B.PAS.0506 - Determining the role of ground pearls in Pasture Dieback

Summary

The aim of this project was to determine the role of ground pearls in pasture dieback. Multiple surveys were conducted of symptomatic and asymptomatic sites, and hundreds of soil samples were processed using a methodology developed in this project. Ground pearls were found in approximately 75% of pasture dieback sites examined, but they were also present and absent in asymptomatic sites and were absent in 25% of symptomatic sites. As they do not readily move in the soil, and were absent from multiple pasture dieback sites, if pasture dieback is caused by a single agent, they cannot be the primary cause. Molecular characterisation indicated the presence of four ground pearl species in Australia. A molecular diagnostic for ground pearl detection and identification was developed that can streamline soil processing and be applied to archived soil samples. There is now much greater awareness of ground pearls among producers, and scope to better characterise their impacts and develop effective integrate management plans.

Objectives

1. Confirm and quantify the presence of ground pearls at pasture dieback sites.
2. Assess the impact of ground pearls on a range of host plant species.
3. Molecular characterisation of ground pearl populations.
4. Develop an integrated Pest Management program for ground pearl.

Key findings

• At least three species of ground pearls occur within Queensland pastures, while a fourth species might also be having impacts.
• They are not consistently associated with pasture dieback, and so cannot be the primary cause if pasture dieback has a single cause.
• They are present in some areas of pasture dieback where no other cause is apparent, so it is possible they may be causing localised plant death.
• Molecular assays have been developed that can identify and differentiate ground pearls present in soil.
• The role of environmental conditions needs to be understood in order to improve management of pasture dieback in the future.

Benefits to industry

This work has largely discounted the potential that ground pearls are a primary cause of pasture dieback, which in itself is an important finding because it removes a live lead. However, there are broader industry benefits. Until this work the industry was largely unaware of the presence of ground pearls in pastures, but now producers can investigate unthrifty pastures and potentially identify ground pearls where they are present. Ground pearl detection and identification will be streamlined by the development of DNA tests, while several targets for improved ground pearl management have been identified.

MLA action

The Pasture Dieback Management Guide will be updated to reflect the new insights and knowledge regarding ground pearls and causes of pasture dieback.

Future research

Further research on these cryptic pests are warranted because we now know they are widespread, but we do not know what they are costing us.