Johnson grass
Sorghum halepense
Status: Notifiable Organism, Unwanted Organism
Description
Johnson grass a native of the Mediterranean (Southern Europe, North Africa and Western Asia), is a robust, aggressive, perennial, summer grass capable of forming dense thickets that exclude most other plants.
Seedlings are very similar to young maize plants both in habit and growth pattern. Mature plants vary in height from 500 – 3000 mm. Leaf blades are flat, alternate up to 900mm long and 20 – 50 mm wide. The midrib on the underside is whitish. Leaf sheaths are ribbed and often hairy on the inside of the junction with the blade.
Impact
Johnson grass is considered to be one of the world's ten worst weeds and one of the five worst weeds in New Zealand. It could have a major economic impact on New Zealand agriculture should it establish in this country. The plant forms dense spreading patches that compete vigorously with other plants often out competing grasses and crops. Pieces of rhizome and seed may contaminate cultivation and harvesting equipment and be consequently transported to new sites. Establishment of Johnson grass would see increased labour costs to control weeds, reduced yields for most crops, and reduced net farm income. However, active management at all known sites has restricted the potential impacts of this plant in New Zealand.
Where is it found?
Johnson grass has been found from Northland to Canterbury. Sixty five of the known sites of Johnson grass are now considered eliminated, having been clear of the plant for at least seven years and three further sites have been clear of plants for at least two years. One site is active.
What to do
Propagation, spread, and sale of Johnson grass is prohibited under the Biosecurity Act 1993. All sightings must be reported to MAF Biosecurity New Zealand on 0800 80 99 66.
MAF contracts a monitoring and control programme aimed at eliminating Johnson grass from New Zealand.
Please also see the johnson grass fact sheet 
(247 KB).
Page last updated: 18 August 2009