Johnson grass

Johnson grass is a tufted perennial summer grass that can grow to three metres tall.

Description

• Leaves are smooth, flat, and alternate. Alternate leaf blades are often purple-splotched.

• Flowerheads are 50cm long, hairy, purplish, and pyramid shaped.

• Rhizomes are fleshy and creeping, growing down to one metre deep.

• Seeds are dispersed by the wind, water, and animals. Vegetatively spread via rhizomes.

• Habitats include open areas, forest and riparian margins, pasture, crop land, wasteland, and roadsides.

What you need to know

Johnson grass forms dense infestations, smothering native vegetation and crops. It is allelopathic and toxic to livestock.

Management approach

Johnson grass is declared an unwanted organism by the Ministry for Primary Industries (MPI) because it is capable of causing harm to the natural environment, physical resources or human health in Aotearoa/New Zealand.

These species pose a high risk to our environment, economy, recreation, and cultural values.

Rules

Any species declared a pest cannot be sold or be in a place where plants are being sold. Pest plants cannot be propagated, bred, multiplied, communicated, released, caused to be released, or otherwise spread.

Control

Do not attempt to undertake control of Johnson grass yourself. Report sightings to the MPI on Exotic Pest Hotline at 0800 80 99 66 or the online reporting form.