Buffel grass pasture affected b dieback. Note the dead patch (left of photo) surrounded by well-grown buffel grass without any other grass species. Image: FutureBeef

A MYSTERIOUS condition is killing pastures across large and growing tracts of Queensland’s most productive cattle country, from the State’s far north to its southern border with New South Wales and now as far west as Roma.

The problem is at its most devastating in some of the state’s most productive grassland throughout the Central Highlands and Dawson and Callide Valleys and Burnett regions

There are many theories as to the possible cause but few actual answers.

Pasture Dieback is not a new phenomenon, having been first reported in buffel grass pastures near Moura in the Dawson Valley in the early 1990s.

However, its prevalence has rapidly accelerated in recent years.

A recent survey by MLA showed that of dozens of affected cattle properties, on average about 60pc of each survey respondent’s property was impacted by pasture dieback.

Pastures affected are “pretty much every tropical grass or subtropical grass you could name”, QDAF pasture agronomist Stuart Buck told the AgForce organised ‘My Produce, Your Plate, Our Future’ at Gayndah last week.

Impacted species so far included buffel, creeping blue grass, paspalums, brachiarias, setarias, digitarias, Rhodes grasses, and panics.

Native pastures also seem to be vulnerable, such as black spear grass and forest blue grass, but not as commonly as introduced varieties.

Adding to the mystery is that the same symptoms are rarely seen on the same place, and species that may be affected on some properties are not affected on others.

It has been found in a range of soil types and environmental conditions, and researchers have not found any obvious links between dieback and pasture nutrition.
After more than 12 months of active investigation researchers concede they are still in the dark as to the cause, and whether it is a fungus, a virus, a bacteria, an insect, soil nutrients or something else at work.

Greg Palmer, the consultant heading an MLA project investigating the problem, said if he had to identify a cause right now now he would lean toward a fungus spread by road transport.

“If anyone has driven around here, you will see it up all the roads around Queensland.

“In fact we believe the roads are a vector for spreading.

“If we had to pick something right now we would pick a fungus.

“We believe it is the action of trucks and b-doubles and b-triples that fly down the roads and if you look at them as they go past you can see the impact of the air movement from those vehicles 10-12 metres out from the road.

“So, if it is a fungus – and I say if because we don’t know – if it is sporulating and a b-double goes past, it will just suck those spores down the road.

“And it may sit there and wait until conditions are right for it to multiply and spread.

“Now we can’t prove that is the case.”

Symptoms and impacts observed so far include:

• Initial symptoms of pasture dieback are a vivid reddening or yellowing of the leaves, typically starting with oldest leaves first then the next oldest
• Colouration starts at the tip of the leaf and moves toward the stem of the plant
• Plants tend to die in circular patches, ranging from less than 1 metre in diameter to entire paddocks
• Once the pasture dies, patches tend to be colonised by other broadleaf plants including weeds and legumes. (Mr Buck said one of the first things graziers notice is a patch of weeds where they didn’t exist previously)
• Symptoms are more evident at the start of the growing or wet season when there is green grass and dead patches stand out
• It is not uncommon to see a fenceline affect, with grass on one side of a fence affected but not on the other side
• Observations suggest it is often the better, more fertile country types where dieback is worst
• However, there appears to be no obvious geographical or topographical pattern to where dieback is, appearing on tops and bottoms of hills and in gullies: “it is all over the place randomly”
• The loss of groundcover also presents erosion risks, particularly on sloping country.
• Where grass is kept shorter, generally there seems to be less or no dieback – but these are general statements and this does not occur in every case, Mr Buck said.
• Where there have been recent fires there has been less or no dieback
• Bigger spreads of dieback occur after torrential rain that is sufficient for soil to become saturated

Extensive surveys have been done, countless plant and soil samples have been analysed, and trial plots have been grown and infected with various potential pathogens, but the cause remains elusive.

Researchers say more extensive diagnostic work, replicated research trials and investigations of potential management intervention strategies, such as burning, slashing, grazing management, fungicide applications and cultivation, are now needed.

“It is a highly complex issue, and it will take some time to solve,” Mr Buck said.

Mr Palmer said he had seen pictures of grass that was sick or dead 8 months ago, but now a lot of that grass had come back in 90-95pc of those areas.

“That is interesting, we don’t know why,” he said.

Mr Palmer said a coinciding recent outbreak of mealybugs, the largest in scale since the 1920s, had also been identified as a potential vector for disease transmission.

However this was unlikely, he said.

“A lot of people out there think mealy bugs are the root cause, we don’t believe that is the case, we believe mealy bugs are an opportunistic secondary infection that come in when the plant is weak and there is something going on in the movement of the fluids in the plant that are making it attractive for mealy bugs to come and have a go at it.”

Mr Palmer said satellite mapping was also being undertaking to monitor where the problem is starting and spreading.

He said some fungicide trials have also been conducted which he said “look promising”, but did not elaborate further.

He said he believed the solution could come down to small changes “to push the pendulum back in favour of the plant and not the pathogens”.

Mr Buck said DAF has just started a scientific research investigation into dieback at Brian Pastures research facility, and plans to start another at Spyglass this coming summer.  The investigations will be aiming to diagnose the cause or causes of dieback, and to assess the impact of a range of management solutions.