Emerging strategies for managing pulse foliar disease

Take home messages

• Foliar disease in pulses was infrequently reported in 2023, likely due to the dry spring. Foliar fungicides were likely unnecessary unless disease was observed, as most pulse foliar diseases require high humidity or recurring rain events.
• The first step to good disease management is choosing a resistant variety.
• Integrated disease management (IDM) practices also serve to minimise the risk of fungicide resistance developing.
• Sclerotinia disease in pulses was rare in 2023. However, severe Sclerotinia was reported in canola crops, reflecting a legacy effect of soil inoculum in paddocks sown to pulses in 2022.
• There were early reports of Botrytis disease in lentil and faba bean in July 2023. This is due to high inoculum load from 2022, coupled with above average June rainfall. Disease did not progress in the dry spring.
• Manage lentil varieties for Ascochyta blight based on pathotype 2 (Hurricane-virulent) ratings, as this pathotype is dominant in South Australia. A shift away from pathotype 1 (Nipper-virulent) towards dual pathotype 1 and 2 virulence has occurred.

Integrated disease management

To reduce the risk of foliar pulse disease and the risk of fungicide resistance developing, implement as many of the following practices each season.

• Maintain a 3–4-year gap between crops of the same type in the same paddock to reduce disease carryover from stubble and soil.
• Sow disease-resistant varieties to help reduce disease and the number of fungicide applications required.
• Sow clean seed or apply seed treatments to protect emerging seedlings. Seed and soil testing before sowing helps informs growers of disease risk.
• Avoid sowing near the previous year’s pulse crop, including neighbour’s stubble, to avoid infection by stubble-borne diseases.
• Monitor early for disease, especially near neighbouring stubble, in over-sown areas of the paddock and under trees or powerlines.
• Plan your foliar fungicide strategy early. Always mix and rotate fungicide groups, avoid consecutive use of the same group, and adhere to label restrictions. Spray ahead of rain, if disease is present.
• A pre-canopy closure spray will protect the base of the plant before the canopy closes over. Podding sprays may be required to protect the developing grain.
• Consider economics of continued disease management and crop end use (withholding periods, minimum residue levels).

For information on minimising the risk of fungicide resistance, including workshops, podcasts and the fungicide resistance management guide, visit the Australian Fungicide Resistance Extension Network (AFREN) at.

Disease ratings for pulse varieties are reviewed annually in the National Variety Trial (NVT) disease ratings review. This is usually finalised by early March and updated ratings are available from.

Sclerotinia white mould in pulses

Sclerotinia white mould (SWM) poses an increasing threat in southern Australian grain growing regions. SWM is caused by the soilborne fungus, 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.

Prevalence of SWM in 2022 vs 2023

The 2022 season was highly conducive for SWM and several lentil paddocks were severely affected in SA (Blake et al. 2023) and Vic (Fanning 2023), whereas SWM was sporadically reported in 2023 likely due to the drier conditions and decile 1/2 rainfall (BOM). Surveys of lentil crops conducted in SA in spring revealed disease incidence in four of six paddocks of 88–95% in 2022 (Blake et al. 2023), compared to disease incidence in four of five paddocks of 2–9% in 2023. In Victoria during 2022, 60% of paddocks had Sclerotinia with a greater proportion in the Mallee compared to the Wimmera. Despite a high risk moving into 2023, no Sclerotinia was observed in the paddock surveys due to environmental conditions. The legacy effect of SWM in lentil in SA was also shown through reports of severe Sclerotinia stem rot in canola in 2023 that occurred in paddocks sown to lentil in 2022.

Lentil trials examining yield loss, agronomic factors and varietal response to SWM

In 2023 at Long Plains in SA, trials were conducted to examine the yield loss from SWM in different lentil varieties (Table 1) and under different crop canopies manipulated by two times of sowing (Table 2). This site was selected as it had a high level of soil inoculum and high disease severity in 2022 (Blake et al. 2023). A low level of SWM symptoms were rated in the trials on 26 September 2023. Grain yield of lentil varieties was poorly correlated with their disease severity (R2=0.203); however, higher grain yield was achieved at the earlier time of sowing despite the higher level of disease symptoms. These trials will be repeated in 2024 in anticipation of more conducive environmental conditions for SWM disease at the site.

Table 1: Grain yield (t/ha) and SWM disease severity (% of wilted plants per plot) of lentil varieties at Long Plains SA in 2023. Least significant difference of means (5% level) shown for each variable.

Table 2: Grain yield (t/ha) and SWM disease severity (% of wilted plants per plot) of PBA Hurricane XT at two times of sowing at Long Plains SA in 2023. Least significant difference of means (5% level) shown for each variable.

In 2022 at Wagga Wagga, NSW, a lentil variety trial was conducted to assess yield loss from SWM and a high level of SWM developed. Unfortunately, continued wet weather through spring compromised results. Yields were highest in the Complete Control (fortnightly fungicide) treatments, but this was not always significant and yield response to a single foliar fungicide application at canopy closure did not always increase yields over the Nil treatment (Table 3). Plant infection was lowest in the Complete Control treatment, but there were no significant differences between the Nil and Canopy Closure treatments (Table 4). A single application of foliar fungicide at canopy closure did not provide adequate periods of protection under conditions of prolonged disease pressure. Interestingly, total sclerotia weight was highest in the Complete Control treatment, likely due to the retention of green leaf within the canopy (Table 5).

Table 3: Effect of foliar fungicide treatment to manage Sclerotinia disease (SWM) on grain yield averaged across five lentil varieties sown at Wagga Wagga, NSW 2022.

Table 4: Effect of foliar fungicide treatment on the incidence of Sclerotinia disease (SWM) (% plants infected along 2m row) averaged across five lentil varieties sown at Wagga Wagga, NSW 2022.

Table 5: Effect of fungicide treatment to manage Sclerotinia disease (SWM) on production of sclerotia averaged across five lentil varieties sown at Wagga Wagga, NSW 2022.

Management of SWM in pulses

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 pasture and broadleaf weed species are also hosts. PREDICTA B testing of Sclerotinia spp. soil inoculum levels after harvest will inform growers of disease risk. The new GRDC investment (DPI2206-023RTX) is showing that behaviour of Sclerotinia disease in each crop species is unique. The behaviour of SWM in pulses is very different to that in canola and should be managed as such, as the plant to plant spread of the disease, for example, is unique to lentil.

Foliar fungicides will go part way to managing the disease, but basal infections cannot be managed. There are a limited number of fungicides registered for control of Sclerotinia disease in pulse and canola crops. For more information access the Extension Aus website.

For information on Sclerotinia in canola access the GRDC website

Botrytis disease of lentil and faba bean

Botrytis grey mould (BGM) of lentil and chocolate spot (CS) of faba bean were infrequently reported during 2023 in SA. Early reports of BGM on lentil in SA and Vic in mid-July 2023 following the decile 9/10 rainfall in June (BOM) did not progress in spring, likely due to the dry seasonal conditions.

Botrytis disease is favoured by mild temperatures (15–25°C) and high humidity (>70%). It can also develop slowly in cool conditions, particularly with a high inoculum load, humidity, or a full soil moisture profile. Early sowing or high seeding rates can create a warm humid microclimate under dense canopies, ideal for rapid disease development in spring. In lentils, symptoms start as pale grey to light tan leaf lesions without black spots in the centre. Severe infections may result in easily liberated fluffy grey fungal material when the canopy is parted and eventual crop collapse. Faba beans show initial symptoms as red-brown discrete scattered spots over leaves and flower petals. With severe infection, lesions merge causing rapid defoliation and flower abortion within a few days.

The development of cost-effective IDM strategies for control of Botrytis disease (and Ascochyta blight, AB) of lentil and faba bean is the focus of a new national three-year GRDC investment led by Agriculture Victoria (DJP2304-004RTX; 2023-2026). This will complement validation research being conducted in the SARDI/UoA-led state-wide Grain Legume Validation project (GRDC investment UOA2105-013RTX, 2021-2025). However, due to the dry spring in 2023, Botrytis disease did not develop in these trials at Maitland, Riverton or Tarlee in SA.

Growers are encouraged to implement IDM best practice (see above). Sowing disease resistant varieties helps reduce disease severity and preserve or increase grain yield (Blake et al. 2023;). Ensure that varietal selections are compatible with the disease risk profile, paddock history, local climate, soil type, and agronomic management. Disease risk will be higher in regions where canopy closure is achieved, as often climatic conditions in these regions are more disease conducive.

Managing BGM in lentil with foliar fungicides

Several fungicides are registered for control of BGM in lentil. Newer fungicides with dual modes of action, as well as Filan® and Sumisclex®, show superior disease control and grain yield preservation in a high disease situation (Blake et al. 2023). However, judicious use of fungicides along with cultural practices and crop rotation, is critical to protect the current chemistries.

Two new coformulations (DMI+SDHI and DMI+QoI) of three new active ingredients not currently registered on pulses are anticipated for registration in the next 12–24 months by BASF (I. Francis, pers. comm.).

For medium to high rainfall regions, apply a pre-canopy closure spray regardless of the BGM resistance rating. Varieties rated MRMS and less may require additional sprays before rain in high-risk situations every 2–3 weeks. Follow-up sprays may be necessary in MR varieties or during highly conducive disease seasons. A podding spray may also be required to protect the developing grain from both BGM and AB. Always follow label directions. In low rainfall zones, the economic justification for fungicide sprays should consider the likelihood of achieving canopy closure and of ongoing humid conditions that favour the disease. This is particularly important with early sown crops.

In 2023, Agricultural Innovation & Research Eyre Peninsula (AIR EP) and South Australian Grain Industry Trust (SAGIT) co-funded research to examine the effectiveness and economic benefit of different fungicide strategies on lentil in a warm, low rainfall climate with short, mild winters. Trials were conducted at Mount Cooper and Mount Damper on the Eyre Peninsula, however no disease developed as conditions were not conducive. Fungicide spray(s) were uneconomical in a decile 1 rainfall spring in this region.

Managing CS in faba bean with foliar fungicides

PBA Amberley, rated MRMS, is the most resistant faba bean variety to CS but still benefits from foliar fungicide application. Several fungicides are registered or permitted for control of CS in faba bean, however application timing is critical. During 2022, reports of a mistimed spray(s), often due to persistent rain restricting paddock access, were associated with moderate to severe CS, crop lodging, and occasional crop failure. Proactively control CS with early-mid flowering sprays before symptoms appear. Follow-up sprays are needed in high rainfall situations and high biomass crops. Crop areas around trees and under power lines can be CS hot spots if not reached by spray equipment.

Monitoring the lentil Ascochyta blight pathogen population

Annual controlled environment testing of 29 Ascochyta lentis isolates collected from SA in 2022 was conducted in 2023 on an expanded lentil differential host set that included alternative sources of resistance to AB (Table 6). This is the second year in a row that no isolates were characterised as pathotype 1 (Nipper-virulent). A shift towards pathotype 2 (Hurricane-virulent), and dual virulent isolates that combine both pathotypes 1 and 2, has occurred (Figure 1). Of the isolates tested, 90% were capable of infecting PBA Hurricane XT which is currently rated MRMS to AB pathotype 2. Twelve of 29 isolates (41%) were capable of infecting PBA HighlandXT and five of 29 (17%) were capable of infecting PBA Jumbo2.

Monitor and proactively manage lentil varieties for AB based on the current NVT rating for pathotype 2. If disease occurs, plan to spray before rain, mixing and rotating modes of action. Where AB is present with persistent wet weather before harvest, pod infection may cause seed staining and quality downgrades. Podding sprays may be necessary in a wet spring; always adhere to withholding periods and follow label directions for use.

Table 6: Twenty-nine Ascochyta lentis isolates collected in 2022 from SA were inoculated onto a lentil host differential set in controlled environment conditions in 2023. Entries in the table are the number of isolates per category.

Key: R = resistant, MR = moderately resistant, MRMS - moderately resistant moderately susceptible, MS = moderately susceptible, S = susceptible

Figure 1. Annual testing of Ascochyta lentis isolates (n) collected from 2015 to 2022 from SA and VIC and their pathotype characterisation. Legend: P1 = pathotype 1, Nipper-virulent; P2 = pathotype 2, Hurricane-virulent; dual = combined pathotype 1 and 2; Not A. lentis = did not infect susceptible lentil check line.

Diseased samples of Ascochyta blight and Sclerotinia sought

Diseased samples of pulses with AB, and pulses and canola with Sclerotinia, are sought by SARDI for GRDC investments monitoring pathogen populations and changes in varietal resistance. If you can help, please contact Sara Blake or Mohsen Khani for a collection kit that includes sample envelopes and a return Express Post envelope.

Diagnostic plant samples

Send by Express Post to Pulse Pathology Plant Diagnostics SARDI, Locked Bag 100, Glen Osmond, 5064. Dig up whole symptomatic and asymptomatic plants and send with roots wrapped in damp (not wet) paper towel. Send at the beginning of the week, so the parcel does not get held up in the post. Please email PIRSA to notify the team that the plants are coming.

Crop protection products for pulses

For current registrations including minor use permits, visit Grain Producers Australia or APVMA.

Acknowledgements

The authors wish to thank the significant contributions of growers through both trial cooperation and the support of the GRDC, AIR EP and SAGIT. The continued technical assistance from SARDI Clare Agronomy and SARDI Pulse Pathology is gratefully acknowledged.

AIR EP/SAGIT project code: AEP1422

References

Blake S, Khani M, Krysinska-Kaczmarek M, Hill K, Giblot-Ducray D (2023)Discovery studies on sclerotinia white mould in lentil in South Australia. Australian Pulse Conference, Toowoomba, Australia.

Fanning J (2023) Pulse disease guide 2023. Agriculture Victoria, March 2023

Resources

Seasonal disease reports – subscribe to SA Crop Watch e-newsletter

2024 South Australian Crop Sowing Guide 

Contact details

Sara Blake
GPO Box 397, Adelaide SA 5001
0411 105 572
sara.blake@sa.gov.au
@Sara_N_Blake