Pasture dieback

Pasture dieback was confirmed for the first time in NSW on flood plain/flat country in 2024, starting in couch grass then moving to other grasses such as kikuyu or paspalum. Prior to this, dieback had only been seen on undulating to steep hill country in NSW.

Pasture dieback has continued to spread along the NSW North Coast in a southerly direction since first being detected near Murwillumbah in Autumn 2020. Between January and June 2024, new infections were confirmed around Grafton and Coffs Harbour regions. There has also been continuing cases of new infections within parts of the Tweed, Byron, Ballina, Lismore, Casino, Tabulam and Kyogle shires.

The following map of northern NSW and Queensland shows areas pasture dieback is known to be present (bright green), as of June 2024. (Source: DAF QLD).

Observing changes in the pasture over time helps to differentiate pasture dieback from other disorders. Be on the lookout for the following symptoms of pasture dieback.

• Yellowing, reddening and purpling of leaves. Discolouration can vary between species. 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.
• Starts as small patches, less than 1m². Patches grow and merge and affect large areas.
• Rapid increase in size of the infected area following significant rainfall in spring-autumn.
• Eventually the affected plants die.
• Patches where grasses have been killed are colonised by broadleaf weeds and legumes.

Above: Broadleaf paspalum leaf discolouration.	Initial Symptoms: The earliest signs of pasture dieback include leaf discolouration, which manifests as reddening, purpling, and/or yellowing. Affected grasses exhibit unthrifty growth.
Above: Patches of dieback spreading across paddocks.	Progression: The disease starts in patches but can quickly spread to cover large areas or entire paddocks within a single growing season.
Above: Broadleaf weeds colonising a dieback affected area	Aftermath: Once the grasses die, the affected areas are often colonized by legumes and/or broadleaf weeds.

Many of the dieback plant symptoms can be caused by a range of other factors. Including: mineral deficiency, moisture stress, cold temperatures, herbicide damage, water logging and nematodes. It is important to eliminate these before assuming dieback. However a combination of symptoms, including a rapid increase of the affected area following significant rainfall are good indicators of pasture dieback.

• Highly susceptible grass species. Some grasses are more susceptible than others
• High biomass
• Active grass growth
• Hot/humid weather
• Nutrient stress
• Secondary plant infections (viral, fungal or bacterial).
   

If considering improving the pasture composition always select species that are well suited to your soil type, enterprise objectives and grazing management practices to ensure on going persistence.

Revisit the advice above on:

• More susceptible grasses
• More tolerant grasses

Abovet: Setaria (a less suceptible grass) over-sown with Haifa white clover.

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

Reducing cattle numbers is likely to be necessary if no steps are taken to maintain feed supply. Even then reducing numbers may prove the best economic decision as long-term hand feeding is seldom viable.

It will very likely mean thinking outside the ‘normal’ way things have been done.  Reconsidering grazing strategies such as stocking rate, grazing time, and prioritising livestock classes can be challenging and confronting in the initial stages. Some producers have sought long term leases elsewhere to maintain breeders and currently grow annual forage crops in the dieback affected country for growing weaners out or for hay and silage conservation.

Others have chosen to move from a breeding to a trading operation which can offer more flexibility to adapt to changes in feed availability.

The decision to significantly change the grazing operation of a farming business (e.g., from breeding to trading) requires detailed thought, thorough gross margin and cashflow budgeting, along with a realistic assessment of all farm and business resources. Consider seeking advice before making these big decisions.

There is no one size fits all approach to managing pasture dieback. This is because every farm and farm system are different, and has different resources (labour, time, money, soil, pasture, arability, rainfall etc). In some cases, minimal intervention can be the right approach, especially if pasture regeneration is likely to naturally occur from the seed bank or runners from unaffected plants, without colonisation from unwanted or noxious weeds.

However, ‘doing nothing’ will still mean reducing livestock numbers, fodder budgeting, and spraying broadleaf weeds if the general condition of the farm is to be maintained. In affect minimal intervention is better termed as Managing for Recovery.

Manage for recovery (infographic)

Image shows arrows connecting these strategies: Manage for recovery, Control pasture mealybug, Improve pasture, Sow a break crop. Land managers can choose one or multiple strategies to suit their situation. For example, a paddock may be sown to a break crop, then planted to an improved pasture with legumes and tolerant grasses. (Source: DAF QLD)

In QLD, the Department of Agriculture and Fisheries (DAF) and other research organisations in collaboration with Meat and Livestock Australia (MLA) have investigated management options for pasture dieback since 2018. In NSW since 2022, North Coast Local Land Services (LLS) and Southern Cross University have been investigating management options based on the QLD trial work to determine what suits our conditions on the north coast. Trials are continuing in NSW to gain a longer term understanding in our environment.

Results from trials on commercial properties, along with experience assisting graziers over several years have been used to develop four management strategies for pasture dieback.

Management strategies for pasture dieback affected country based on the size and type of affected area. (Source: DAF QLD)

✓ Suitable                              

x Unsuitable                         

? Provides inconsistent results

Some pastures can recover from dieback and grasses will re-establish from the soil seedbank or runners from unaffected plants. How long recovery takes and how well the grasses return depends on seasonal conditions, and the management undertaken to aid recovery. Fodder budgeting and adjusting stocking rate accordingly is important to maintain stock condition and to enable pastures to regenerate and establish without excessive grazing pressure. It is also important that these pastures are allowed to set seed to ensure the soil seed bank is replenished.

Weed control is essential in NSW coastal conditions following pasture dieback. Weeds can out compete recovering grasses, so as a minimum, control of broadleaf weeds is essential to help speed up recovery times. Where broadleaf weeds have been left untreated, excessive competition has resulted and any grasses trying to germinate and re-establish are faced with extreme competition preventing rapid growth and ability to form a dense pasture. If you are unsure about options for chemical weed control, seek advice on suitable products given your plans for the paddock.

Many of the chemicals commonly used on the north coast can have residual effects and plant-back periods. This means some fodder crops, legumes and even some grasses, can’t be sown until a certain amount of time has passed. Not abiding by these recommendations will result in poor or no establishment.

Some paddocks have recovered within 18 months with good weed control and grazing management. Other paddocks where weed control and grazing management were not implemented have taken over 3 years to recover. While weed control has a cost, fodder budgeting and grazing management decisions have a minimal cost, the highest cost is the lost productivity over many years of slow or poor recovery.

Above: Kikuyu pasture regenerating after dieback showing the impact of no weed control and no fertiliser (left hand side photo) vs weed control + fertiliser (right hand side photo)

Pasture improvement is a highly effective way to return to productivity after being impacted by pasture dieback. This includes sowing perennial legumes, herbs and tolerant grasses, fertilising, renovating via cultivation, or a combination of these.

In the NSW north coast region, we are fortunate to have many tropical and temperate legume and herb options to consider. From a pasture dieback recovery perspective, legumes and/or herbs should seriously be considered for inclusion as they are not susceptible to pasture dieback.

However, their successful establishment and persistence will require good management. In some instances, existing pastures dominated by grasses can have legumes and herbs over-sown with reasonable success if careful management is undertaken. The level of success will depend on the suitability of the legume and/or herb chosen for the soil type, the time of year and sowing method used, management of the existing grass and broadleaf weeds present, and the subsequent grazing practices. Taking short cuts seldom works. Simply throwing some legume seed into a healthy summer grass stand, slashing it, and then shutting the gate is unlikely to work. Seek advice on your specific situation.

Above: Glycine, siratro and setaria were broadcast immediately following dieback in a creeping bluegrass pasture west of Casino with great success. This resulted in a return to good pasture production in less than 18 months. The owner undertook, weed control via spot spraying, and intense heavy grazing based on forage budgets to assist in paddock preparation. Seed was broadcast due to terrain and tree density.

Cultivation can break a pathogen cycle and accelerate nutrient cycling, providing a healthier, nutrient-rich environment for new seedlings to thrive in, but it can also result in a high germination of weed species if miss timed, or the existing seed bank of desirable species is depleted. Best results on the north coast typically result from cultivation being used as part of a re-sowing program. Some soil disturbance has also provided reasonable results in old (>15-20yo) Rhodes grass and setaria dominated pastures. This was most likely due to a large soil seed bank reserve and stimulation of nutrient cycling after many years of no disturbance.

Conducting soil tests and applying fertiliser and/or soil ameliorants such as lime and gypsum will help supply nutrients to maximise the new or recovering pasture’s productivity and persistence, provided the grazing is well managed. In many situations phosphorus (P) and/or sulphur (S) will be required and are vital for good growth of legumes and herbs. Nitrogen (N) will also assist grass and herb growth, but excessively high rates (e.g. >60kg N/ha/month) can be detrimental in a couple of ways, firstly rapid grass growth can lead to more competition against legumes if not managed, and secondly, in some instances high rates of nitrogen has resulted in increased mealybug activity in susceptible species. Options like chicken manure are also valuable sources of nutrients in some soils. There can be considerable variations in the level of nutrients between loads of chicken manure depending on where it is from, request a nutrient report so you know what rate to apply it at.

Above: Successful establishment of white and red clover directly into dieback affected country following weed control, soil testing and application of adequate phosphorus and sulphur fertiliser to assist legume establishment. No grasses were sown in this instance as the intention was to establish legumes and see if the existing Rhodes grass and creeping bluegrass would regenerate.

A break crop, such as an annual forage (or grain crop), can be used in arable soils to break a disease cycle and generate short-term feed supply. A forage crop could be grazed, baled or used for silage, depending on the feed requirements and the machinery available. The intention is to sow a break crop for one or two years, then return the paddock to a perennial pasture which includes legumes and tolerant grasses.

Pasture dieback doesn’t affect annual temperate species. In arable paddocks with suitable soil types, ryegrass, oats, wheat, barley, and triticale all grow very well through winter. Pasture dieback also doesn’t affect summer growing forages including millet, sorghum, and teff grass (a summer annual grass), and summer legume crops such as soybeans, cowpeas and lab lab. Sowing forage crops has created situations where productivity has increased through a higher quality feed base on offer.

Poor weed control and/or low fertility soils without fertiliser use will lead to disappointing annual forage and animal productivity results, leading to poor economic returns. Therefore, understanding limitations of the paddocks, soil, diseases, other pests such as Fall Army Worm (FAW), access to machinery and budgets are a must before taking this approach.  Seek advice from your local agronomist.

Above:  Cows grazing millet near Coraki that was direct drilled into a paddock that had couch, kikuyu and paspalum severely impacted by dieback late 2023. Photo taken early February 2024.

Currently there are no chemicals registered in NSW to control the pasture mealybug. Some chemicals were previously available on a permit basis however these have expired and have not been renewed at the date of writing. Check the APVMA Permit data base for any updates. The fact sheet; Pasture mealybug and its role in pasture dieback contains more detailed information on pasture mealybug and the challenges associated with controlling them.

Chemical options have significant limitations for effective control of pasture dieback in commercial operations for several reasons:

1. The timing of chemical application during the life cycle of the pasture mealybug is important, but difficult to achieve, as there can be multiple life stages of mealybugs present at the same time in pastures from adults to juveniles. Juveniles’ stages can be very hard to see in the pasture and they are also spread on the wind, which makes it difficult to know where to look next for them.
2. The terrain and size of paddocks means some areas are inaccessible to spray rigs, drones, planes or helicopters.
3. Registered chemicals have historically been very expensive and most chemicals that have been registered to kill pasture mealybug also kill the beneficial insects that prey on them,
4. Many of these chemicals can have specific and long withholding periods (WHP) that affect when pastures can be grazed after application.

So, at this stage targeting mealybugs chemically is not recommended as it is unlikely to provide effective pasture mealybug control, be cost effective, nor be practical long term at a commercial grazing scale.

In areas with small patches of dieback where:

1. the pasture mealybug can easily be identified
2. spray equipment can access
3. cattle can be excluded from the area; chemical application can be an option if funds allow.

In NSW, under Section 57 of the NSW Pesticides Regulation 2017, you can legally apply a chemical registered in a pasture (or crop) to a pest (weed, insect, disease) that is not listed on label. This use pattern must not exceed the maximum label rate for the chosen product within the said crop, in this case pastures. Seeking advice from a reputable agronomist is recommended.

But in deciding to spray patches you need to be realistic in your efforts. Whilst some benefit may be seen in the sprayed areas, the effect is short term and it does not guarantee that mealybugs and dieback will not occur elsewhere in the paddock or on the farm a few or several hundred meters from where you sprayed.

Queensland trials showed, burning has only provided very limited benefit, however, several producers in QLD and NSW have anecdotally reported that mosaic burning has provided temporary benefit. So, it remains unclear how beneficial burning is as a management strategy. Potentially the timing of the burn relative to the level of dieback and tolerance of the species present will have the biggest influence on the level of success.

Typically, the dead material may burn and potentially some surface mealybugs are killed. Following rain an initial grass growth response is seen but rarely do these green shoots establish enough to form a dense grass pasture. It is likely that some mealybugs will have remained underground and can rapidly restore populations. 

This information has been developed for NSW coastal conditions and is based on the original “Management of pasture dieback” fact sheet developed by DAF Queensland. Some sections have been modified and additional information added where appropriate to align with the unique NSW far north coast environmental conditions and grazing system.

Kylie Hopkins and Stuart Buck, DAF Rockhampton, and others within the wider QLD DAF Pasture Resilience team contributed to the original fact sheet on which this advice is based.

Dr Suz Boshma, and Sarah Baker, NSW DPI, contributed to the review of this information.

• APVMA Chemical Permit Database: - APVMA; Agricultural and Veterinary Permits Search - portal.apvma.gov.au
• Best practice guidelines for poultry litter on pastures – NSW DPI; Best practice guidelines for using poultry litter on pastures (nsw.gov.au)
• Collecting and Submitting soil samples – NSW DPI; Collecting and submitting soil samples (nsw.gov.au)
• Controlling pasture mealybugs in grass pastures; NSW DPI –
• Eight steps to successful perennial pasture establishment – NSW DPI; Eight steps to successful perennial pasture establishment (nsw.gov.au)
• Establishing and managing chicory and ryegrass pastures on the NSW north coast – NCLLS; https://www.lls.nsw.gov.au/__data/assets/pdf_file/0005/1299137/Establishing-Chicory-Fact-Sheet-March21-V1.pdf
• Forage & Fodder crops – NSW DPI; Forage and fodder crops (nsw.gov.au)
• Forage Sorghum & Millet- NSW DPI; Forage sorghum and millet (nsw.gov.au)
• How do I select grass varieties tolerant to pasture dieback – MLA; select-grass-varieties-factsheet-final-approved.pdf (mla.com.au)
• Management of pasture dieback – DAF; Management of pasture dieback brochure (futurebeef.com.au)    
• NSW weed control handbook – A guide to weed control in non-crop situations- NSW DPI;  New South Wales Weed Control Handbook, Seventh Edition (nsw.gov.au)
• NSW Pesticides Regulation 2017; NSW Legislation - Pesticides Regulation 2017 - NSW Legislation
• NSW Winter crop variety sowing guide – NSW DPI; NSW Winter crop variety sowing guide
• Tropical Perennial grasses grazing management – NSW DPI; Tropical perennial grasses – grazing management (nsw.gov.au)
• Summer Legume Forage crops: Soybeans, Cowpeas and Lab Lab; NSW DPI - Summer legume forage crops: cowpeas, lablab, soybeans (nsw.gov.au)