Weed management is among the most important duties of homeowners who want to preserve the aesthetic quality of their lawn grass. Weed species move into lawns, gardens and other growth areas and compete with cultivated plants for moisture and nutrients, thereby threatening the life of the plants you grow. Recognizing weed species is the first step to designing an effective control strategy, and often the best way of identifying weed species is by observing their physical characteristics.
There are many different species of weeds that may be attacking your lawn, but the only one known to resemble corn is crabgrass, one of the most common invasive grasses. Crabgrass looks almost exactly like a corn stalk in its youngest growth stages. A crabgrass seedling that is just beginning to sprout from soil will have 1/4-inch leaves and can easily be mistaken for a young corn plant.
Crabgrass is sometimes difficult to characterize by its physical characteristics because it can adapt to many different growing conditions. Fully grown crabgrass will usually be around 6 inches tall, though the large crabgrass species can grow up to 2 feet tall. Because crabgrass is an invasive, competitive species, it can often also be identified by the damage it causes in the plant species around it. Brown patches will often break out around the crabgrass, and in temperatures below 40 degrees Fahrenheit, the crabgrass itself will brown out.
Hand pulling is a natural control method, but crabgrass tends to be highly successful wherever it occurs, so manual pulling can quickly become time-inefficient. Since crabgrass competes with other grass species, keeping your lawn healthy and vigorous can choke the crabgrass out of existence. Select a species of grass that is well suited to your climate and soil conditions, and overseed when starting a new lawn to keep lawn grass thick. Vigor is ensured through irrigation, mulching, fertilization, proper mowing and other cultural management practices.
A serious crabgrass invasion may require the use of an herbicide for complete control. Pre-emergent herbicides (those that are applied before crabgrass shows up) recommended for crabgrass control typically contain bensulide, dithiopyr, oryzalin, oxadiazon, pendimethalin, prodiamine and trifluralin. Post-emergent "rescue treatment" herbicides applied after crabgrass appears usually have dithiopyr, fluazifop, quinclorac and sethoxydim as their active herbicide ingredients.
- University of Nebraska-Lincoln Extension; Crabgrass Management; Don Janssen
- University of California Agriculture and Natural Resources Statewide IPM Program: Crabgrass
- University of Florida IFAS Extension; Crabgrass Management Is Difficult!; Doug Caldwell
- The Garden Counselor: What Does Crabgrass Look Like?