Confronting Pasture Dieback: Challenges and Solutions for Queensland’s Pastoral Industry

Pasture dieback has rapidly expanded throughout Queensland and is now affecting regions into New South Wales, including areas as far south as western Sydney. Initially observed in buffel grass pastures of Central Queensland during the 1990s, the spread intensified considerably post-2015, impacting Southeastern Queensland’s pastures by 2018 and extending into the inland and south-west regions in recent years.

According to Queensland DPI pasture specialist Ted Callanan, who spoke at the recent BeefUp forum in Morven, the dieback phenomenon has predominantly followed the patterns of sown pasture systems in conjunction with rainfall dynamics. Fortunately, native pastures remain largely unaffected.

Unraveling the Causes of Pasture Dieback

While the link between pasture dieback and the native sap-sucking mealy bug Heliococcus summervillei is well established, the precise mechanisms behind plant mortality are still being investigated. Callanan posits that the mealy bug compromises grass health by feeding on sap, making plants more susceptible to additional stressors, including diseases and adverse weather conditions.

“While the mealy bug consistently appears alongside pasture dieback, its role as the causative agent behind plant death remains uncertain,” Callanan noted. Understanding that these bugs primarily spread through wind helps elucidate the rapid geographical expansion of dieback.

International Research Initiatives

The ongoing spread of mealy bugs in several American states has prompted increased attention and research, with experts from the USDA and the Smithsonian Institute now studying these pests. Callanan expressed hope that collaboration on a global scale could lead to solutions for managing the bug’s proliferation in Australia.

Assessing Pasture Vulnerability

The affected regions exhibit varying levels of vulnerability among tropical sown pasture species. While commonly planted short-growing buffel varieties like American and Gayndah are prone to dieback, taller strains such as Biloela buffel demonstrate greater resilience.

Callanan highlighted instances where entire paddocks of susceptible varieties were decimated, leaving only patches of the more robust Biloela buffel grasses. Such observations underscore the importance of species selection in managing pasture health.

Implementing Effective Management Strategies

To counteract dieback, Callanan suggested several strategies to reduce risks and maintain productivity:

• Grazing Management: Adjusting grazing to reduce biomass can effectively lower mealy bug populations. Early grazing of susceptible grasses, even when they show signs of damage, may extend their viability.
• Diversifying Pastures: Introducing resilient species and legumes, such as Desmanthus, enhances pasture resilience and productivity.
• Sowing Break Crops: Replacing susceptible grasses with break crops can aid in containing dieback risks.
• Focus on Recovery: While managing pastures for recovery is key, Callanan warned that natural re-establishment can still leave pastures vulnerable to reinfestation.
• Controlling Mealy Bugs: Current chemical options are limited, and attempts at burning have proven ineffective.

Case Studies: Lessons Learned

Case studies illustrate the dual nature of challenges presented by pasture dieback, as well as viable approaches to managing it. One instance in South East Queensland demonstrated recovery potential after a 2019 dieback incident, with weed management leading to significant regeneration within two to three seasons. However, the persistent risk of reinfestation remained a concern.

In another example on the Frith family’s Glen Arden property in Roma, integrating Desmanthus into previously affected paddocks proved effective in counteracting dieback, while surrounding paddocks with more tolerant Biloela buffel maintained their productivity. “Legumes enhance carrying capacity, weight gain, and soil health, creating a multitude of benefits,” Callanan remarked.

Looking Forward: Embracing Opportunities Amid Challenges

Despite the complexities surrounding pasture dieback, Callanan emphasized that opportunities exist to enhance overall pasture management. “Take a step back, assess your paddock, and consider what improvements can be implemented. Renovating and restoring productivity is not only possible but essential.”

In navigating the ongoing threat of pasture dieback, the agricultural community can explore innovative solutions and methods that bolster pasture resilience, ensuring the longevity of Queensland’s pastoral industry.