Eradicating Nutgrass from fallows
Nutgrass is a perennial weed that plagues farmers. Ryan Osborne, Graduate Agronomist from Elders Bowen (QLD) gives some tips for the removal of Nutgrass in the lead up to planting.
Nutgrass (Cyperus rotundus) is a perennial sedge that grows 20 to 50 cm tall with dark green leaves up to 6 mm in width. It reproduces via laterally spread rhizomes that form large colonies. It can be prolific due to the ability to remain dormant for up to seven years in good conditions and germinate from depths of 40 cm with limited moisture.
Nutgrass is difficult to kill due to large energy stores (starch) underground in tubers. The growing point of Nutgrass remains in basal bulbs below the surface allowing it to grow back after being cut at the surface via a slasher or mulcher.
How to identify Nutgrass
Nutgrass (Cyperus rotundus) is commonly confused with many other species from the Cyperus family including C. esculentus, C. eragrostic, C. brevifolius, C.difformis and C. congestus.
There are some simple characteristics to look for when identifying Nutgrass:
- Leaf colour: the leaves on C.rotundus are darker green compared to brighter greens seen on other species such as yellow nutgrass (C. esculentus).
- Flower colour: The colours on Cyperus rotundus flowers are reddish/purplish brown.
- Flower form: Cyperus rotundus have unique umbrella shaped flowers compared to close relatives that have dense bottle brush shaped flowers.
C. rotundus underground structure showing rapid spread through tubers( black), rhizomes (blue) and basal bulbs (red).
Did you know?
- Nutgrass is not a grass! The Cyperus species is part of the sedge family.
- Cyperus rotundus was named after the shape of its tubers. Rotundus meaning round.
- Studies have found Cyperus rotundus can populate up to 5000 shoots per m2.
The control of Nutgrass during fallow periods can be a difficult task due to built-up tubers in the soil. However here are some things you can do to assist with control:
Rapid growing cover crops in fallow periods, such as sorghum, cowpeas and soybeans will provide ground cover and ground shading, allowing no light for Nutgrass to germinate.
Double knock sprays
Spray early before the plant has built up large carbohydrate reserves. Follow this with a second spray once the plant has recovered enough to trans locate a second spray (1.9L/ha+ 1.9L/ha Roundup ultramaxx label rate.).The initial application causes stress, forcing the plant to use stored energy to recover. This leaves no reserved energy for the plant to recover from subsequent herbicide applications
*Note: Halosulfuron–methyl group B herbicides perform well on C.rotundus, however long residual times do not suit horticultural situations.
Tip: Adding one per cent Ammonium sulphate to glyphosate spray mixes improves efficacy by acting as a water conditioner and adjuvant.
Tillage passes spreads rhizomes and tubers throughout the paddock.
Tractor and implement hygiene
Good hygiene will stop the movement of Nutgrass rhizomes and tubers between paddocks.
Intergrated weed management (IWM) strategies
Take a holistic weed management approach. Appling multiple tools to manage the spread of Nutgrass over an extended period. IWM creates cropping system sustainability by lowering the risk of herbicide resistance, diminishing seed bank numbers and lowering future weed management costs.
Note: When using chemicals, it is advised all label rates are followed.
Elders sells a range of crop protection products. View our range.
For more information contact your nearest Elders branch.