Gamba Grass: Legal responsibility and how the pasture became a weed

 

The management of gamba grass was discussed at the recent Douglas Daly Field Day. Weed management officers outlined the legal responsibility of landholders in the containment zone (Class B declaration), which is to reduce growth and spread. This means eradicating isolated plants and new outbreaks. Early detection strategies are required to locate outbreaks, and priority should be given to treating isolated plants and outbreaks along transport corridors and drainage lines.

Gamba grass is a class A weed (to be eradicated) outside of the containment zone (south of the Daly / Katherine Rivers with exceptions in the mid to lower Daly Catchment, and from Kakadu NP eastwards).

People unfamiliar with gamba grass may be wondering why such a productive grass needs to be controlled. Gamba can carry significantly more head of cattle compared to native grasses, and this is why it was so popular. However, it requires a high level of management to remain productive and not become a weed.

Unfortunately it has not always been managed well and has spread to lands where cattle are either not present or are not managed or stocked to deal with such an aggressive pasture. In these situations it produces masses of seed that are able to establish and outcompete native plants on land not managed for cattle. The grass grows to its average height of 3m and the high fuel loads create intense fires, leading to increased tree kills and suppression of woody regrowth and seedling production, and a fire hazard for humans. It is hypothesized that this trend will lead to a change in native vegetation structure from woodland to grassland (an ecosystem transformer), placing pressure on wildlife that depend on trees. Infestations also typically have a significantly reduced diversity of understorey grasses and herbs.

Gamba grass has been declared as a weed to try to stop its continued spread. It currently occupies about 4% of its potential distribution. Gamba is also recognised nationally as a Weed of National Significance and Key Threatening Process due to its ability to degrade ecosystems, reduce habitats and contribute to species decline.

Gamba grass is not a hay species and selling hay with gamba grass seed is now illegal, effectively making it a significant weed of hay paddocks.

Production, sale or purchase, and transport of gamba grass seed is prohibited in the NT.