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. 2016^Footnote 1).

Worldwide: Native range uncertain, possibly native to northern Africa and western and central Asia as far as India (Warwick and Black 1983^Footnote 2, USDA-ARS 2016^Footnote 3). Widely introduced elsewhere, including eastern Asia, North and South America, Europe, southern Africa, Australia and New Zealand (CABI 2016^Footnote 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 2003^Footnote 5, CABI 2016^Footnote 4). A serious weed of many crops, notably cereals, corn, sorghum, soybeans, beans, cotton, rice, sugarcane, citrus and grapevine (CABI 2016^Footnote 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 1983^Footnote 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 2016^Footnote 4). Seeds can remain viable in the soil for at least seven years (CABI 2016^Footnote 4). They also retain their viability after passing through the gut of animals such as birds or cattle (Warwick and Black 1983^Footnote 2).

Similar species

Sudan grass (Sorghum bicolor subsp. drummondii)

• The spikelets of Sudan grass have a similar reddish-purple colour, 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

Similar species