For more than a decade, graziers across Queensland have been baffled by a mystery murderer in their paddocks — watching helplessly as their lush green pastures turned yellow and died without explanation.
With a crime scene between 40,000 and 4.4 million hectares in size, researchers struggled to identify the culprit, responsible for at least $2 billion in lost productivity.
But they have finally caught a break in the case, and the suspect is four times smaller than a five cent piece.
And now, farmers like Chris Roffey hope a new trial investigating best management practices means they can move on, control it and recover.
The crime
The first signs of a problem in Queensland's pastures was discovered in 2011 in the state's north, and since then it has spread through central and southern areas and into northern New South Wales.
On Mr Roffey's property at Gaeta, about 100 kilometres west of Bundaberg, he and his two brothers first noticed pasture dieback in 2016.
It has become a constant management challenge.
"Wherever it's really bad we go back through and we replant the seeds, so it's money and time," he said.
"You don't really want to spend time doing that — [you have] other things to do."
Gympie's Ivan Naggs used to take pride in his "great pasture," but the dieback has devastated his property.
He has reduced his breeding cattle by one-third due to lack of feed, and as a small stud it has been a significant loss.
Mr Naggs is a member of the Meat and Livestock Association's (MLA) oversight committee working to tackle pasture dieback.
The committee estimates the economic hit to productivity because farmers cannot use their paddocks exceeds $2 billion.
The investigation
Just five years ago researchers still had no clue what was killing Queensland's grasses.
At a field day in 2018, graziers were told everything from the weather to insects, nutrition, microbes, viruses, DNA, and chemicals were being investigated to provide answers.
The state government, universities and the industry teamed up in a joint investigation dedicated to uncovering the culprit.
Queensland University of Technology microbiologist Caroline Hauxwell was part of the squad.
"I don't know how much more seriously it could be taken but it's very serious," she said.
While examining the fast-spreading problem, the researchers started to notice a small, easy-to-miss presence wherever they found dieback — mealybugs.
The culprit
Mealybugs, or heliococcus summervillei, are sap-sucking pests that feast on pastures.
When the weather is warm and grasses are green they feed on the leaves, and when the weather cools down the adult population hunkers down to wait out the cold.
The females produce their young during the winter and immature mealybugs cause widespread damage the following spring.
This breeding cycle goes some way to explaining how dieback can seem dormant, then in just a few months run rampant.
The bugs are small — between 3 and 7 millimetres.
But Dr Hauxwell said the tiny creatures posed a "massive biosecurity threat" for graziers.
"You've got to look," she said.
"Look for these mealybugs, learn what to look for, what the symptoms are, what [they] actually look like.
"Start to think about how you manage mealybugs, because that's the key to it."
The trial
Back at the Roffey's farm near Bundaberg, about 30 to 40 per cent of the property is crawling with mealybugs.
"[Some areas are] absolutely stone motherless dead through to just affected," Mr Roffey said.
While frustrated, he hopes finally having an answer meant new management systems — like planting feedstock resistant to the bugs — can help improve his land.
"We're probably looking for a new pasture or new pastures, particularly grass," he said.
"We're pretty well set up for legumes, but we are also trying desmanthus."
The lead researcher of Applied Horticultural Research's pasture dieback trials, Naomi Diplock, has been working at Mr Roffey's property for two years investigating best management practices.
Her four trial sites have found re-sowing land with legumes and mixing grasses have been the most successful methods for controlling mealybugs.
But graziers have to act fast — at the first sign of the grass turning a yellow-purple colour.
Other forms of management have also been somewhat successful, including spring grazing, bailing during the summer months, slashing, and planting foraging crops.
Grazier Ivan Naggs believes eradication is not an option and the problem will instead will require long-term management.
"I believe it's here to stay," he said.
But he says the cost goes far beyond the losses reported.
"I still stick with my assumption that the mealybug in Queensland is costing graziers between $3-4 billion in lost productivity," he said.
