Weed Of The Month: Crabgrass
 | Author:
Allison Kosto, MSU Broadwater County Extension Agent
MSU Broadwater County Extension Agent |
Weed Of the Month: Crabgrass Allison Kosto, MSU Broadwater County Extension Agent Contrary to popular belief, crabgrass is not common in Montana. It is often confused with quackgrass. Due to changing climates crabgrass is being reported more frequently than several decades ago. However, it does not cause the headaches that we hear from states further south. It is important to recognize though since its management vastly differs from quackgrass.
Description & Habitat Native to Europe and Eurasia, crabgrass was introduced to the United States in 1849 by the US Patent Office as a potential forage crop. It is now naturalized throughout the continent. It is commonly found in lawns, landscaped areas, gardens and cropland.
Crabgrass and quackgrass both stand out in lawns and are commonly confused. They both have thick coarse leaves compared to common lawn grasses such as Kentucky bluegrass. However, there are some key differences. Crabgrass often has prostrate growth which means it grows along the ground rather than straight into the air. Young plants are a yellowish-green and often easily distinguishable from dark green turfgrasses. As it matures, older leaves turn a dark red color.
Crabgrass is a warm-season annual grass (life cycle of one year) while quackgrass is a cool-season perennial (life cycle of more than two years). Crabgrass is more common in the semi-tropical and temperate areas of the county. In Montana, lawns are dominated by cool-season grasses. Cool-season grasses grow vigorously in the spring and fall when the weather is cooler and usually out compete warm season grasses such as Crabgrass which prefer to grow in the heat of the summer.
Management. Like any pest, correct identification is the first step to managing the issue. If you need help identifying grasses, stop by the Extension Office with a specimen or picture. As already emphasized in this article, this plant is often misidentified so take the time to get the correct identification. There are many products on the market to prevent crabgrass such as “Crabgrass Preventer” or “Crab-Ex”, which are typically pre-emergent herbicides often mixed with fertilizer. These products are not marketed correctly for Montana and are not worth the investment in our state.
The best way to control or prevent crabgrass is to establish a healthy lawn. Established lawns should be watered less frequently and more deeply and need 1 to 3 inches of water a week. Ideally, you should fertilize based on a soil analysis. Montana lawns typically need more nitrogen than phosphorus or potassium. Choose a high nitrogen fertilizer (i.e. 25-5-5). Fertilize around Memorial Day, Labor Day and Columbus Day. Fall fertilizing is more important than spring. Fertilize about 1 lb. of available nitrogen per 1000 square feet per application or based on your soil analysis. Kentucky bluegrass mixes can be mowed to about 2 inches but never more than 1/3 of the blades at a time.
If you do have crabgrass, it can likely be controlled by hand pulling or digging with the primary goal to prevent it from going to seed. Mowing is typically not successful because plants can still go to seed beneath the mower blade level. Spot spraying is also an option.
If you need help with plant identification, pest management options or lawn care, contact the MSU Extension Office in Broadwater County at 406-266-9242 or allison.kosto@montana.edu.
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PhotoCredit: Allison Kosto
Image 1 Caption: Crabgrass
