Pasture dieback

Pasture dieback is a condition that causes the premature death of high-yielding tropical and sub-tropical grasses. Learn how to identify, prevent and respond to pasture dieback. This is part of your biosecurity duty as a landholder in NSW. 

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At a glance...

Pasture dieback primarily affects landholders in north-eastern NSW and can have significant impacts on pasture productivity and farm management, including:

  • loss of productive pasture, with sown and native summer growing pastures dying off
  • the spread of small outbreaks into larger effected areas  
  • declining groundcover, as dying grasses allow broadleaf weeds to colonise
  • less productive livestock as they avoid grazing affected areas
  • increased vulnerability of improved pastures, with sown grass commonly impacted and some native and naturalised species also affected.
On this page

Local Land Services works with landholders to help identify and respond to pasture dieback. Our staff can assist you to recognise this in pastures, rule out causes of decline and provide advice on pasture management.

Landholders who suspect pasture dieback are encouraged to contact their Local Land Services office for support.

How to identify pasture dieback

Susceptible grass species with a large amount of biomass, favourable environmental conditions (warm and wet), and the presence of the pasture mealybug can contribute to pasture dieback. 

Observing changes in pasture over time helps to differentiate pasture dieback from other disorders. Look for the following symptoms:

  • yellowing, reddening and purpling of leaves. Discolouration can vary between species. It starts with the oldest leaves and typically begins at the leaf tip and moves along the leaf blade towards the stem
  • stunted and unthrifty growth. Plants have fewer leaves and tillers, smaller seed heads and a smaller root system
  • initial small patches, (less than 1m2) that grow and merge, affecting larger areas
  • rapid increase in size of the infected area following significant rainfall in spring to autumn
  • patches where grasses have been killed are colonised by broadleaf weeds and legumes.

Recognising symptoms

3:47

Recognising Pasture Dieback with Sarah Baker

NSW Department of Primary Industries Pasture Systems Development Officer, Sarah Baker, explains how to recognise Pasture Dieback. This video was produced by Granite Borders Landcare with funding from Northern Tablelands Local Land Services.

Read transcript
Video transcript

Recognising Pasture Dieback with Sarah Baker

Pasture dieback is a condition that's killing summer-growing pasture grasses. These are what we might call our subtropical, tropical, or C4 grass species.

So, what does pasture dieback look like? The first signs are leaf discoloration. Discoloration varies by species—some show yellowing of the leaf tips, others may appear red or orange, and some even display a reddish-purple discoloration. There are many things that can cause leaf discoloration, so it's worth ruling out other likely causes before assuming dieback.

From discoloration to plant death usually occurs within a growing season, so we're talking months rather than years. It starts off in patches, and those patches get bigger, particularly following significant rainfall events during spring, summer, and autumn when these grasses are actively growing. This is when we see the biggest increase in the size of affected areas. We're also seeing weeds colonize areas that have been affected and killed by pasture dieback.

Dieback only affects summer-growing grass species. Legumes are unaffected, as are broadleaf species, brassicas, and herbs such as chicory and plantain. These might be some options to sow into dieback-affected areas because we know they are not impacted by pasture dieback.

Pasture dieback was first seen back in the 1990s in buffalo pastures in central Queensland, and it was quite a problem at that time. But it wasn't until 2015 that we really started seeing the condition affect other grass species and spread. Now, it's been identified as far north as the Atherton Tablelands in Queensland and as far south as the Tweed Valley in northern New South Wales. Since then, the condition has moved further west into the hinterland and further down the coast.

There has been quite a lot of research done, particularly in Queensland, into what is causing pasture dieback. To date, there's been no clear answer, which highlights the complexity of the condition. It's likely there is an environmental component—whether that's drought, significant rainfall events, temperature, or poor soil fertility—and probably a pathogen component as well, such as bacteria, viruses, fungi, or insects.

What we don't know about mealybug is whether it is the causal agent for pasture dieback or whether plants are stressed because of environmental conditions and the mealybug just comes along as the final factor that causes the grass to collapse.

Grasses showing symptoms of pasture dieback are often unpalatable to livestock, so they are poorly utilized. As dieback patches grow and the area of dead grasses expands, there can be significant loss in productivity for producers and reduced carrying capacity for properties.

We're asking people to be on the lookout for pasture dieback. If they suspect it, they should contact NSW DPI or Local Land Services. This helps us track the spread of the condition so we can learn more about it and hopefully target our research more effectively.

Many pasture dieback plant symptoms can be caused by a range of other factors including mineral deficiencies, moisture stress, cold temperatures, herbicide damage, water logging and nematodes. It is important to rule out these causes before diagnosing pasture dieback. 

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Pasture mealybugs and yellow leaf discolouration of affected Rhodes grass. 

After ruling out other causes, a combination of other symptoms, particularly a rapid increase of the affected area following significant rainfall is a good indicator of pasture dieback.  

Symptoms are most evident when pastures are actively growing during spring, summer and autumn.

Identifying pasture dieback progression

Initial symptoms

The earliest signs of pasture dieback include leaf discolouration. This can be seen as reddening, purpling, and/or yellowing. Affected grasses exhibit unthrifty growth.

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Broadleaf paspalum leaf discolouration.

Pasture dieback progression

Pasture dieback starts in patches but can quickly spread to cover large areas or entire paddocks within a single growing season.

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Patches of dieback spreading across paddocks.

Aftermath

Once the grasses die, the affected areas are often colonized by legumes and/or broadleaf weeds.

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Broadleaf paspalum leaf discolouration caused by pasture dieback.

Causes of pasture dieback

Research has confirmed that the pasture mealybug (Heliococcus summervillei) is a microorganism that causes pasture dieback.

However, environmental conditions (water, temperature, and nutrient stress) and pasture management practices (species present, grazing strategy) can also contribute to the prevalence and severity of the condition. 

There are certain characteristics that make some pastures more susceptible to pasture dieback than others. These include:

  • highly susceptible grass species
  • high biomass
  • active grass growth
  • hot, humid weather
  • nutrient stress
  • secondary plant infections (viral, fungal or bacterial). 

Manage and learn more about pasture dieback

Managing pasture dieback

Find more information about identifying, managing and reporting pasture dieback.

Upcoming events

Find events from Local Land Services about identifying and managing pasture dieback.

Related information

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