tall fescue: the warm-season products above will severely injure it. Texas A&M found a single fall application of fluazifop gave greater than 80 percent control for 12 months, and notes that Fusilade II is not for home lawns while Ornamec may be applied to them.

Do the sources agree on fescue? Not entirely. UC IPM names Fusilade II as the cool-season option, while Texas A&M restricts that brand to registered applicators in residential areas. The label on the product in your hand settles it, so check that it lists home lawns and your grass.

For a handful of clumps, the direct route is mechanical. Texas A&M advises using a shovel to remove the entire clump and its rhizomes, backfilling with topsoil, and seeding or plugging the hole. A careful glyphosate spot treatment is the other option, but it kills any turf it touches, so plan to reseed those spots too.