Importance
False oat-grass is very common in grassland and in hedgerows throughout the British Isles. The onion couch variant is a more localised problem, generally in loams of more open texture. Once present it is very difficult to totally eradicate as each root nodule can develop into a new plant and they are very resistant to dry conditions.
Description
Very tall perennial 60-150 cm. Swollen bulbous nodules at the stem-base indicate the onion couch variety of false oat-grass. Panicle is like miniature wild oat head but more upright condensed and narrow.
Ligule
Short to medium: up to 3 mm.
Auricles: Absent
Leaf blade: Long, narrow, rough and sparsely hairy above, or hairless.
Onion couch/False oat-grass ligule. Photo © HGCA.
Onion couch with distinctive swollen bulbous nodules at base of stems. Photo © Blackthorn Arable.
Onion couch/False oat-grass flower heads. Photo © Nigel Caittlin/Alamy.