Pulse disease research update

Take home messages

• It is anticipated that disease pressure on crops will be high going into 2023 due to carry over of high disease loads on stubble, seed and in the soil. Growers, therefore, should take a proactive approach to disease management this season.
• Where possible, choosing more resistant varieties will reduce grain yield losses caused by disease and reduce the reliance on fungicides.
• Testing seed and sowing disease-free seed will reduce disease carryover from 2022.
• 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 2022, it was shown that proactive management of pulse diseases was essential to maintain profitable production. Planning was critical and when plans were enacted based on the conducive seasonal conditions, there was reduced disease severity and increased profitability.

Adequate soil moisture and warm soil temperatures meant crop establishment during 2022 was early in many cases, with canopy closure earlier than average. Consistent rainfall provided a long season and conducive conditions for disease development throughout Victoria. Increased disease pressure resulted in varieties being at their most susceptible in the 2022 season and proactive disease management plans were the most successful. However, environmental conditions further exacerbated the disease situation in many pulse crops.

Seed testing

In 2023, it is important to sow seed with a minimal amount of disease to ensure desired plant establishment and minimise disease carryover. With multiple diseases present in many pulse paddocks during 2022, it is important to consider the implications for 2023 with retaining seed. Many diseases can carry over with the seed, either as sclerote contamination in grain (Sclerotinia white mould and Botrytis grey mould (BGM)) or infected seed (BGM and Ascochyta blight). Seed can be tested for disease at state laboratories (see Useful resources).

Botrytis disease management

General

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 Botrytis cinerea. Therefore, disease can spread readily between susceptible pulse crops or from previously infected stubbled. 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 make 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.

During 2022, high canopy humidity combined with early canopy closure produced conducive conditions for Botrytis to establish early in the season. Continued conducive conditions contributed to more reproductive lifecycles, increasing disease pressure. Botrytis development can occur at most growing season temperatures, but disease development is quickest when canopy humidity is high (greater than 70%) and temperatures are warm (15–25°C). These environmental conditions can differ between crops, depending on the prevailing weather and canopy density.

Faba bean experiments

With the 2022 season highly conducive to Chocolate spot, the 2020 Hamilton trial results (next to Lake Linlithgow, Vic) are highly relevant to the recent season. This experimental site was comparable to many Medium rainfall zone (MRZ) areas during 2022 and provides data to support the management advice around Chocolate spot.

Newer dual active fungicides including, tebuconazole + azoxystrobin (Veritas®), bixafen + prothioconazole (Aviator® Xpro®) and fludioxonil + pydiflumetofen (Miravis Star®) were compared against the single active chemistries carbendazim or procymidone (procymidone is now permitted under the permit PER92791, Table 1). All treatments received a 4-node tebuconazole application to prevent Cercospora leaf spot. Treatments were applied at early flowering as these newer chemistries were expected to have longer efficacy and this timing is the latest permissible application timing for Aviator® Xpro® and Miravis Star®.

It was a very conducive year, hence additional applications of carbendazim and procymidone were applied in addition to the fungicide treatments to be more realistic in a very conducive environment.

These additional fungicides struggled to limit disease progression and highlights the need for proactive disease management, as disease epidemics can develop rapidly.

Table 1: Fungicide treatments and timings in faba bean experiments conducted at Hamilton during 2020.

^AThese fungicides are additional to all treatments receiving a tebuconazole application at the 4–6 node growth stage. There was high disease pressure later in the season. Therefore, an additional two carbendazim (250g ai/ha) and an extra one procymidone (250g ai/ha), or two extra procymidone applications on the carbendazim treatment were applied alternately every 2–4 weeks to control Chocolate Spot. Carbendazim and Procymidone were applied up to a maximum of 2 consecutive applications.

BProcymidone can be applied under PER92791 on faba beans.

PBA Bendoc and Fiesta consistently showed higher levels of Chocolate spot compared to PBA Samira and PBA Amberley, with disease symptoms observed and progressing under all treatments (Table 2). These results highlight the requirement for fungicides to be applied to all varieties, to prevent severe disease.

Faba bean grain yield indicated greater fungicide efficacy in the dual active chemistries, with fludioxonil + pydiflumetofen, providing higher yield gains compared to the other fungicide strategies (Table 3). The economic benefit of applying the fludioxonil + pydiflumetofen was similar to the strategy involving carbendazim with the canopy closure application, further highlighting the need to minimise disease early in the season (Table 4).

Table 2: Chocolate spot severity in four varieties with different fungicide strategies applied at Hamilton, assessed on 20 October 2020.

^AFungicide strategies are described in Table 1.

^BDifferent letters indicate significant differences (P<0.05) between means of varieties or treatments.

Table 3: Grain yield of four varieties with seven different fungicide strategies applied at Hamilton during 2020.

^AFungicide strategies are described in Table 1.

^BDifferent letters indicate significant differences (P<0.05) between grain yield means across varieties and treatments.

Table 4: Gross margin ($/ha) of four varieties with seven different fungicide strategies applied at Hamilton during 2020.

^AFungicide strategies are described in Table 1.

^BGross margin was calculated as the grain yield gains minus the cost of the fungicide treatments. Chemical prices were an average of three chemical resellers prices provided, grain price was assumed to be $400/t and an application cost of $10/ha.

Sclerotinia white mould

Sclerotinia white mould (SWM) is a damaging disease that can infect many pulse crops including lentil, chickpea, faba bean, vetch, field pea and lupin. It can also affect canola, pasture legumes and many weeds. This disease poses its greatest risk during seasons with prolonged damp conditions. Currently, there is limited knowledge on its control, but several fungicides currently registered or under permit for other diseases in pulses and could be used in Victoria. Sclerotinia was widespread in Victoria during 2022 and sclerotes can last in the soil for over 15 years. Research into management strategies is in the preliminary stages, with a focus on determining whether varietal resistance exists, and research on the incorporation of integrated disease management strategies.

With limited management knowledge, growers are advised to monitor for infected paddocks, consider non-host crops and, where possible, ensure they are sowing clean seed.

Sowing time

Delaying sowing can be an effective disease management tool, as it delays canopy closure and reduces the number of disease cycles that can occur in a season. It is important though to offset this with the potential yield reductions from late sowing. It is a balance and should be based around plant establishment, noting that sowing, germination and establishment times vary. If paddocks are sown early in warmer soils, plants may establish early, thus increasing the disease risk. One example of this is from a chickpea Ascochyta blight experiment in Horsham during 2022 where significant differences (P<0.005) in disease severity were observed. The variety Genesis 090 had 42% disease severity when sown in May, compared to 22% disease severity when sown in July. This is only an example and sowing times should be adjusted for different crops and regions.

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 fungicides and many crops only have single active fungicides applied at multiple times throughout the season. Therefore, there is a high probability that we may observe fungicide resistance if growers do not take preventative steps now.

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 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.

Conclusions

With high disease levels during 2022, it’s important to sow clean seed during 2023 to ensure desired plant establishment and reduce disease carryover. Plan a disease management strategy early that incorporates varietal resistance, paddock rotations, reliable agronomy practices (sowing time, interrow sowing, nutrition), rotation of fungicide groups, and strategic fungicide applications. Without a solid strategy, grain yield losses of greater than 90% can be experienced 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 author would like to thank them for their continued support. Appreciation is given to the Agriculture Victoria Southern Pulse Agronomy and Field Crops Pathology teams, the Southern Farming Systems research team and the growers and agronomists who have assisted with these experiments.

Useful resources

Pulse disease guide

Victorian and Tasmanian crop sowing guide 

Crop protection products details including Minor Use Permits, can be viewed at the Australian Pesticides and Veterinary Medicines Authority (APVMA) websit

Seed testing services

Agriculture Victoria, Crop Health Services
03 9032 7515
chs.reception@agriculture.vic.gov.au

SARDI
08 8429 2214
sue.pederick@sa.gov.au

Contact details

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