It started as an ordinary phone call. A homeowner contacted the Extension office with a question about controlling a grassy weed in her lawn. A weed she knew was ubiquitous in lawn care. However, when she said the name “water grass,” I was dumbfounded. The voice on the other end of the line seemed concerned about my lack of knowledge of this very common weed. Putting on my best voice of reassurance, I promised to get back with an answer to her question.
Type ‘water grass’ into an internet search, and you will get results ranging from papyrus to ‘how to water grass.’ An email to a colleague gave me what I needed. Water grass is often used to describe any grassy weed in a lawn, but in Central Illinois, it typically refers to crabgrass. A photo from the caller confirmed the weed in question was indeed crabgrass.
Proper identification is key to controlling any weed, especially grassy weeds in a lawn. Let’s look at a few of the main offenders.
Crabgrass is an annual and must come back every year from seed that germinates in the spring. Applying crabgrass preventer (a preemergent herbicide) inhibits seed germination in the spring. Timing is critical, as crabgrass germinates when soil temperatures reach 55 to 60 degrees Fahrenheit for 7 to 10 consecutive days. For West-Central Illinois, that means around early to mid-April.
Perennial grassy weeds such as nimblewill and quackgrass are among the hardest to control because the plants return every year, along with their seeds and spreading habit. The only option when it comes to spraying perennial grassy weeds is a non-selective herbicide that will kill the weed and desirable grass. A new herbicide available to homeowners on the market contains the active ingredient mesotrione (Tenacity). Mesotrione selectively targets some perennial and annual grassy weeds. When battling grassy weeds, it is often recommended to consult with a professional lawn care company.
Regardless of the type of ‘water grass’ in a lawn, there are practices everyone can follow to create a more competitive stand of turf.
- Cool-season lawns such as Kentucky bluegrass, perennial rye, turf-type tall fescue, and fine fescues can be mowed between 2 and 3 inches.
- Avoid excessive amounts of nitrogen fertilizer early in the spring.
- If your lawn is irrigated, water deeply (1 inch) and infrequently (once a week if necessary).
If you are looking for more helpful lawn information, University of Illinois Extension has a great website for lawn care at extension.illinois.edu/lawns.
Finally, if your yard is overrun with crabgrass, nimblewill, or any of the dozens of possible water grasses, at least it is green grass. Plus, you can still mow it like grass, and that’s usually good enough for most.
Good Growing Tip of the Week: Grasses can be warm-season or cool-season, which indicates the time of year when they will typically be green and actively growing. If spraying herbicides to get rid of weed grasses, be sure they are green and actively growing for the herbicide to work effectively.
By Chris Enroth, University of Illinois Extension
