B.ERM.1105 - Indian couch invasion: scope, production impacts, and management options

Summary

There is widespread producer concern about the potential of Indian couch to significantly reduce carrying capacity and accordingly options for its management and control are needed. This project aimed to address these concerns by quantifying the extent of invasion and helping producers identify management/control options.

Indian couch mapping was conducted for grazing lands of eastern Queensland. An area of 9.6 million hectares, representing ~32% of the total area that makes up the Burdekin, Fitzroy, and Burnett-Mary catchments, was identified as being at risk of Indian couch dominance.

The project identified management options to prevent the spread of Indian couch include avoiding over-utilisation of the pasture, maintaining high ground cover, and improving the competitiveness of existing pasture species. For pastures dominated by Indian couch, key strategies for improved production and ecological function include reducing stocking rates, applying more rest to pasture, and incorporating new grasses and legumes into the pasture where possible.

Objectives

Research objectives included:

• Identify the factors responsible for Indian couch expansion.
• Determine the extent and likely spread of Indian couch invasion in north and central Queensland.
• Determine the impacts of Indian couch on production and landscape function.
• Conduct preliminary research into control options.
• Identify and test best-bet management options to either manage or control the spread of Indian couch on native and sown pastures.

Key findings

A range of factors are contributing to the spread of Indian couch, such as land degradation, heavy grazing, prolific seed production and means of spread, and climatic extremes in rainfall variability. The spatial mapping of Indian couch identified that the combined area of the at-risk land types equated to 9.6 million ha: ~6.6 million ha for the Burdekin, ~0.7 million ha for the Burnett-Mary, and ~2.3 million ha for the Fitzroy.

The project identified management options to prevent the spread of Indian couch include avoiding over-utilisation of the pasture, maintaining high ground cover, and improving the competitiveness of existing pasture species. For pastures dominated by Indian couch, key strategies for improved production and ecological function include reducing stocking rates, applying more rest to pasture, and incorporating new grasses and legumes into the pasture where possible.

The project results were consistent with producer experience that Indian couch can be an acceptable feed source in certain seasons, but overall Indian couch is a less reliable feed source, particularly in drought seasons.

Indian couch seed was shown to be less tolerant of heat compared to Black speargrass which has implications for the potential role of fire in Indian couch management. A seed persistence study showed that Indian couch seed should be classified as long-term persistent (three plus years), similar to native species.

Benefits to industry

The project has addressed a knowledge gap and developed maps to demonstrate the current extent and potential future spread of Indian couch in Queensland’s grazing lands.

Candidate management and control options for Indian couch have been identified for producers in two scenarios:
- managing existing Indian couch pastures
- halting/reducing/removing Indian couch in native and sown pasture.

For pastures with highly dominant Indian couch, key strategies for improved production and ecological function include reducing stocking rates, applying more rest to pasture (e.g., wet season spelling), and incorporating new grasses and legumes into the pasture where possible.

MLA action

MLA is using the outcomes of this project to inform new investments and create adoption material.

Future research

A range of areas demanding further research attention can be suggested, as summarised below according to objective.