Johnsongrass, a coarse and generally clumping grass, is one of the most troublesome of perennial grasses. It rapidly produces colonies, is very competitive with crop plants, and is especially a problem in California cotton fields. In California, johnsongrass is found in the Central Valley, Cascade Range foothills, Western California, and the Sierra Nevada foothills to about 2600 feet (800 m). It inhabits agricultural land, and other disturbed sites. Johnsongrass hybridizes with grain sorghum (milo). Under certain conditions, the leaves of johnsongrass (and sorghum) can produce toxic amounts of hydrocyanic acid, which can poison livestock when ingested. It is a highly variable species with some regional biotypes.
Habitat
Orchards, vineyards, ditchbanks, disturbed sites, roadsides, fields, and agronomic and vegetable crop fields.
Seedling
Although it resembles a young corn seedling, a johnsongrass seedling can be distinguished by its football- to egg-shaped, dark reddish-brown to black seed, which remains attached after carefully removing the seedling from soil. The first leaf blade is parallel to the ground. Leaf blades are hairless with smooth edges and have a midvein that is whitish at the base.
Mature Plant
Mature johnsongrass grows in spreading, leafy tufts with shoots (tillers) sprouting from the base (crown). Stems stand erect, from 6 to 7 feet (1.8–2.1 m) tall, and are unbranched. Leaves are rolled in the bud. The blade is flat, hairless to sparsely hairy, especially near the ligules. Sheathes are open, hairless to sparsely hairy near the collar, and pale green to reddish. The leaf has a prominent whitish midvein, which snaps readily when folded over. Underground stems are thick, fleshy, and segmented. Roots and shoots can sprout from these segments.
Collar Region
Ligules are membranous and generally have a fringe of hairs at the top. There are no auricles.
Flowers
Flowers bloom from May through October. The flower head is large, open, well branched and has an overall pyramid outline. Initially it is green or greenish violet. At maturity it becomes a dark reddish or purplish brown.
Reproduction
Reproduces by seed and underground stems.
Related or Similar Plants
- Fall panicum, Panicum dichotomiflorum
