An integrated approach to effectively manage pulse diseases

Take home messages

• It is important to implement integrated disease management (IDM) strategies to reduce the threat of disease during 2024.
• Where possible, choosing more resistant varieties will reduce grain yield losses caused by disease and reduce the reliance on fungicides.
• 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

During 2023, integrated disease management was key for profitable pulse production. There was early severe Ascochyta blight in lentils in many areas, with stem breakages and early plant death. This was usually associated with tight lentil rotations and high disease inoculum loads from the 2022 season. Early fungicide control mitigated this issue and the drier spring, in most areas, meant many diseases did not pose major issues for most areas of Victoria. Later observations in lentils through structured surveys did not identify Ascochyta blight. All lentil paddocks surveyed had Botrytis grey mould but with low disease severity. In faba bean paddock surveys, all paddocks had Cercospora leaf spot in the Wimmera and Western district regions of Victoria, with a maximum severity of 20% and 15% observed respectively. Chocolate spot was present in 100% and 80% of paddocks surveyed in the Wimmera and Western district regions of Victoria, with a maximum severity of 30% and 15% observed respectively. Ascochyta blight was not observed in any faba bean paddocks surveyed in Victoria in 2023. Overall, 2023 was not of considerable importance regarding disease prevalence in pulse crops in most of Victoria.

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 are susceptible. 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.

With increasing occurrences of SWM across Australia, the GRDC has invested in a national research project (DPI2206-023RTX). Surveillance in this project showed that 60% of paddocks across the Wimmera and Mallee had SWM present during 2022, but it was not detected during 2023, likely due to a dry spring.

Field experiments have been conducted in SA and NSW during 2023, but dry spring conditions did not result in significant SWM infection, highlighting the importance of environmental conditions in the development of SWM. During 2022, in Wagga Wagga, NSW, a lentil variety trial was conducted to assess yield loss from SWM and a moderate to high level of SWM developed. In comparison to the dry 2023, continued wet weather compromised 2022 results. Grain yields were highest in the complete control (fortnightly fungicide) treatment, but this was not always significant and the grain yield response to a single foliar fungicide application at canopy closure did not significantly increase yields over the untreated control (Table 1). Plant infection was lowest in the complete control treatment, but there were no significant differences between the untreated control and a single canopy closure fungicide application of Bixafen + Prothioconazole, (600ml/ha, Aviator® XPro® Table 1). Note, Aviator Xpro is not registered for the control of SWM in lentils. Interestingly, total sclerotia weight was highest in the complete control treatment (Table 1). This high sclerotia weight creates a disease carryover risk for future seasons.

Table 1. Effect of foliar fungicide treatment to manage Sclerotinia white mould disease on grain yield, infection percentage and sclerotia weight, averaged across five lentil varieties sown at Wagga Wagga, NSW during 2022. Note, Bixafen + Prothioconazole (Aviator Xpro) is not registered for the control of SWM in lentils.

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 Sclerotinia, and where high growing season rainfall is forecast. Note that 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.

Soilborne diseases

With the increase in pulses cropped in Victoria, a growing presence of soilborne disease has been observed. A rise in recent grower reports of poor performance has indicated that root diseases are common in Australian pulse crops and may be a major limitation to production. Whilst information on the potential impacts of root diseases affecting yield and biomass is unknown, the Australian pulse industry needs such information to avoid major production losses and potential loss of export markets. To target this issue, GRDC has invested in a national project (UOA2206-007RTX) that builds upon previous research (SAGIT S218 and GRDC DJP1907-002RMX) and focuses on providing new knowledge of the impact of key soilborne pathogens on pulse crops across the southern and northern GRDC regions. As part of this research, pathogens such as Fusarium sp., Phytophthoraand Rhizoctonia are being assessed in field and glasshouse environments to quantify their impact on pulse root health, biomass production, and yield. Preliminary results will be presented at the updates.

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, the disease 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. Therefore, it becomes more difficult to control the disease once it is established and can cause 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. A new investment (DJP2304-004RTX) into Botrytis grey mould led by Agriculture Victoria will provide more IDM strategies and some recommendations on contributing environmental factors.

Chickpea Ascochyta

To improve knowledge and management of chickpea Ascochyta blight, a multi-organisational approach across several investments occurred. These organisations included Agriculture Victoria, South Australian Research and Development Institute (SARDI), Griffith University, Curtin University, International Center for Agricultural Research in the Dry Areas (ICARDA), and the CSIRO. The following are the main outcomes of this collaboration.

• The majority of disease inoculum decays over 12 months, but inoculum is still present at low levels for at least 4 years. This means good IDM is required to reduce disease severity.
• Disease isolates are overcoming resistance sources in crops and the frequency of aggressive isolates detected across Australia is increasing.
• Multiple new resistance sources have been found and will be provided to breeding programs. Major and minor genes are being stacked into superior lines through speed breeding and will be handed over to breeders for further evaluation.
• Ascochyta rabiei (host specific pathogen causing Ascochyta blight) can be found on other non-host grain crops and weeds, but no symptoms are present. The importance of non-host inoculum as a source for infection of chickpea is still being investigated.
• Many Australian varieties will lose resistance if overseas Ascochyta blight isolates are introduced to Australia. Biosecurity is key to prevent this. The genetics of the overseas resistance are also being investigated to assist in improving resistance in the Australian breeding program.

Fungicide withholding periods

To protect pulses, there are several fungicides available and they vary in efficacy and 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. Table 2 lists some fungicides available for use in pulse crops, the harvest and grazing withholding periods, and some important use constraints.

Table 2. A selection of fungicides available to protect pulses from specified diseases. Always read and following the label directions, current labels can found on the manufacturers websites or at the APVMA (Public Chemical Registration Information System Search - portal.apvma.gov.au).

^ANote 63 days for export lambs. Do not graze or feed treated forage or fodder to livestock which may be used to produce milk for human consumption.

^BPermit PER92791, expires 31 October 2025.

^CPermit PER91123, expires 31 October 2024

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 taken and tested across the Southern region, which suggests that this 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 AFREN.

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

Pulse disease guide

Victorian and Tasmanian crop sowing guide data summary

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

Seed testing services are available at Agriculture Victoria, Crop Health Services (Phone 03 9032 7515, email chs.reception@agriculture.vic.gov.au) or SARDI (Phone 08 8429 2214, email sue.pederick@sa.gov.au)

Contact details

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