Weed Seed: Avena sterilis (Sterile oat)



Common Name

Sterile oat


Secondary Noxious, Class 3 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.


Canadian: Occurs in ON (ephemeral); previously reported from QC but currently excluded from the flora (Brouillet et al. 2016Footnote 1).

Worldwide: Native to southern Europe and the Mediterranean region; associated with the cultivation of oats (CABI 2016Footnote 2; USDA-ARS 2016Footnote 3). Widely introduced elsewhere and present on all continents except Antarctica (CABI 2016Footnote 2; USDA-ARS 2016Footnote 3). Occurs in the United States, in: CA, CO, NJ, OH, OR, PA (Kartesz 2011Footnote 4, USDA-NRCS 2016Footnote 5).

Duration of life cycle


Seed or fruit type

Pair of florets

Identification features


  • The first floret length: 10.0 - 27.0 mm
  • The first floret width: 2.5 - 4.0 mm
  • The second floret length: 10.0 - 14.0 mm
  • The second floret width: 2.0 - 2.5 mm
  • Caryopsis length: 10.0 mm
  • Caryopsis width: 2.0 - 2.5 mm


  • Floret elongate, tapers at top into long, papery lemma extensions

Surface Texture

  • Floret pebbled texture
  • Long, stiff reddish hairs around base of the floret
  • The lemma tends to have sparse hairs, but can be removed during processing


  • Florets tend to be reddish colour with straw yellow tips, but can be solid straw yellow

Other Features

  • Florets usually shed as a pair, but may detach during processing
  • Callus at base of the first floret is prominent and elongated, the callus of the second floret is peg-like
  • A strongly bent and twisted awn is attached to upper half of lemma; up to 80.0 mm long

Habitat and Crop Association

Cultivated fields, roadsides and disturbed ground. A serious weed of arable crops, particularly cereals, with a life cycle that mirrors many annual crops. Often occurs on heavier soils, sometimes replacing the similar species A. fatua in this soil type where the two co-occur (CABI 2016Footnote 2).

General Information

Like wild oat, sterile oat has been dispersed around the world as a contaminant in cereal grain and seed, as well as on agricultural equipment, straw, hay, livestock and wool. A crop mimic in Avena sp. (oat) crops, it produces seeds that are difficult to separate from grain (CABI 2016Footnote 2).

Individual plants can produce up to 200 seeds, although the average in a natural population has been reported as 13-21 seeds per plant; seeds remain viable for up to 5 years in the soil (CABI 2016Footnote 2).

Similar species

Wild oat (Avena fatua)

  • Wild oat florets are a similar elongated shape, reddish colour, presence of callus hairs, prominent callus, and twisted awn.
  • Wild oat florets (length: 10.0 - 15.0 mm; width: 2.5 - 4.0 mm) are generally shorter, have a longer callus, not shed in pairs and the papery lemma tips are not as prominent as in sterile oat.


Sterile oat (Avena sterilis) reddish florets
Sterile oat (Avena sterilis) yellow florets
Sterile oat (Avena sterilis) floret, palea view
Sterile oat (Avena sterilis) floret, lemma view
Sterile oat (Avena sterilis) floret, palea view
Sterile oat (Avena sterilis) florets
Sterile oat (Avena sterilis) floret, lemma view

Similar species

Similar species: Wild oat (Avena fatua) florets and caryopsis
Similar species: Wild oat (Avena fatua) floret, palea view
Similar species: Wild oat (Avena fatua) floret, lemma view
Similar species: Wild oat (Avena fatua) floret, side view
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