Nutgrass, a noxious weed, is part of the sedge family. You will usually notice its 3 shiny and light green blades rapidly shooting up above your lawn. In most cases it rears its ugly head after you have disturbed the soil; be it by putting in topsoil, renovating your lawn or topdressing your yard.
It is a persistent weed that has been known to lay dormant for up to 10 years! Nutgrass grows quite rapidly when conditions are favourable and can be a little tricky to control due to its complicated interconnected network of underground rhizomes. You will likely see nutgrass growing in full sun where you have recently fertilised and moist soil.
Your best chance of avoiding a serious nutgrass infestation is to take action as soon as you notice it appear. Once established, nutgrass can be difficult to control as you need to remove the plant in its entirety to stop it reappearing.
You can manually remove the small plants before they develop tubers or use a herbicide to control its spread. Should you choose a herbicide you can either use Roundup, which is non-selective which means it will kill anything it comes in contact with or a selective herbicide that tackles Sedge species specifically such as Sempra or Sedgehammer.
Although Roundup is not selective and will kill everything it touches, it has had mixed reviews on its effectiveness in killing nutgrass. According to a report carried out by the NSW DPI, Glyphosate (the key ingredient in Roundup) can translocate within the sprayed nutgrass which means it will kill off any tubers attached to the parent plant. The best results were seen on fully established plants approximately 4 weeks old.
Alternatively, Sempra or Sedgehammer can be used. Both of these products inhibit a key enzyme in the plant’s metabolic pathway which in turn stops the plant growth and plant death will occur between 14 to 21 days after the initial application. Sempra does not persist for long in the soil and doesn’t translocate the way Roundup does so multiple applications may be necessary.