News

Many theories, few answers in pasture dieback mystery

James Nason, 25/06/2018

 

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.

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Comments

  1. Ian Bell, 27/11/2021

    After 25 years managing pastures here in England without a single, solitary application of synthetic fertilisers, nor “cides” of any kind, I can say for sure that the cause of such disablement of pastures begins with the still accumulating folly of using synthetic NPK products. In countries where drought may be commonplace, severe, or both, such “fertilisers” (for they are not really so) become extremely dangerous. “Inorganic forces breed only inorganic substances”: So spake Justus Von Liebig, inventor of artificial NPK in the 1920s. Ironic, is it not, to consider that in these days of carbon-demonising, that carbon is the one very sadly depleted element in these agriculturally troubled areas. Starter evidence for this, (though there’s more to it of course) is the post-burning resurgence of grasses where “organic forces” (those of carbon) become available to some extent, once more. Pasture die-back is yet one more prompter from the essentially spiritual – yes, spiritual – world of Nature that material “science” has run its course; an abyss beckons. As bold a claim as it may seem, if enough interest is shown in my own solution to turn the tide on pasture dieback, then I’ll be happy to supply it.

  2. Albert Lowry, 10/11/2021

    In South Texas, USA, we have Buffel Grass Blight, a virus similar to Wheat Rust. There is a seed blend developed to reseed areas which are badly affected by the blight, Laredo Variety from Pogue Seed Company of Kenedy, TX.

    The virus was first noticed about 20 years ago and hits plants that have had good soil moisture , then expirience hot dry weather, with foggy mornings. The leaves turn red and the plant loses all vigor and mass. Standing forage can decrease by ~75%, if dry continues, the leaves just disintegrate to dust ! Most of the plants have very little viable seed production. The drought hardiness is no more,

    I noticed this year, the virus hit even native grasses, which were not affected before.

    We are seeing another anomaly in our Buffel Grass pastures, where an area of land will just end up being completely bare of growing plants, only having the root crowns of dead buffel grass remaining, can range from 1/2 acre to 10 acres. Very odd.

  3. KAREN Mary WEBB, 14/05/2019

    I appreciate the information and research provided so far on this pasture destroying issue, which is yet be diagnosed. My experience with this problem became evident from 2011 onwards (at that stage only small areas) and from then until now (huge areas) has spread to over three quarters of the area of the brigalow scrub component on the Branch Creek property.

    Because of the timeline in finding a cure, and the dead grass is underneath a cover of useless weeds, I have found it necessary to reduce the carrying capacity by half and monitoring regularly.

    On this property I have witnessed large areas of Green Panic with black/orange rust, Gayndah buffel grass with brown and red leaves and stems, Bisset blue grass with similar symptoms, and Black spear grass, which all will certainly eventually die. The only relationship between all these grasses dying is the timing.

    Another property (forest country) with Bisset blue grass has signs of die back only small areas dead yet, just waiting for it to die.

    It is imperative that an accurate diagnosis takes priority due to the seriousness and complex recovery processes which will need to be enacted immediately.

  4. Marie Vitelli, 27/06/2018

    Fungal pathogens of plants have spores that readily spread by prevailing wind currents. Heavy daily dew periods followed by breezy days are ideal for pathogen build up & spread. Look at other pathogen incidences in comparison such as grain crop diseases, myrtle rust on trees, rubber vine rust & Noogoora burr rust. Previous burning and/ or short cropped pasture has reduced prevalence of improved pasture dieback, in most cases. Perhaps pasture dieback will require revision of best practice grazing methods during high risk years of certain seasonal conditions.

  5. Jannie Baard, 26/06/2018

    I think the Queensland problem start with continued drought conditions. Looking at the symptoms it look like a typical potassium and or phosphorus deficiency. If it was calcium and or a magnesium deficiency I would say it could be a fungi problem but with potassium deficiency it’s more likely to be a bacterial problem.
    With potassium under 2% base saturation these diebacks are very likely. Most broadleaf weeds favour potassium deficient soils.
    It may even be a combination of a calcium, magnesium and potassium deficiency, because grasses favour calcium and magnesium over potassium.
    Mr Palmer do mention that grasses comes back after burning and in ashes are rich in potassium.
    The colour he is mentioning starting at the tips dying back towards the stem is also typical of potassium deficiency.

    Mr Palmer is 100% correct regarding his observation regarding the Mealybugs. The plants are under stress sending out a signal (vibration) for those bugs to attack and destroy them. That’s Nature’s way of cleaning up the dead.
    On the more fertile country more nutrients are getting removed through stock that favours the vegetation growing there.
    Mr Palmer also mention that it cuts on the fenceline of some paddocks. That’s because of different management between those paddocks.
    Were the grasses are shorter the requirement for potassium is less, that’s why there is less dieback.
    Satellite or NDVI images will help you to identify those spots where these dieback is most likely to occur.
    I was a biological farmer in RSA for a long time, but now I do consulting regarding biological farming.
    Kind regards Jannie

  6. Augusto Semmelroth, 25/06/2018

    The symptoms presented in the article sound remarkably similar to the widespread pasture dieback seen in Brazil over the last 15 years, particularly with Brachiaria Brizantha in “monoculture” paddocks. Embrapa (CSIRO-equivalent in Brazil) has done extensive research into mapping vulnerable areas and investigating the root cause of the dieback. Their key findings are the following: 1- Primary Cause: Temporary waterlog creates a lot of stress to some tropical grasses making them vulnerable to pathogens. 2- Secondary Cause: Some species exudate ethanol under waterlog stress, which in turn, attracts some specific pathogenic fungi (i.e. Rhizoctonia, Fusarium and Pythium) and also serves as “feed” to them. As a result, you start to see patches of diseased and dying plants across the paddock until it potentially takes over the whole area. Embrapa’s advice has been to switch to more water resistant grasses such as Brachiaria humudicula cv. Llanero, Brahiaria ruziziensis and other Panics and Cynodons. In other words, there’s not much you can do aside from changing to other grasses. The general context in Australia may be slightly different given the greater diversity of grass species in the same paddock and overall lower rainfall pattern. However, it would be interesting to see if the attacked areas have had any periods of temporary waterlogging and the incidence of the fungi species mentioned above. Their view is also that the fungi may have spread through roads and through the purchase of already infected grass seeds.

    Good morning Augusto, thank you for sharing these valuable insights from Brazil’s experience with dieback, which no doubt will be of interest to the research team investigating pasture dieback here. Augusto hails from a family cattle enterprise in Brazil and Paraguay but is well known to the Australian livestock industry, having completed a Master of Agribusiness at the University of Melbourne and worked as a livestock market analyst for Mecardo from 2012-2015. He is now a portfolio manager with Insight Investment in London, and a non-executive director of his family’s cattle operations in South America.

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