Know Your Weeds: High Biomass Grasses

WHAT ARE THEY?

High biomass grasses, like Gamba grass (Andropogon gayanus), Guinea grass (Megathyrsus maximus), grader grass (Themeda quadrivalvis), thatch grass (Hyparrhenia rufa) and giant rats tail grass (Sporobolus pyramidalis and Sporobolus natalensis), are introduced grass species that grow rapidly and produce large amounts of vegetation.

These grasses were often introduced accidentally or as pasture grasses for grazing but have become invasive after escaping from cultivation.

WHY ARE THEY A PROBLEM?

High biomass grasses outcompete native vegetation, reduce biodiversity, and alter fire regimes. Their high biomass creates huge fuel loads which generate intense fires that can destroy ecosystems, threaten wildlife, and damage property.

They also invade agricultural lands, reducing productivity and significantly increasing management costs. Many species are not palatable to stock so they can have a two way impact on pastures.

HOW TO SPOT THEM

Look for tall, dense grasses with distinctive seed heads and rapid growth. High biomass grasses can dominate disturbed areas, roadsides, and pastures. They may initially turn up in places where materials like soil have been imported from other areas, or where seed has fallen off vehicles, machinery, raw materials or animals.

Early detection is the key to prevent more seed being added to the system.

CHARACTERISTICS 

Gamba Grass 
A large perennial grass which grows up to 4m tall, forms dense tussocks, and has broad leaves with a white midrib.

Guinea Grass 
A large tufting perennial grass which reaches 3m in height, with long, narrow leaves and pyramid-shaped seed heads.

Grader Grass

An annual tufted grass up to 2m tall, with distinctive reddish-brown stems and fan shaped seed heads.

Thatch Grass 
A perennial grass up to 3m tall, with smooth leaves and tangled, thatchlike tufts and long stems with distinctive dark bands.

Rats Tail Grasses 
Rats tail grasses such as giant rats tail grass have distinctive cylindrical seed heads and tough, rasp like leaves which make them unpalatable to stock and other grazing animals.