Cyperus rotundas better known as nutgrass is a bother for avid gardeners all over the globe. In the USA, you might hear of purple nut grass or purple nut sedge, 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 “worlds 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 the one of the best ways of identifying nutgrass from other weeds and grasses. But that’s generally if you allow it to grow to a size where it produces its spikelets. Quite often nutgrass is found sprouting out of your recently laid lawn and in those situations it can be generally 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 Nutgrass before!
Nutgrass is a thrifty and persistent little weed. It has been shown that nuts can remain dormant or inactive in undisturbed 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 above causing the soil to shift and crack 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 they rarely can completely suppress it and it 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 really only survives or competes well in perfect growing conditions, it is for this reason that quite often nutgrass infestations are 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 or 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 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. Not to mention, these soils would generally 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 as 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, using 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.
Glysophate (Group M Herbicide) is the common ingredient in many store bought herbicides and falls under many names including Zero and Roundup and can be purchased ready-to-use or as a concentrate. Although touted as being a kill all weed killer, some studies have shown glysophate 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 glysophate can translocate within the sprayed nutgrass plant and attached tubers and plants. This translocation means that glyphosate can kill the nutgrass plants it is sprayed on, but can also kill attached tubers and nutgrass plants that were not sprayed directly. 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, glysophate is not selective! So 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 application. Sempra does not persist for long in the soil, with a half-life of up to 34 days. But unlike glysophate, 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 country and 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, one of the best ways to ensure nutgrass isn’t transported within your bulk landscape supplies is to always seek quality when shopping for your garden products!