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Statewide IPM Program, University of California

Shattercane  (Sorghum bicolor)

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Life stages of shattercane inflorescence collar and sheath flowering stems florets (seeds inside)

Shattercane is a summer annual grass descended from wild and cultivated sorghum varieties; it is commonly called “sorghum” in some circles. In California it is found in the deserts, Central Valley, North Coast Ranges, and coastal regions, to almost 2000 feet (600 m).

Like its close relative, johnsongrass, shattercane has many regional biotypes, grows rapidly, and competes aggressively with crop plants significantly reducing yield. Shattercane readily hybridizes with johnsongrass and both species freely cross with commercial sorghum cultivars, reducing the quality and value of harvested seed. Fungi, bacteria, and nematodes can infect weedy sorghums and then cause agricultural problems. Weedy sorghum serves as an alternate host to pests such as sorghum midge, Contarinia sorghicola, and viruses causing sugarcane mosaic, maize chlorotic dwarf, and corn stunt.

Shattercane and johnsongrass can provide wholesome forage for livestock, however, once exposed to frost, drought, trampling, or herbicides, leaves of both species can manufacture levels of hydrocyanic acid that can be poisonous to livestock when ingested. Under some conditions, plants accumulate toxic levels of nitrates. At maturity some plants “shatter”, or shed many flowers (spikelets), hence its common name.

Habitat

Shattercane is found in fields, agronomic and vegetable crops, disturbed sites, roadsides and especially grows on fallow fields. It grows best in warm temperate to subtropical areas on well-drained, fertile soil where warm-season moisture exists, but can tolerate hot, dry conditions.

Seedling

Shattercane resembles a corn or johnsongrass seedlings and it is indistinguishable from commercial sorghum until the flowering stage. Careful removal of the seedling and examination of the attached seed will confirm whether or not it is corn. Shattercane and johnsongrass seeds are similar: football- to egg-shaped and dark reddish-brown to black. However, seeds of johnsongrass are narrower, mostly 1/16 to 1/12 inch (1.5–2 mm) wide, whereas those of shattercane are wider, mostly 1/10 to 1/6 inch (2.5–4 mm). Shattercane leaves are rolled in the bud. If the first blade is parallel to the ground the seedling is more likely johnsongrass and not shattercane.   

Mature plant

Shattercane resembles grain sorghum and corn. It is a coarse grass that usually grows in tufts and reaches almost 7 feet (2m) tall. Stems are erect, round to slightly compressed in cross-section, unbranched, with solid internodes, and sometimes, purplish spots. Leaves are bright green with a noticeable white midvein. They grow to 3-1/3 feet (100 cm) long, 1-1/5 to 4 inch  (3–10 cm) wide, and are hairless to slightly hairy, particularly near the ligule. Leaf edges are rough. Sheaths are open, pale green to reddish, ribbed, hairless or slightly hairy at the collar. Tillers grow from the crown. Johnsongrass leaves are overall shorter, up to 2 feet (60 cm) long and 1/5 to 1-1/5 inch (0.5–3 cm) wide. Robust, coarse rhizomes are found at the base of johnsongrass plants, but not in shattercane.

Collar

The collar is wide, smooth, and pale green or whitish. Auricles are absent.

Flowers

Flowers bloom from May through October. Generally the flower clusters (inflorescences) form dense, compact, and stiffly upright flowering branches (panicles). Occasionally the branches are open, and the inflorescence has more of a pyramid shape and droops at the top. Initially the inflorescences are pale green or violet green that frequently mature into dark reddish or purplish brown. Mature johnsongrass flowering branches are characteristically open and pyramid shaped. Shattercane panicles range from 3-1/5 to 20 inches (8–50 cm) long.

Seeds

Shattercane plants can yield up to 2000 seeds per panicle generally producing more seeds than johnsongrass.

Reproduction

Shattercane reproduces by seed.

Related or similar plants

  • Commercial sorghum (also Sorghum bicolor)
  • Johnsongrass, Sorghum halepense

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