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Johnson Grass

Johnson Grass

Johnson grass2

Johnson grass3

Common reed plant

Common reed seed head

Giant reed plant

Giant reed infestation

Giant reed flowers

Giant reed flower spike



Johnson grass (Sorghum halepense) is listed as noxious in class 4 in Upper Lachlan and Southern Slopes LCAs in the Southern Tablelands and South East Region.


Johnson grass is a robust perennial grass to 1.5 metres in height, which has underground runners (rhizomes). Leaves are 20-50cm long and 5-20mm wide, flat and hairless, with a prominent midrib and roughened margins. The flowering stems are 10-35cm long, with spreading branches. Flowers are green to purple. The photos of Johnson grass were provided by Forest & Kim Starr, USGS, Hawaii. This is a subtropical species which prefers moist soils. In NSW it is prominent on the north coast and may be weedy in irrigation areas .


Seed sticks to animals and clothing, and passes through animal guts intact, to be spread in droppings. They may also be spread in contaminated hay.
It may also be spread in soil on vehicle tyres and machinery, and as a contaminant of agricultural produce such as hay or grain. Locally plants spread by rhizomes, and pieces of rhizome may be spread during cultivation or roadworks.


Columbus grass (Sorghum x almum) is a hybrid of Johnson grass and grain sorghum (Sorghum bicolor). It is similar in appearance, but even larger, growing up to 3.5 metres high. It is listed as noxious in class 4 in the same LCAs.

The native common reed (Phragmites australis), which grows in wet areas, either in or adjacent to water, has a similar erect leafy appearance, but the seed heads are a cohesive fluffy clump rather than having obvious branching.

Giant reed (Arundo donax) is a little similar, but more bamboo-like in appearance.  It is sometimes planted as an ornamental or for bank stabilisation, but has considerable weed potential in wet areas.  Although not listed as noxious, it should not be planted.


Dig or spot spray new infestations before seeding. Once a dense infestation has developed, repeated cultivation to exhaust the rhizomes or an integrated control program using cultivation, competing crops and herbicides may be needed. Grass-specific herbicides can control it in broadleaf crops. In difficult terrain where cultivation is not feasible herbicides are the only possible method. Burn or slash first to reduce bulk and spray regrowth in mid to late summer.