B.PAS.0513 - Management options and species evaluation to increase prodoductivity in dieback affected pastures - PHASE II

Summary

Pasture dieback has resulted in the death of large areas of previously productive grazing country in Queensland and, more recently, northern NSW. The cause of dieback, pasture mealybug (Heliococchus summervillei), causes reduced pasture health and death.

Legumes are not affected by pasture dieback, and some grass species appear to tolerate its effects. Four field trials established in 2021 demonstrate that combinations of stick raking or cultivating and re-sowing with a grass pasture or pasture/legume mix greatly improved productivity compared to untreated areas that were left to regenerate naturally, or those resown with the pre-existing grass species (i.e. buffel or bisset).

Trials show that stick raking is a viable option for preparing a seed bed in locations that are not particularly weedy, or do not have a large bulk of pre-existing grass. Grass mixes and grass and legume mixes appear to be providing good coverage in dieback sites; however, they will require longer term studies to assess the long-term impact of Dieback on these treatments compared to control plots.

Variety trials have identified that both Mekong brizantha and Humidicola are tolerant to dieback.

Objectives

The broad aim of this project was to rigorously evaluate altered pasture management in dieback-affected areas and communicate the results to producers. Specifically, the project aimed to:
- Identify and evaluate economically viable pasture management options: Increase pasture productivity and produce feed for livestock in dieback-affected Queensland grazing regions.
- Identify and evaluate tolerant pasture species or varieties: Find pasture species or varieties that are tolerant to pasture dieback
- Communicate results and recommendations: Share findings and recommendations with producers through a producer’s guide, field days, factsheets, and other communication methods.

Key findings

Assessment of the field trial sites demonstrated that treatments using stick raking or cultivation and resowing with a pasture grass and/or grass and legume mix generally gave the best results in useful plant coverage. Stick raking or cultivating and allowing for natural regeneration resulted in a higher weed incidence, and greater dieback expression. This was a consistent trend across all trial sites.

Pasture grass and grass and legume mixes gave the best results by minimising dieback expression and providing good, useful coverage. The weediness of an area may impact the effectiveness of these treatments and needs to be considered when sowing legumes due to constraints of managing forbs.

Application of fertiliser has not impacted dieback susceptibility, however, it supported an initial increase in biomass.
Variety trials have had varying degrees of seed germination and resulting success of pasture establishment. Low seedling numbers in some varieties are the result of poor-quality seed. Further assessments are required to better assess the impact of dieback on these varieties.

Benefits to industry

One of the most promising strategies identified is sowing pasture mixes with more tolerant grass species into dieback-affected areas and including legumes in the mix. Additionally, the trials have identified and tested commercially available grass species with strong tolerance to the pasture mealybug.

These findings offer producers practical, immediate solutions to mitigate the impact of dieback and enhance pasture resilience.

MLA action

Its recommended that all four trial sites continue to be monitored for at least another two years to assess long term performance and persistence of varieties and treatments in the different soil types and climatic conditions.

Future research

Based on the project's results, it is recommended to extend the project to provide a robust basis for recommending replanting and renovation strategies.
The trial sites should be used as demonstration sites to showcase effective practices to the broader industry, leveraging networks like MLA, DAFQ and AgForce for dissemination.

Lastly, a comprehensive communication strategy should be implemented to share findings through field days, factsheets, and updates to the MLA Pasture Dieback Management Guide.