Yellow nutsedge (a.k.a. watergrass) is going strong all over Kansas City lawns right now due to the wet spring and hot temperatures. This weed is the “Weed from Hell” for homeowners and lawncare companies. Nutsedge is so tough and prolific that even a product that kills everything it touches, like Round Up, won’t control it.
If you notice tall grasses that stick up above your lawn and are lighter in color than your grass, you’ve got nutsedge. Though it looks like grass, nutsedge (also called nutgrass or swampgrass) is neither a grass nor a broadleaf weed. It is a variety of weed called sedges. Nutsedge can reproduce by seeds but it also produces rhizomes (stems that grow underground and sprout new plants) and tubers (which store food and also produce new shoots.) These tubers are also called “nuts” or “nutlets” and that is where the plant gets its name. This system of underground rhizomes and nutlets make nutsedge hard to kill.
Unfortunately, once it is established, it is not easily controlled. According to the latest study from the University of California, Davis, a nutlet can reproduce seven to eight times after each new plant is removed by pulling or spraying before it reaches the six-leaf stage. After a plant reaches the six-leaf stage it is mature enough to start producing more nutlets, which means more plants next year.
With this new information the latest protocol to control nutsedge is to spray with products like Sedgehammer or Dissmiss and/or pull the plants before they reach maturity. This is quite the opposite from previous recommendations in which studies found that if you wait until the plant is mature you get better kill and it won’t send up so many new young plants. Now we understand why we kept having more problems each year, we were trying the win the battle by controlling the top but were losing the war by letting it produce more nutlets for next year.
So, the long and the short of it is – getting yellow nutsedge under control will require a team effort. We will spray every time we treat and you will have to pull every time you spot one in the lawn. If we beat it back 7-8 times we will make headway on reducing the population next year. If you want to read the entire study it can be found here http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7432.html