Johnson grass

What does it look like?

• Seedlings look like young maize plants both in habit and growth pattern. Mature plants vary in height from 50–300cm.
• Leaf sheaths are ribbed and often hairy on the inner side at the junction with the blade. The leaf blades are flat, alternate, and can reach up to 90 cm in length and 2–5 cm in width. The underside midrib is whitish in colour.
• Seed is the primary means of dispersal. However, rhizomes—underground, root-like stems—can also spread easily through cultivation. Even a small fragment of rhizome is enough to generate a new plant. Both rhizome pieces and seeds can be transported to new locations on cultivation and harvesting equipment.

Why is it a problem?

Johnson grass is considered one of the world's 10 worst weeds and has the potential for major economic impacts on pastoral farming and cropping. This plant is aggressive and forms dense spreading patches, often out-competing other grasses and crops. In some conditions, Johnson grass is toxic to stock and is a fire hazard. Establishment of Johnson grass would see increased labour costs to control weeds, reduced yields for many arable crops, and reduced net farm income.

Control methods

Johnson grass is under an eradication programme led by MPI. Biosecurity New Zealand works closely with regional councils and Department of Conservation on these programmes.

More information

In 2021, Johnson grass was detected in the Auckland region, marking its first recorded presence in New Zealand in over a decade.

Related links

• Stopping the spread of Johnson grass | NZ Government
• Johnson grass • Weedbusters
• National Interest Pest Responses programme