Ontario Weeds: Johnson
Table of Contents
- Other Names
- General Description
- Stems and Roots
- Flowers and Fruit
- Similar Species
- Related Links
Name: Johnson grass, Sorghum halepense
Other Names: sorgho d'Alep, sorgho de
Family: Grass Family (Gramineae)
General Description: Perennial reproducing
by seed and by large, coarse underground stems (rhizomes).
Photos and Pictures
Johnson grass (A - infestation in field; B - large
whitish rhizomes produced after plants head out).
Johnson grass. A. Young plant growing from seed; The "mother
seed" still attached to the primary root. B. Older plant
growing from up-turned tip of phizome. C. Base of mature plant.
D. Panicle. E. Leaf-base. F. Cluster of 3 fertile (seed-beaing)
and 4 sterile (non-seed bearing- spikelets.
Stem and leaf-base characteristics of a typical grass.
Stems & Roots: Stems 50-270cm
(2-9ft.) tall, 5-20mm (1/5-4/5in.) in diameter, smooth and stiff
or wiry; leaves 20-60cm (8-24in.) long, 1-2cm (2/5-4/5in.) wide,
bright green, and smooth; leaf sheaths split with smooth overlapping
margins; ligule membranous, 2-5mm (1/12-1/5in.) long; no auricles;
collar (junction between leaf blade and leaf sheath) often with
purplish blotches on its sides; rhizomes thick and fleshy, at first
white to pinkish, but turning chestnut brown over winter, as much
as 1cm (2/5in.) in diameter and up to 1m (40in.) long, with many
nodes and inter-nodes, frequently rooting from the nodes, and the
internodes partially covered with brown scale-like sheaths.
Flowers & Fruit: Inflorescence
up to 50cm (2ft.) long, with whorls of upright branches; at first
compact, later spreading and open; spikelets arranged in pairs at
each node along the thin branches, 1 member of the pair is sterile
(non-seed bearing), rather dull in texture and has a short stalk;
the second member of each pair is fertile (contains the grain or
"seed"), rather plump, about 5mm (1/5in.) long by 2.5mm
(1/10in.) wide, does not have a stalk, and may have a twisted awn
1-1.5cm (2/5-3/5in.) long. Flowers from July to September.
Habitat: Johnson grass is presently
known to occur in 13 counties in southern and southwestern Ontario.
Similar Species: Young plants of Johnson
grass might be mistaken for very thin plants of corn, Sudan grass,
or an annual grain sorghum. They can be distinguished from corn
by the size and shape of the mother seed attached to the primary
root of the seedling, or if growing as a shoot from an overwintered
rhizome, by the presence of the thick, hard, brownish rhizome. Older
plants can be distinguished by their large, open, non-silky inflorescences
with plump seeds, and in autumn by the presence of coarse, whitish,
rope-like, branching rhizomes (horizontal underground stems) about
1cm (2/5in.) in diameter in late autumn. Most rhizomes are killed
by Ontario winters, but 2 or 3 stands are apparently hardy enough
that their rhizomes are not killed, and these plants are acting
as true perennials. Also compare with Common
... on general Weed
... on weed identification, order OMAFRA
Publication 505: Ontario Weeds
... on weed control, order OMAFRA
Publication 75: Guide To Weed Control
to the Ontario Weeds Gallery |