Couch grass, or as it is commonly called Bermuda grass, is a warm season turf that can be an invasive pest at times. Gardeners often struggle keeping this grass out of their lawns; couch grass' ability to thrive in poor soils and survive droughts makes it a difficult grassy weed to control.
Couch grass characteristically has hairy leaf sheaves that can reach heights of 6 inches long and blades can grow to 7 inches tall. Its extensive rhizomes spread vigorously across lawns. Older roots can be brown or yellow, while new roots are white. Because this grass grows in the spring, gardeners can expect that its seeds start germinating right after the last frost. Without a preemergent herbicide application, couch grass can start to take over lawns.
Preemergent herbicide prevents couch grass seed from germinating. The weed seeds need consistent soil temperatures between 20 and 24C / 68 and 75F in order to grow. Couch grass also needs full sunlight or it will only germinate and grow in patches under shade. Spraying preemergent herbicide is a safe method to prevent from hurting existing grass. However, it must be applied before the weed seed starts growing. Early spring is the optimal time for applying preemergent herbicide.
Postemergent herbicide must be applied when the weed is growing. There are two types of herbicide generally used: non-selective and grass selective herbicide. Non-selective herbicide will kill any type of vegetation that it comes in contact with in the yard. In fact, spraying it near seedlings, ornamental plants and grass can result in dead debris within a few days. For gardeners hoping to control their couch grass before sewing grass seed, non-selective herbicide works for clearing out the couch grass in the yard prior to seeding.
Selective herbicide is chemically formulated to only kill couch grass. According to the University of California Cooperative Extension, the optimal time to spray couch grass with selective herbicide is when it has reached the height of 6 inches. A second application must be sprayed before the regrowth reaches an additional 6 inches. Generally, gardeners should spray their grass with selective herbicide in the spring and summer months. The more leaf surface the couch grass has the higher success rate the selective herbicide will be on ridding the grassy weed.
Other herbicides act to suppress or harm couch grass leaves and stems, but do not eradicate the grassy weed. Combined with postemergent herbicide used on grass blades shorter than 6 inches, they can control the weed from invading the lawn. However, it is important to not spray this type of herbicide near other vegetation, because it will harm grass and ornamental plants.