Pasture dieback: research activity update

Find out what pasture dieback research activity is currently underway as part of MLA’s effort to identify potential causes and develop effective management strategies.

Identification – remote sensing

The scale of grasses affected by dieback is difficult to accurately measure and currently relies on numerous property visits and investigations. The below research areas aim to increase correct identification of dieback and speed up the complete process. This will enable faster, more accurate responses to new and existing dieback-affected areas. 

• Satellite imaging
  • Historically examining known dieback outbreaks, combined with GPS locations and local graziers’ recollections are used to build algorithms for computer-based detection systems. The greater the number of properties examined, the greater the accuracy of the system.  
  • The completion of the first phase of properties to be examined has been completed. This leads to the build of a “trend pattern” that can be applied to other properties.
  • Trend patterns points towards the weather (rain) having a direct effect on dieback. It appears that non-flooding rainfall seems to increase the risk of dieback. 
  • Further properties need to be examined to build greater confidence in the system.
  • Results will be used to identify affected areas, spread patterns and predict new outbreaks.
• Hyperspectral imaging
  • Special highly sensitive camera that can see 270+ bands (human eye sees in three bands) have been used to analyse dieback-affected grasses. The goal is early detection, so management measures can be taken.
  • Hyperspectral imaging is used in a number of agriculture areas for detection of plant disease from grapes to forest trees (normally via drone).
  • Laboratory work shows encouraging results for positive identification of early detection of dieback.
• Volatile organic compounds – chemical fingerprinting
  • Reports that cattle seem to avoid grasses affected by dieback lead to the theory that there must be some smell coming off the plant, which humans can’t smell.
  • University systems available at Queensland University of Technology IFE to detect extremely small chemical particles known as VOC (volatile organic compounds) which could be detected by cattle, have been examined.
  • A number of affected and healthy plants have been analysed under laboratory conditions to attempt to isolate the “dieback smell” and are starting to show encouraging results on positive identification.
  • This could help with early detection in the paddock.
• Mealybug identification
  • Work is continuing on the exact species identification and differences to historically-listed mealybug (1926 and 1978 in Queensland) that was responsible for pasture dieback in paspalum and other pasture grasses.  
  • This is to identify if this mealybug is a native or from another country.

Metagenomics – DNA analysis of fungi and bacteria from soil, root and leaf samples

• Research is aiming to compare the board microbial communities with relation to ‘healthy’ verses ‘affected’ American Buffel plants using leading edge DNA sequencing methods. This will identify what microbes are involved in pasture dieback.
  • Initial Next Generation Sequencing completed
    • Data has been validated and is ready for microbial comparison with final samples.
  • Final sampling completed – sequencing due for completion mid-December.
  • Comparison analysis due by March 2019.

Mealybugs – leading potential causal agent

• Life history and breeding patterns (critical)
  • This is critically important in understanding lifecycle and what the best control methods are.
  • It’s also important for understanding how they breed, how long eggs can last for underground etc, do they have natural enemies (these can be used to control them).
• Bioassays and screening treatments (critical)
  • Now that mealybugs are said to be the leading cause of dieback, a number of controlled experiments can be performed. These are called bioassays and screening is the testing of treatments in a controlled manner.
  • Breeding a variety of typical pasture grasses for bioassays and screening.
  • Glasshouse testing of potential treatments prior to field evaluations.
• Assessing mealybug microbial loads – is the mealybug carrying a pathogenic agent?
  • Initial investigation into the potential of the mealybug carrying and spreading a bacterial, fungal, virus, or other agent affecting pasture grasses.

Treatments evaluations

• Evaluating a number of potential control strategies, applicable to broadacre grazing, spot control with the goal of developing an IPM (integrated Pest Management) plan for mealybug in pasture grasses.
  • Natural enemies – reliant on life history and breeding project
    • Parasitoids – small wasps
    • Predators – ladybeetle and lacewings
• AVPMA emergency permits (early outbreak control)
  • Systemics
  • New chemicals – Following new research from CRDC in Cotton Mealybug
• Organic controls
  • Entomopathogenic Fungi – Fungi that attack mealybugs
  • Diatomaceous Earth
• New resistant grasses with tropical endophytes investigation
  • Initial discovery project into tropical grasses endophytes, which may lead to a range of resistance grasses species (long-term outcome).

Grass resistance – glasshouse and field trials

• Evaluation of a number of new species
  • A grass variety trial conducted earlier this year has highlighted a number of grasses that show promise as being less susceptible to mealybug attack. Some other grasses are being recommended by grass seed suppliers as potentials for natural mealybug resistance. All of these grasses are planned for laboratory trials to confirm mealybug resistance and, if successful, larger field trials later in the year.
• Legumes remain unaffected
  • Legumes are yet to be significantly affected by mealybug attack. Some evidence of death of legumes in the field have been observed but these have been as a result of other issues and not mealybug. There is an opportunity to build on this and increase the number of legumes planted in pasture along with other grasses, such as native grasses, to provide a more diverse and hopefully less susceptible pasture mix. Green house trials will precede field trials.
• Other stock feed types are being evaluated with insect resistance and provide safe fodder for cattle.
  • During the cooler months, crops such as brassica can be planted instead of traditional grasses. Brassicas have also been shown to release compounds or by-products that exhibit broad activity against bacteria, fungi, insects and weeds which may be beneficial against mealybug. A range of brassicas will be trialled in small plots initially to prove the concept.
  • Researchers are still working on ascertaining why the grasses in Leucaena rows (once affected by mealybug) die and don’t recover – or at least don’t return to their previous vigour. Some form of toxicity is being investigated, but results are yet to be received.

This update was prepared by pasture dieback research consultants in consultation with MLA.

For more information, contact:

pasturedieback@mla.com.au