B.PAS.0003 - Glasshouse assays to determine the role of mealybug and screening of controls

Summary

Pasture Dieback (PD) has emerged widespread across Queensland causing significant impacts to pasture, affecting beef production systems. This project determined the progress of PD from initial infestation with mealybug (in three susceptible grasses) from initial infestation to death of grass, identifying any association with other pathogens that may lead to PD. Screening of potential insecticide controls and dose response bioassays are required to support APVMA applications. This project falls under the Dieback Program Plan which has been set up between DoA and MLA.

Objectives

• Determine and quantify the impact and timing of dieback from initial infestation with mealybug to death of grass.
• Develop a standard bioassay protocol for efficacy assessments of control treatments allowing effective assessment of possible chemical control measures for pasture dieback.
• Conduct efficacy assessments (primarily in glasshouses) of control treatments for mealybug, and collect data that may assist APVMA registration processes.
• Outline at least one draft journal manuscript.
• Provide to MLA periodic information summaries suitable for general media on the role and management of mealybugs in relation to addressing pasture dieback.
• Prepare a two-page summary outlining key facts and findings of mealybugs and how to identify mealybugs causing dieback.

Key findings

This research has identified a window to monitor and then manage mealybugs and reduce the effects of ‘dieback’. Infested grasses, while symptomatic, do not appear to die back until the late summer abundance of mealybugs and wet weather combine to give the apparently sudden ‘dieback’ of grass following late summer rain events.

Benefits to industry

This research has identified a window to monitor and then manage mealybugs and reduce the effects of Pasture Dieback (PD). Infested grasses, while symptomatic, do not appear to die back until the late summer abundance of mealybugs and wet weather combine to give the apparently sudden PD of grass following late summer rain events.

MLA action

Based on the feedback from the Science Review - Dieback workshop (May 2022), MLA has extended this research in a new MDC project with the Queensland University of Technology (P.PSH.1459).

Future research

Monitoring for symptoms and presence of mealybugs from spring (roughly September) through to December can detect early populations. Management such as crash grazing, slashing, or insecticides (if appropriate) can then be targeted at these populations to disrupt the mating and feeding populations in late summer. Detailed work on the timing of management interventions with population biology in the field are required.