Weed Seed: Sorghum halepense (Johnson grass)

Family

Poaceae

Common Name

Johnson grass

Regulation

Primary Noxious, Class 2 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.

Distribution

Canadian: Present in ON (Brouillet et al. 2016Footnote 1).

Worldwide: Native range uncertain, possibly native to northern Africa and western and central Asia as far as India (Warwick and Black 1983Footnote 2, USDA-ARS 2016Footnote 3). Widely introduced elsewhere, including eastern Asia, North and South America, Europe, southern Africa, Australia and New Zealand (CABI 2016Footnote 4).

Duration of life cycle

Perennial

Seed or fruit type

Spikelet

Identification features

Size

  • Spikelet length: 3.5 - 6.3 mm
  • Spikelet width: 1.5 - 2.0 mm
  • Caryopsis length: 2.5 -3.0 mm
  • Caryopsis width: 1.5 mm

Shape

  • Ovate-shaped spikelet with two stalks at the base and a pointed top

Surface Texture

  • Glumes are smooth and shiny with teeth near the top

Colour

  • Straw yellow at the tips of the glumes darkening to a reddish-purple at the base
  • Pedicels are straw yellow

Other Features

  • Papery, inert spikelets may be attached to the pedicels
  • Can have light hairs around the pedicels and the base of the spikelet
  • The caryopsis is obovate, reddish-coloured with a large embryo

Habitat and Crop Association

Cultivated fields, pastures, orchards, roadsides and disturbed areas (Darbyshire 2003Footnote 5, CABI 2016Footnote 4). A serious weed of many crops, notably cereals, corn, sorghum, soybeans, beans, cotton, rice, sugarcane, citrus and grapevine (CABI 2016Footnote 4).

General Information

Johnson grass was introduced into the southeastern United States as a forage crop in the early 19th century and then prompted weed control measures in the early 20th century (Warwick and Black 1983Footnote 2).

Johnson grass produces abundant seed (up to 28,000 seeds per plant) which are readily shed when mature and can be carried by wind or rain water (CABI 2016Footnote 4). Seeds can remain viable in the soil for at least seven years (CABI 2016Footnote 4). They also retain their viability after passing through the gut of animals such as birds or cattle (Warwick and Black 1983Footnote 2).

Similar species

Sudan grass (Sorghum bicolor subsp. drummondii)

  • The spikelets of Sudan grass have a similar reddish-purple color, oval shape, hard glumes and pedicels as Johnson grass.
  • Sudan grass spikelets (length: 5.0 - 6.0 mm; width: 2.0 - 3.0 mm) are generally larger than Johnson grass, and the glumes of many spikelets are dark purple . The pedicels of Sudan grass do not have as well-developed cups at the ends as Johnson grass does.

Photos

Johnson grass (Sorghum halepense) spikelets
Johnson grass (Sorghum halepense) spikelet, inner side
Johnson grass (Sorghum halepense) spikelet, outer side
Johnson grass (Sorghum halepense) spikelet base, inner side
Johnson grass (Sorghum halepense) spikelet top showing margin teeth
Johnson grass (Sorghum halepense) caryopsis
Johnson grass (Sorghum halepense) spikelet (L) and caryopsis (R)

Similar species

Similar species: Sudan grass (Sorghum bicolor subsp. drummondii) spikelets
Similar species: Sudan grass (Sorghum bicolor subsp. drummondii) spikelet, inner side
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