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
Management Programme
Notifiable Organism
Some organisms must be notified to MPI if they're spotted in New Zealand. These include serious pests and diseases like foot-and-mouth disease, the rabies virus, fruit fly and disease-carrying mosquitoes. If a notifiable organism established in New Zealand, it could severely affect our primary production or trade and market access. If you spot a notifiable organism, you have a legal obligation under section 44 of the Biosecurity Act 1993 to tell MPI. Call the pests-and-diseases hotline on 0800 80 99 66.
The Biosecurity (Notifiable Organisms) Order 2016 lists notifiable organisms. New additions can be made by the Governor-General and MPI periodically reviews the list to ensure it is up-to-date.
Unwanted Organism
An unwanted organism is any organism that's capable of causing harm to natural or physical resources (like forests and waterways) or human health. A number of introduced pests in New Zealand are classed as unwanted.
National Interest Pest Responses programme (NIPR)
Nine harmful weeds are managed under the National Interest Pest Responses (NIPR) programme. These pests could cause serious harm to New Zealand's environment and economy if they are allowed to spread.
More informationTaxonomies
FamilyPoaceae
TypePlants
GroupGrass
HabitatLand
Management ProgrammeNotifiable OrganismUnwanted OrganismNational Interest Pest Responses programme (NIPR)
