Cyperus rotundas better known as nutgrass is a bother for avid gardeners all over the globe. In the USA, you might hear of purple nutgrass or purple nutsedge, or in South Africa, Wintjiekweed or red grass, Teki in Indonesia or Motha in India. As you can see, us Queenslanders are not the only ones dealing with this little green shoot and is actually commonly referred to as the “world’s worst weed!”
There is no doubting this little weed is a pest for the gardener and landscaper but it doesn’t end there! Nutgrass has been known to shoot through thick asphalt as well as pierce through pool liners in various parts of the world; there just seems to be no stopping this little guy!
Identifying the Problem
The reddish-purple colour of the flower spikelets is one of the best ways of identifying nutgrass from other weeds and grasses. But that’s only if you allow it to grow to a size where it produces its spikelets. Quite often nutgrass is found sprouting out of a recently laid lawn and in those situations it can be identified by its rapid growth and stronger, stiffer upright blades. The nutgrass will generally grow faster than the lawn and be clearly taller.
I’ve never had it before!
Nutgrass is a thrifty and persistent little weed. It has been shown that nuts can remain dormant or inactive in soil for up to 10 years. There have even been reports of nuts up to 30cm below the surface in heavy clay soils shooting after being disturbed by vehicle movement. The weight of a vehicle shifts and cracks the earth allowing water and oxygen deeper into the soil.
Nutgrass growth is severely restricted by shade. Most other weeds and many larger crop or landscape plants can eventually dominate nutgrass, but rarely will they completely suppress it. Nutgrass will almost always persist if not adequately controlled due to its complicated interconnected network of underground rhizomes (stems). Nutgrass grows most rapidly in full sunlight when adequate nutrients are available. It becomes more serious when allowed to grow without competition from other plants and this can occur when annual weeds are removed manually or by herbicide, crops are harvested or the topsoil is cultivated or disturbed for new plantings.
As stated above, nutgrass only competes well in perfect growing conditions. It is for this reason that infestations are often noticed for the first time when we spend a little time in our gardens. Fluffing up, cultivating or improving the soil, importing new rich fertile soil, fertilising, weeding, removing old plants and heavy watering are all activities that can disturb nuts and encourage them to shoot.
Generally speaking, nutgrass nuts would very rarely be transported within commercially produced planting media. This is due to the fact that most soil blends are finely screened as well as aged and heat treated in large wind rows prior to arriving at the point of sale. This process would also expose the nut to optimal growing conditions many times over before finally landing “on the shelf”.
Control and Management
The best approach for avoiding a nutgrass problem is to prevent establishment of the weed in the first place. Once established, nutgrass plants are difficult to control. You can prevent establishment through the use of manual and chemical control methods. Remove small plants before they develop tubers, eliminate the wet conditions that favours growth, use fabric mulch in garden beds (geo fabric), drying and shading. In cases where the above methods are just not possible, like in a new lawn or heavily planted garden bed, control can also be achieved using properly timed applications of specialty herbicides.
Glyphosate (Group M Herbicide) is the common ingredient in many store-bought herbicides and is often marketed as Zero or Roundup. Although touted as being a kill all weed killer, some studies have shown Glyphosate to yield mixed results when used on nutgrass infestations. However, according to a report from the Cotton Catchment Communities carried out by the NSW DPI, Glyphosate can translocate within the sprayed nutgrass plant and attached tubers.
This translocation means that glyphosate can kill the nutgrass plant it is sprayed on as well as attached tubers and nuts through underground rhizomes. The best results have been seen on fully established nuts already displaying their coloured spikelets typically over 4 weeks old.
This is obviously great news, but remember, glyphosate is not selective! Everything it directly touches will also be poisoned. For situations where overspray can cause collateral damage, like in the home lawn a group B Herbicide with the active constituent Halosulfuron-Methyl or more commonly known as Sempra should be used. Sempra inhibits acetolactate synthase, a key enzyme in the plant’s metabolic pathway. This inhibition stops plant growth and plant death occurs 14 to 21 days after initial application. Sempra does not persist for long in the soil, with a half-life of up to 34 days. Unlike glyphosate, it is reported that Halosulfuron-Methyl does not translocate throughout the attached tubers, so multiple applications may be required if the infestation is particularly advanced. In many cases, a one-off treatment is sufficient.
Crack it Before it Cracks You
So there you have it, nutgrass is a tough little nut to crack and a headache to many around the world. However, a nutgrass infestation is not the end of your garden, nor should it cause you endless sleepless nights and weekends battling the weeds in the garden. They key is to stay ahead of your nemesis and not to let it take over an area with the intention to spray it later. Best practice is as soon as you see any sign of a shooting nut attack it with a dose of Sempra (remember, Sempra is a SELECTIVE poison used to treat specifically nutgrass and as a bonus, Mullumbimby couch). As long as you treat new infestation early, Sempra should be your weapon of choice!
Remember, seek quality when shopping for your garden products! Here at Centenary Landscaping Supplies we guarantee our soils don’t come with nutgrass and if for some reason you have a nutgrass issue after using our products, let us know! We will do everything we can to investigate the ‘root’ source and help you treat the issue if it was in fact imported with the top soil.