Johnsongrass
Sorghum halepense
Washington State Classification
Class A — Eradication Required Statewide
It is considered a weed in all annual agricultural crops, orchards, vineyards, ditches, roadsides and fence rows.
Quick Reference
Identification
Growth Habit
Johnsongrass is a tall, upright, perennial grass, reaching 3 to 10 feet tall in height with an extensive system of rhizomes.
Leaves
The leaves are alternate, from 12 to 30 inches long and ½ to 1 inch wide. It has a noticeable white mid-vein.
Flowers
Flowers clusters (spikelets) in a branching pyramidal cluster (panicle) up to 16 inches. Spikelets grow in pairs at the lower end of this flowering stalk while spikelets are in threes at the upper end. Male and female spikelets appear on the same plant.
Impact
It is considered a weed in all annual agricultural crops, orchards, vineyards, ditches, roadsides and fence rows. When it is under stress, it produces hydrocyanic acid which is toxic to grazing livestock.
Ecology & Spread
Habitat
Johnsongrass is adapted to a variety of soil types, including fertile moist locations such as riparian areas, and also disturbed areas such as old fields and roadsides. Please click here to see a county level distribution map of Johnsongrass in Washington.
Spread Mechanisms
Reproduction
Johnsongrass reproduces by seeds and by rhizomes. Each rhizome segment, or node, can produce shoots and roots. Seeds remain dormant in the soil for several years.
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Control Methods
Mechanical
- Repeated tillage is effective. If tillage is not repeated, preferably monthly, rhizomes can re-sprout and infestation can spread.