Because they often blend in with your lawn, weeds that look like grass can establish themselves before you realize they’re there. At that point, they’ve been taking nutrients from your lawn for weeks, gathering the strength to fight off your control efforts. Knowing how to identify common grassy weeds lets you get the jump on them before they make themselves too comfortable.
Annual Bluegrass (Poa annua)
Annual bluegrass is a lighter, brighter green than its relative Kentucky bluegrass and produces a long ligule, or membrane, that holds the base of the leaf to the stem. When viewed from the side, the leaf tips curve up like the bow of a ship. It prefers cool, moist conditions and is likely to turn brown when summer temperatures rise.
Foramsulfuron can get rid of existing annual bluegrass, and it’s safe for some turfgrasses. Several pre-emergent herbicides, including bensulide, dithiopyr, and oryzalin, can be applied in the fall to stop annual bluegrass from coming up in spring.
Crabgrass (Digitaria sanguinalis)
This common lawn weed is named for its distinctive horizontally spreading crab-shaped growth habit. Full grown crabgrass leaves are bright apple green with a central fold and noticeably wider than the leaves of most lawn grasses. It’s a warm-season annual that thrives in hot weather.
To spot treat a small crabgrass patch, thoroughly douse it with vinegar of 5 percent acidity or higher and repeat the process for several days or until the crabgrass dies.
Herbicides containing quinclorac control crabgrass without harming most turfgrasses. Some pre-emergents such as dithiopyr, prodiamine, and pendimethalin are safe to use on healthy, well established lawns. Ultimately, a thick, healthy lawn is the best defense against this weed.
Quackgrass (Elymus repens)
Also known as common crouch, quackgrass is a cool-season perennial most easily recognized by its auricles, the finger-like leaves that grasp the stems and project outward from them. The grass spreads aggressively through rhizomes and forms coarse-textured, ashy blue-green patches.
The safest way to get rid of small patches of quackgrass is to dig it up by the roots or solarize it by covering it with black plastic, such as a black bucket, for at least four weeks during the height of summer. Spot treatment with a non-selective herbicide is also an option. Keep in mind that non-selective herbicides can also kill any lawn grass they touch, so careful application is essential.
Creeping bentgrass (Agrostis palustris)
This cool-season perennial grows as a dense, fine-textured mat and spreads through stolons, forming gray-green patches that stand out as light spots in most turfgrasses. It starts to look puffy when it grows past 1 inch, but it tolerates short mowing well, making it a popular choice for golf courses. While it flourishes in cool, wet spring weather, it turns brown when temperatures heat up. Mesotrione is one of the most effective herbicides for controlling creeping bentgrass.
Nutsedge (Cyperus sp.)
Two species of this perennial weed show up in lawns: yellow nutsedge (Cyperus esculentus) and purple nutsedge (Cyperus rotundus). They favor wet areas and produce long, narrow leaves and brush-like flowers in either yellow in mid-summer or dark reddish-purple in late summer.
Dig up a clump, and among its roots you’ll find the “nutlets” that give this sedge its name. Post-emergent herbicides containing sulfosulfuron work well for controlling nutsedge, but killing off the nutlets is essential. Avoid overwatering your lawn.
Carpetgrass (Axonopus sp.)
Boggy, shady areas with acidic soils are the preferred home of both broadleaf carpetgrass (Axonopus compressus), sometimes called blanketgrass, and narrowleaf carpetgrass (Axonopus affinis). These grasses form a dense, coarse, medium-green mat that can grow up to 12 inches high. Both warm-season perennials, they turn green late in spring, send up tall, crabgrass-like seedheads in summer, then turn brown as soon as temperatures drop again.
Dousing this grass with a solution of 1/4 cup salt in 1 gallon water is often enough to kill it, but if it doesn’t, allowing the soil to dry out or applying lime to lower the soil pH might. Oryzalin is effective as a pre-emergent herbicide.
Broom sedge (Andropogon virginicus)
A warm-season perennial, this grass grows upright in narrow bunches, particularly in sunny areas of low soil fertility and low soil pH levels such as abandoned lots and near railroad tracks. It’s medium green in summer, then turns a coppery orange and stiffens in fall.
Herbicides aren’t much help here. Contrary to its name, this plant is a grass, not a true sedge, so many treatments that control it also harm turfgrass. Spot treating with vinegar or any non-selective herbicide is your best bet for small areas. In large areas, proper fertilization and liming as needed gets rid of broom sedge over several years.
Johnsongrass (Sorghum halepense)
Young johnsongrass resembles corn seedlings and quickly matures to a height of up to 7 feet. Its 1/2- to 1-inch-wide leaves are marked by a white vein running down the center. From May to the first frost, this warm-season perennial produces purplish flowerhead tufts that can grow up to 1 foot long.
The simplest way to get rid of this grass is by dousing the seedlings in vinegar or digging them up and disposing of them. For larger patches, the herbicide sulfosulfuron is one of the most effective choices, and it won’t harm most turfgrasses. If you’re willing to re-seed or re-sod in spring, tilling the soil in autumn gets rid of johnsongrass by bringing the rhizomes to soil surface, where the winter cold will kill them.
Goosegrass (Eleusine indica)
This annual silvery-green grass is most easily identified by its flowerhead comprised of two to 10 finger-like strands that spread out like a goose’s foot. It grows in a spreading formation like crabgrass, but can also grow straight up to 16 inches.
Goosegrass thrives in compacted, poorly drained soil, so aerating your lawn helps discourage this weed, as can applying corn gluten meal to your lawn in spring. For chemical treatment, a combination of benefin and trifluralin works as a pre-emergent, while mesotrione is an effective post-emergent. Dithiopyr can work as both.
Foxtail (Setaria sp.)
These warm-season annual grasses are best known for the long, bottle-brush flower spikes they produce in late summer. They grow in nearly any soil conditions, forming clumps between four to 40 inches across.
The three species you might find are yellow foxtail (Setaria pumila), the smallest species with yellowish-orange flower spikes, green foxtail (Setaria viridis), a larger species with greenish-beige flower spikes, and giant foxtail (Setaria faberi), which can reach up to 7 feet and produces drooping flower spikes.
Spot-treating with vinegar works for small clumps, but for large areas, use a pre-emergent herbicide containing acetochlor or a non-selective herbicide. Alternatively, repeatedly till the weeds under in summer.
Weeds that look like grass are easy to mistake for one another, so accurate identification is an essential first step toward controlling them. Once you know what you’re dealing with, you can choose a natural control method or a chemical herbicide that will kill the grassy weeds without harming your lawn grass species.