Garden Vocabulary: Water Grass

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It started as any normal phone call. A homeowner had contacted the Extension office with a question on controlling a grassy weed in her lawn. A weed she knew was ubiquitous in the world of lawn care. However, when she said the name, "water grass", I was dumbfounded. The voice on the other end of the line seemed concerned on my lack of knowledge for 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 typically in Central Illinois a person is using it as a reference 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 take a 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 the germination of seed 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 mid-April and yes it is too late for us in 2016.

Perennial grassy weeds such as nimblewill or quackgrass are some of the hardest to control due to the plant returning every year along with its 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. There is a new herbicide available to homeowners on the market with the active ingredient mesotrione (Tenacity). Mesotrione selectively targets some perennial and annual grassy weeds, but the price tag combined with the amount of product one receives at purchase makes this impractical for homeowners. When battling grassy weeds, it is recommended to consult with a professional lawn care company.

Regardless of the type of 'water grass' in a lawn, there are practices everyone can do to create a more competitive stand of turf.

  • Cool season lawns (Kentucky bluegrass, perennial rye, tall fescue, and fine fescues) should be cut at a 3-inch mowing height.
  • Avoid excessively high amounts of nitrogen fertilizer early in the spring.
  • Minimize compaction by aerating your lawn with a hollow-tine aerator.
  • Keep the lawn as dry as possible. When you water, make sure to water deeply (1-inch) and infrequently (once a week if necessary).

University of Illinois Extension has a great website called LawnTalk with more helpful lawn care information.

Finally, if your yard is overrun with crabgrass, nimblewill, or any of the dozens of possibilities; at least it is green and that's usually good enough for most.