An integrated approach to effectively manage pulse diseases a South Australian perspective

An integrated approach to effectively manage pulse diseases a South Australian perspective

Take home messages

  • It is important to implement integrated disease management (IDM) strategies to reduce the threat of disease during 2025.
  • Where possible, choosing more resistant varieties will reduce grain yield losses caused by disease and reduce the reliance on fungicides.
  • Continue to adopt a 3- to 4-year rotation between crops of the same type to reduce inoculum build-up.
  • Timely fungicide applications are essential if conditions are conducive for disease development.
  • Following the ‘Fungicide Five’ strategies will reduce the risk of fungicide resistance development.

Year in review

Extended dry conditions across most cropping areas of South Australia in 2024 resulted in no substantial disease infection in pulse crops. Dry conditions also restricted crop growth and biomass production, and canopy closure was not achieved in many crops. Some minor Ascochyta blight lesions were observed early in lentil crops grown in tight rotations but did not spread to substantial levels due to the dry conditions.

Varietal resistance ratings

One of the first lines of disease defence is selecting varieties with genetic resistance. With large investments and substantial effort from pulse breeders and researchers, there is now a range of resistance categories available for many of our major pulse diseases. However, planting the same crop in close rotation and pathogen evolution can result in ratings changes or breakdown in resistance. At the time of article writing, the latest variety resistance ratings are not available and you are encouraged to view the latest ratings once available either through the National Variety Trials (NVT) website (https://nvt.grdc.com.au/nvt-disease-ratings) or when the 2025 Agriculture Victoria Pulse Disease Guide is released on Apple Books or the website (https://agriculture.vic.gov.au/biosecurity/plant-diseases/grain-pulses-and-cereal-diseases/pulse-disease-guide).

Sclerotinia white mould (SWM)

Sclerotinia white mould (SWM) poses an increasing threat in southern Australian grain-growing regions. It is a damaging disease that can infect all pulse crops including lentil, chickpea, faba bean, vetch, field pea and lupin. It can also affect canola, pasture legumes and many broadleaf weeds. This disease poses its greatest risk during seasons with prolonged damp conditions.

Sclerotinia white mould is caused by the soilborne fungi, Sclerotinia spp., and produces durable survival structures (sclerotia) that survive in the soil for many years, creating a legacy effect for future pulse or canola crops. High sclerotia populations can lead to basal stem infection and seedling death. Symptoms include bleaching or cottony white fungal growth on and in foliage, stems, pods and grain, and flowers. Sclerotia on/in plant foliage can contaminate harvested grain, acting as a future inoculum source if the grain is not screened. Refer to the Field Crops Diseases article ‘Sclerotinia in Victorian pulses' in the useful resources section below for images of symptoms.

Field experiments have been conducted in SA and NSW during 2023 and 2024, but dry spring conditions did not result in substantial SWM infection, highlighting the importance of environmental conditions in the development of SWM. Further highlighting the effect of season, NSW DPI experiments have shown season drives inoculum production (Table 1), with greater inoculum carry over following wet springs compared to dry springs. Management of SWM through fungicides has been highly variable on disease severity, grain yield and the subsequent inoculum levels in a paddock. The greatest driver of inoculum levels has been crop choice and spring rainfall (Table 1).

Table 1: Comparison of the weight of sclerotia produced by Sclerotinia sclerotiorum following infection of various pulse crop species grown at Wagga Wagga NSW.

Pulse cropSclerote weight produced/ha
2023 (dry sowing)2022 (wet spring)
Narrowleaf lupin7.0kg/ha48.8kg/ha
Faba bean108g/ha9.3kg/ha
Chickpea96.1g/ha– (not measured)
Lentil195g/ha3.2kg/ha

Management of SWM in pulses

Currently, crop rotation and careful paddock selection to avoid SWM infection are the most effective control measures. High risk paddocks are those with canola or pulses in the rotation, a history of previous outbreaks of SWM, and/or where high growing season rainfall is forecast. There are multiple hosts of SWM, including pasture and broadleaf weed species. PREDICTA®B testing of Sclerotinia spp. inoculum levels in soil after harvest can assist growers in determining disease risk. The behaviour of SWM in pulses is very different from that in canola and should be managed as such. For example, the plant-to-plant spread of the disease is unique to lentil. We are expecting the GRDC investment in SWM will provide more management options in the next few years.

Faba bean Ascochyta blight

Ascochyta blight in faba beans is often thought to be an important limitation. It can be controlled with good integrated disease management and agronomy including crop rotation, variety resistance, mixing and rotating fungicide groups, and strategic fungicide applications. Two experiments were conducted under irrigation in Victoria to determine the relationship between disease severity and grain yield in a susceptible variety. There was no correlation between disease severity and grain yield losses during 2022, even with a maximum disease severity of 20%. During 2023, a preliminary regression analysis showed a 1t/ha yield loss (from 5t/ha to 4t/ha) with 25% disease severity (P<0.05), compared to plants without disease. The maximum disease severities in both years were achieved with multiple inoculations through both stubble and spores, along with substantial irrigation. This highlights that, although Ascochyta blight on its own can cause yield loss, it is more likely to pose a greater threat in aiding Botrytis infection later in the season. This is likely as a result of providing dead bean leaf tissue which Botrytis can thrive on.

Botrytis disease management

Botrytis affects most pulse crops (faba bean, lentil, vetch, chickpea and lupin). The disease is called chocolate spot in faba bean and sometimes in vetch. It is caused by two pathogens, Botrytis cinerea and B. fabae which are both found across faba bean, lentil, vetch and lupin, with chickpea only affected by B. cinerea. Therefore, Botrytis can spread readily between susceptible pulse crops or from previously infected stubbles. The pathogens are necrotrophic fungi, which means they kill plant cells and then feed off those dead cells. This infection process places stress on the plant which makes plants more susceptible to further infection. Thus, it can become more difficult to control the disease once it is established resulting in greater disease severity.

The results from previous experiments reported in GRDC Update papers over the last few seasons support controlling Botrytis disease early in the season and minimising disease severity in the crop. An application of a dual mode of action fungicide at canopy closure should provide 1–2 months of protection, depending on environmental factors. This should protect the crop until spring when we should have a greater understanding of the future disease risk and can determine if further fungicide sprays are required. An investment (DJP2304-004RTX) into Botrytis grey mould led by Agriculture Victoria in collaboration with SARDI, FAR Australia, Trengove Consulting and NSW DPI will provide more IDM strategies and some recommendations on contributing environmental factors.

Chickpea Ascochyta blight

Chickpea Ascochyta blight is the greatest disease threat to chickpea production, with all current varieties rated moderately susceptible to susceptible. Previous Agriculture Victoria research has shown that there are differences in gross margin between fungicide strategies, but the threat of fungicide resistance highlights the importance of product rotation. Newer, dual active chemistries provide longer protection, but the traditional multisite chlorothalonil still provides protection, just with more applications.

Advanced breeding lines close to release show greater varietal resistance than current varieties and a new GRDC investment with Agriculture Victoria and NSW DPI is investigating sowing time and different fungicide strategies to determine if we can reduce the number of fungicide applications with this greater resistance.

Fungicide withholding periods

To protect pulses, there are several fungicides available, and these vary in efficacy and label use patterns. When selecting products, it is important to consider products within an IDM program, the potential of the disease-causing pathogen to develop fungicide resistance, and the overall crop profitability. Remember that withholding periods of these products differ and following label directions is essential to remain within the maximum residue limits (MRLs). Extensive testing has been undertaken to develop these limits and use patterns. Current registrations and labels can be found on the manufacturers’ websites or at the APVMA (Public Chemical Registration Information System Search - portal.apvma.gov.au).

Fungicide resistance

Resistance to fungicides is becoming an increasing threat to crops across Australia. Currently, there are no new detections of fungicide resistance in pulses within Australia. Samples have been collected and tested across the southern region, which suggests that a change in resistance is not occurring, but the threat is always present.

Pulse production is reliant on foliar fungicides and many crops have only single active fungicide products applied at multiple times throughout the season. Therefore, there is a high probability that we may observe fungicide resistance in the future if growers do not take preventative steps at present.

There are five strategies that growers can adopt to slow the development of resistance in pathogen populations and therefore, extend the longevity of the limited range of fungicides available.

  • Avoid susceptible crop varieties. Where possible, select the most resistant varieties suitable and/or avoid putting susceptible varieties in high-risk paddocks.
  • Rotate crops. Avoid planting crops back into their own stubble or adjacent to their own stubble.
  • Use non-chemical control methods to reduce disease pressure. Delaying sowing and early grazing are examples of strategies that can reduce disease pressure.
  • Spray only if necessary and apply strategically. Avoid prophylactic spraying and spray before the disease gets out of control.
  • Rotate and mix fungicides/modes of action. Use fungicide mixtures formulated with more than one mode of action, do not use the same active ingredient more than once within a season, and always adhere to label recommendations.

For more information on the management of fungicide resistance, consult the ‘Fungicide Resistance Management Guide’ available from www.afren.com.au

Conclusion

With unpredictable seasonal conditions each year, it is important to adopt an IDM strategy to reduce grain yield losses. This strategy should be planned early and incorporate varietal resistance, paddock rotations, reliable agronomy practices (sowing time, interrow sowing, and nutrition), mixing and rotating fungicide groups, and strategic fungicide applications. Without a solid strategy, grain yield losses of greater than 90% may be experienced, depending on the disease if conducive disease conditions occur.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the authors would like to thank them for their continued support. Appreciation is given to all the organisations listed above, their staff, and the growers and agronomists who have assisted with these research programs.

Useful resources

South Australian crop sowing guide (https://grdc.com.au/resources-and-publications/all-publications/nvt-crop-sowing-guides/sa-crop-sowing-guide)

SARDI crop watch newsletter (https://pir.sa.gov.au/research/publications/crop_watch)

Report local observations – email sardi.pulsepathology@sa.gov.au with details of your observations for pulse diseases

Diagnostic plant samples – send plant samples to SARDI Pulse Pathology Plant Diagnostics, Locked Bag 100, Glen Osmond, 5064. Send plants packed in paper with damp paper towel and post them at the beginning of the week so the parcel does not get held up in the post. Collection kits with return envelopes will be provided to growers and advisers willing to provide samples; please contact sardi.pulsepathology@sa.gov.au

Pulse disease guide (https://agriculture.vic.gov.au/biosecurity/plant-diseases/grain-pulses-and-cereal-diseases/pulse-disease-guide)

Sclerotinia in Victorian pulses (https://extensionaus.com.au/FieldCropDiseasesVic/sclerotinia-in-victorian-pulses/)

Crop protection product details, including Minor Use Permits, can be viewed at the Australian Pesticides and Veterinary Medicines Authority (APVMA) website (www.apvma.gov.au)

Contact details

Sarah Day
SARDI
70 Farrell Flat Road, Clare SA 5453
sarah.day@sa.gov.au
@Sarah_Day_

Joshua Fanning
Agriculture Victoria
110 Natimuk Road,  Horsham VIC 3400
0419 272 075
joshua.fanning@agriculture.vic.gov.au
@FanningJosh_

Date published

February 2025

GRDC Project Code: DEE2404-002RTX, UOA2105-013RTX, DEE2403-003SAX, DAW2112-002RTX, DJP2304-004RTX, CUR2403-003RTX, CUR2302-002RTX, DPI2206-023RTX, DEE2407-001RTX,