Weeds - Grass Weeds Information and Photo Gallery

Onion Couch


Onion couch (Arrhenatherum tuberosum) is a loosely tufted perennial grass that grows to a height of between 50 and 150 cm. It has yellowish coloured roots. The leaves are up to green with sheaths are rounded at the back. Individual blades are flat, finely pointed 10 to 40 cm long and 4 to 10 cm wide. Its a very coarse grass. Basal internodes of the culms are bulbous or pear shaped hence its name.

Occurrence and spread

Onion couch is widespread throughout the British Isles and is commonly found in rough grassland, close to hedgerows and on waste ground. It is a troublesome weed on arable land, competing directly with winter wheat. It can increase teh risk of lodging and hinders harvesting.  Yield losses can reach 0.5 tonnes/ha  or more if infestations are heavy. It spreads by detaching its bulbous bases, each bulbil can produce a new plant.

Control and management

Onion couch is a difficult weed to control on cultivated fields. Best control will be achieved by herbicides such as glyphosate or imazamethabenz-methyl applied when the grass is actively growing. There have been reports that glyphosate is not always very effective at killing the detached bulbils. Seek advice from your BASIS qualified adviser.


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