Pulse disease, agronomy and variety update - 2021

Take home messages

• New varieties: Several new pulse varieties are now available for growers offering specific agronomic and regional advantages. The first two field peas released with imidazolinone ‘imi’ tolerance, GIA Kastar and GIA Ourstar, along with a PBA Jumbo2 type lentil, GIA Leader. A large seed imi lentil, PBA Kelpie XT, plus a new desi chickpea, CBA Captain and a large seeded kabuli PBA Magnus.
• Disease management:
  • selecting a more resistant variety will reduce grain yield losses, however the faba bean, PBA Amberley will require fungicide during optimum disease conditions to prevent grain yield losses.
  • Fungicide strategies incorporating newer fungicide actives are providing equal or better disease control than older actives in faba beans and chickpeas.
  • Inter-row sowing into standing cereal stubble, compared to slashed stubble, is almost as effective at reducing chickpea grain yield losses due to ascochyta blight, as choosing a moderately susceptible, compared to a susceptible variety.
• Lentil pod drop & architecture:
  • Pod drop was not a major issue in 2020, yet the economic loss in a more susceptible variety, PBA Hallmark XT, was equivalent to $55/ha more than a more resistant variety PBA Jumbo2.
  • ‘Spreading varieties’ (eg PBA Jumbo2) showed no response to sowing direction or row spacing. However, the ‘Erect varieties’ (eg PBA Bolt) had 6% lower grain yield sown N-S compared with E-W and were 9% higher yielding in narrow rows compared to wide rows.
• Weed management and herbicide tolerance traits:
  • Several new novel herbicide tolerance traits continue to be developed across all pulses. The improved tolerance to both Group I and C products, combined with the Group B tolerance that has been released will continue to provide growers with more options for improved weed control throughout the farming system.
  • Conventional herbicide tolerance, such as improvements in tolerance to registered products like Brodal® (Group F) in lentil (eg PBA Hallmark XT)is essential to maintain as these products form an essential component to the control of broadleaf weeds.

Introduction

Ongoing improvement in pulse varieties, combined with improved agronomic and disease management practices has seen pulses become essential to profitable farming systems in southern Australia. However, there are many emerging challenges and opportunities for ongoing research and development in partnership with industry:
Disease Management: Recently, there has been a varietal improvement in botrytis grey mould resistance with the faba bean, PBA Amberley. However, the varietal resistance of chickpeas to ascochyta blight has been overcome by new strains of the disease. In a positive note, several new fungicide products with new modes of action for pulses have been released. Both of these factors create new opportunities to improve and change disease management strategies, aiming to reduce inputs, while maximising profitability.

Plant architecture and pod drop in lentil: In recent seasons pod loss in lentil has been a significant issue in southern Australia resulting in significant losses across a range of varieties. At Curyo in 2019, significant difference across varieties was noted, with PBA Hallmark XT, an erect type, showing the most susceptibility among released varieties, while PBA Jumbo2, a spreading type, recording reduced pod drop. Row spacing, stubble height and sowing direction could all have an impact on pod drop, due to their impact on canopy architecture, which influences the movement of the canopies that occurs at maturity especially during high wind events. Investigating the interaction between varieties and agronomic practices could help to minimise pod loss.

Weed Management: Several new pulses are being developed with novel Group C and Group I tolerance in addition to the Group B tolerance that is observed in lentil and faba bean. These traits are creating opportunities for novel weed management practices plus improving the ability to grow the crops on soils where residual herbicides carryover is a significant issue.

In this paper we provide an update on the new pulse varieties and a snapshot of some key findings from recent disease and agronomic management research of relevance to the Wimmera. Several other issues will be discussed during the presentation, with full reports soon to be available through Online Farm Trials.

New varieties

Lentils

GIA Leader (tested as GIA1701L) is a new imidazolinone-tolerant, medium-seed-sized red lentil developed by Grains Innovation Australia (GIA) and available through PB Seeds for favourable lentil-growing areas with good soil types in medium to higher rainfall zones. This variety’s imi herbicide tolerance and tolerance to residual levels of sulfonylurea (SU) herbicide from previous cropping seasons is similar to current XT lentil varieties. GIA Leader has a plant type similar to PBA Jumbo2 and is mid to late flowering and maturity, making it well suited to early sowing. Provisional data indicates a good level of resistance to Ascochyta blight and BGM.

PBA Kelpie XT (tested as CIPAL1721) is a large-seed-sized, herbicide tolerant red lentil, released in spring 2020 through commercial partner Seednet. PBA Kelpie XT is an early to mid-flowering and maturing variety with a good resistance to Botrytis grey mould (BGM). PBA Kelpie XT has similar herbicide tolerance characteristics to other PBA XT lentil varieties but offers a larger seed type and higher yields than PBA Hurricane XT.

Chickpeas

CBA Captain (tested as CICA1521) is a medium-size-seed variety with broad adaptation to Victorian desi chickpea-growing areas. It has an erect plant type with good plant height and height to lowest pod. It is mid-flowering and mid maturing in Victorian growing environments and produces good grain size similar to PBA HatTrick, meeting the requirements of a ‘Jimbour type’, suitable for the subcontinent market.

PBA Magnus (tested as CICA1352) is large-seeded kabuli type with similar plant type to Genesis™ 090. It is mid-flowering and mid maturing and adapted to current kabuli-growing regions of Victoria and South Australia. It provides an excellent replacement for Genesis™ Kalkee with slightly larger seed size. Seed is available from PB Seeds.

Field Peas

GIA Kastar (tested as GIA2001P) is the first Kaspa-type field pea with improved tolerance to common in-crop and residual imi herbicides. It is mid flowering and early-mid maturing with an erect growth habit with a semi-leafless plant type, resistant to pod shatter at maturity. It produces uniform red to brown coloured seed coat, medium in size, marketable for human consumption in the Indian/Asian subcontinent. Seed available from AG Schilling & Co.

GIA Ourstar (tested as GIA2002P) is the first Dun type pea with improved tolerance to common in-crop and residual Group B herbicides (imi and SU). It is early-mid flowering and early-mid maturing and has similar plant type and growth habit to PBA Oura. It produces medium sized, light green to tan-coloured grain, marketable as human consumption or stockfeed. Seed is available from AG Schilling & Co.

Disease management highlights

Faba Bean Disease Management

Note: This section is an excerpt from Fanning et al. at the Victorian, GRDC Updates 2021 in Bendigo¹.

Chocolate spot (Botrytis fabae) in faba beans can cause significant grain yield loss and result in poor quality seed. Chocolate spot disease development can occur at most growing season temperatures, but the disease develops quickest when canopy humidity is high (~>70%) and temperatures are warm (15-25°C). These environmental conditions can differ between crops, depending on not only the prevailing weather but also the canopy density.

Impact of sowing rate

Field experiments at Lake Bolac and Lake Linlithgow showed that chocolate spot severity increased in faba bean plots as target plant densities increased from 5 to 45 plants per square metre, with similar results observed at both sites (Figure 1). The variety PBA Bendoc (rated moderately susceptible (MS)) had greater disease severity in all plant densities, compared to PBA Amberley (provisionally rated moderately resistant (MR)). Additionally, PBA Amberley had over 60% disease severity in high density (45 plants/m²) plots, equivalent to PBA Bendoc at a low density of 5-15 plant/m². This highlights that the ideal conditions for disease will still put pressure on the moderate resistance in PBA Amberley and result in grain yield losses. The chocolate spot resistance rating of faba bean is reviewed annually, so it is important to always check for up to date disease ratings.

Figure 1. Increasing plant density resulted in increasing chocolate spot severity in unsprayed plots atLake Bolac in a field trial planted 9 April 2020.

Varietal resistance and fungicide strategy

With the recent release of PBA Amberley (provisionally rated MR to chocolate spot) and the newer fungicide actives, it was important to review fungicide strategies against varietal resistance to determine if the number of applications required to prevent grain yield loss can be reduced. At five locations across Victoria (Dookie, Nhill, Gymbowen, Lake Linlithgow and Lake Bolac) experiments were conducted to compare varietal resistance and fungicide strategies. Only the Lake Bolac and Gymbowen results are presented in this paper. Newer chemistries including, tebuconazole + azoxystrobin (Veritas®), bixafen + prothioconazole (Aviator® Xpro®) and fludioxonil + pydiflumetofen (Miravis Star® - registration submission awaiting approval from the APVMA) were compared against older chemistries including carbendazim or procymidone (Table 1). The aim was to compare the newer chemistries applied at early flowering with the older chemistries at canopy closure. All treatments received a 4-node tebuconazole application to prevent cercospora leaf rot. Treatments were applied at early flowering as these newer chemistries were expected to have longer efficacy and this timing is the latest some of these products can be applied to comply with label directions. The Lake Bolac and Gymbowen experiments were sown 19 April and 23 April 2020, respectively.

At Lake Bolac, additional applications of carbendazim and procymidone were applied in addition to the fungicide treatments, as conducive disease conditions continued throughout the season and this site needed additional fungicide controls. In other experiments on these sites, it was difficult to control chocolate spot in susceptible varieties, even with fungicides. This 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 Lake Bolac and Gymbowen during 2020.

^A These fungicides are additional to all treatments receiving a tebuconazole application at the 4 to 6 node growth stage. At Lake Bolac there was significant disease pressure later in the season. Therefore, an additional two carbendazim (250 gai/ha) and an extra one procymidone (240 gai/ha, two extra procymidone applications on the carbendazim treatment) were applied alternately every 2-4 weeks to control the chocolate spot;

^B At Lake Bolac the first procymidone was applied at flowering;

^C This is a new product to Australia called Miravis Star® which is currently going through the registration and approval process;

^D The full control treatment is a rotation of fungicides applied to ensure minimal to no disease as a control in the experiment.

Disease epidemics varied between locations with no disease observed at Nhill and Dookie. Gymbowen, Lake Bolac and Lake Linlithgow all had chocolate spot, and a low level of cercospora leaf spot. All three sites with chocolate spot demonstrated similar results, so Lake Bolac is highlighted where disease was moderate (Table 2). PBA Bendoc had consistently more severe chocolate spot compared to the other varieties, with disease symptoms observed and progressing under the ‘Full Control’ fungicide treatment. In comparison, PBA Samira and PBA Amberley had the least disease severity. The fungicide treatment containing Fludioxonil + Pydiflumetofen resulted in disease severity similar to the ‘Full control’. These results highlight the requirement for fungicides to be applied to PBA Amberley to prevent severe disease.

Faba bean grain yield recorded at Lake Bolac and Gymbowen indicated greater fungicide efficacy in the newer chemistries, with Fludioxonil + Pydiflumetofen, providing higher yield gains compared to the other fungicide strategies. Economic benefit of applying the new chemistries, was similar to the older strategy involving carbendazim (Table 3 and 4).

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

^A These fungicides treatments are in addition to the tebuconazole application at the 4-6 node stage described in Table 1.

Table 3. Grain yield of four varieties, with seven different fungicide strategies applied at Lake Bolac during 2020. Percentage yield increase relative to untreated and economic advantage ($/ha) of each fungicide treatment is also presented.

^A These fungicides treatments are in addition to the tebuconazole application at the 4-6 node stage described in Table 1; ^B Different letters indicate pairwise significance (P<0.05); ^C Economic advantage 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/ton, and an application cost of $10/ha.

Table 4. Grain yield of four varieties, with seven different fungicide strategies applied at Gymbowen during 2020. Percentage yield increase relative to untreated and economic advantage ($/ha) of each fungicide treatment is also presented.

^A These fungicides treatments are in addition to the tebuconazole application at the 4-6 node stage described in Table 1; ^B Different letters indicate pairwise significance (P<0.05); ^C Economic advantage 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/ton, and an application cost of $10/ha.

Chickpea Disease Management – Benefits of Standing Stubble

Ascochyta blight is one of the major diseases of chickpea in Australia. Previous field observations indicate difference in disease activity in standing stubble vs burnt stubble where fungal infection initially spread along the crop rows in the direction of E-W stubble rows and that the infection rarely crossed over standing cereal stubble on to adjoining crop rows. Based on these observations, this trial at Dooen (Wimmera, Victoria) investigated the effect of sowing Genesis 090 (moderately susceptible) and PBA Striker (susceptible) into standing versus slashed cereal stubble, managed with or without fungicides on the severity of ascochyta blight during the season and the grain yields. The disease inoculated-nil fungicide plots did not receive any fungicides but were inoculated with ascochyta blight infected stubble seven weeks after sowing on July 16.

Key Result:

• Chickpea inter-row sown in to standing stubble and managed without fungicides had less disease severity resulting in improved grain yield: Genesis 090 and PBA Striker yielded 24% (339 kg/ha) and 132% (701 kg/ha) more in standing stubble compared to slashed stubble, respectively (Figure 2). Results demonstrate the benefits of standing stubble in a no-till farming system on disease management in chickpeas.

Figure 2. Grain yields and % grain yield increase in Genesis090 and PBA Striker inter-row sown into standing versus slashed cereal stubble, managed with (not inoculated) and without fungicides (+ inoculated) at Horsham, 2020. Different letters indicate significant differences (P<0.005).

Agronomic research highlights

Lentil Row Space/Direction – Impact on Pod Drop

In more recent cropping seasons several high wind events around the harvest period of lentil across southern Australia resulted in significant losses due to pod drop across a range of varieties. In preliminary trials at Curyo in 2019, significant variation was noted, with PBA Hallmark XT showing the worst susceptibility of released varieties and CIPAL1821 to be one of the worst breeding lines to drop pods. It has also been suggested that row spacing and direction could have an impact on the response, due to the structure of the crop canopy, and thus the movement that occurs at maturity during high wind events. These trials looked at combing agronomic and genetic responses to minimise yield losses from pod drop at harvest.

Two trials were conducted at Curyo (south Mallee) and Nhill (west Wimmera) comparing two row spacings; narrow (18 cm with 8 rows) and wide (36 cm with 4 rows), and two sowing directions North/South cf East/West. At both sites north/south was sown inter-row with the stubble direction, while east/west was sown across (perpendicular to stubble rows). In trials the N/S and E/W directions were analysed separately as they were sown as whole blocks. Eight varieties encompassing a range of agronomic characteristics were assessed (Table 5). In addition to the features listed below there are many subtle differences in growth habits and phenology that may influence response to the agronomic treatments. For example, PBA Jumbo2 has a vase type structure and can spread quite wide, while still standing at maturity. CIPAL1706L has short internodes and forms a shorter bushy structure. Aldinga tends to spread out and then lodge so that the plant is almost flat on the ground at harvest. In the erect varieties, PBA Bolt and CIPAL1821 tend to be very upright with limited branching. PBA Bolt has the best resistance to lodging at harvest. PBA Hallmark XT, while erect, tends to have more branches and will spread across the inter-row.

Table 5. Agronomic characteristics of varieties grown in row space x row direction trials at Curyo and Nhill in 2020.

¹R – resistant, MR – moderately resistant, MS – moderately susceptible, S – susceptible, U – unknown

Key Results:

• Pod drop was not a major issue in 2020 with minimal wind events. Sowing direction did not influence the number of pods dropped, while wide row treatments appeared to have slightly fewer pods dropped than narrow rows. PBA Hallmark XT lost the equivalent of 100 kg/ha ($65/ha) from pod drop and shattering, while PBA Jumbo2 only lost 16 kg/ha ($10/ha).
• ‘Spreading varieties’ (eg PBA Jumbo2) recorded no response to sowing direction or row spacing. However, the ‘Erect varieties’ (eg PBA Bolt) had 6% lower grain yield sown N-S compared with E-W and were 9% higher yielding in narrow rows compared to wide rows. Much of the variation could be explained by harvestability and lodging direction (Table 6).
• Profitability of lentils was excellent, with the estimated returns of approximately $1850/ha for PBA Jumbo2 grown at Curyo. Economic implications of row spacing and row direction will be further explored in coming seasons. Currently it is estimated that to sow, manage and harvest narrow rows compared with wide rows is an additional ($75/ha), so based on a long term average price of lentils at $600, a grower would need to consistently achieve an additional 125 kg/ha on narrow rows.

Table 6. Grain yield (t/ha) of lentil varieties and breeding lines sowing North/South (N-S) compared with East/West (E-W) and row spacing of 0.18cm and 0.36cm at Curyo in 2020.

Herbicide Tolerance – New Opportunities

Weeds are one of the major constraints when growing pulses successfully, due to poor tolerance to many residual herbicides applied to previous cereal and oilseed crops. There are also limited in-crop herbicide options available for the control of broadleaf weeds in pulses. The yield loss in pulses due to residual weeds in the Southern region has recently been estimated to be $7.5m, which equates to $10.03/ha².

Throughout the Southern Pulse Agronomy investment, a range of weed management and herbicide tolerance issues were investigated (Table 1), with a strong focus on the novel traits relating to Group B herbicide tolerance in lentil, faba bean and field pea, as well as Group C and I in lentil. In addition, the impact of crop topping and issues related to how to best utilise the herbicide(s) within a system e.g. soil type, depth, disc versus tyne, ripping, grasses, application timing and inoculation, were investigated.

Some key findings related to the novel traits are listed below:

Group B: The new field pea variety with tolerance to Group B herbicides, GIA Ourstar, showed no yield loss to various Group B herbicide simulated residues. However, the grain yield of GIA Kastar, was decreased by sulfonylureas residues but not imidazolinone residues. GIA Oustar will provide growers with greater confidence to grow field peas, even in areas where residues may be a risk for production. All new ‘imi’ tolerant lentil varieties have shown similar tolerance profiles to PBA Hurricane XT.

Group C: A breeding line, SP1333 has shown greater tolerance to a range of Group C herbicides compared to commercial cultivars, indicating a potential trait to improve tolerance within the breeding program. Similar to industry observations, PBA Jumbo was the most tolerant of current commercial varieties.
The metribuzin tolerant trait, developed through mutation breeding, potentially has poor cross-tolerance to other registered Group C herbicides. Initial investigations indicated that several breeding lines had significantly worse crop damage than conventional varieties (e.g. PBA Jumbo2) from products such as terbuthylazine, which is used widely as a pre-emergent spray in lentils.

Group I: The potential of new lentil breeding lines with tolerance to imidazolinone (Group B) and clopyralid (Group I) herbicides to tolerate clopyralid residues was highlighted along with the potential benefits for improved weed control through suppression of vetch with clopyralid residues was demonstrated.

Improving tolerance to Brodal®

Brodal Options® (diflufenican) continues to be an important component to control broadleaf weeds in lentils. Currently, many varieties suffer significant visual crop damage, but this does not often result in grain yield loss. Trials in 2019 observed that PBA Hallmark XT appeared to show significantly less crop damage than PBA Jumbo2. In 2020 a trial was conducted at Dooen (Wimmera) to develop a screening methodology and identify lentil varieties with higher tolerance to Brodal Options®.

Key Results:

• PBA Hallmark XT showed improved visual tolerance to Brodal®, compared with PBA Jumbo2, PBA Giant and PBA Jumbo (Table 7).
• Brodal Options® applied at 150 ml/ha at the 4-node crop growth stage none of the varieties suffered grain yield losses compared to other varieties (Table 7).
• For screening of germplasm, application post sowing, pre-emergent at rates greater than 300 ml/ha provided greatest discrimination between varieties.

Table 7. Symptoms of herbicide damage (0: no damage and 100: complete death; July 20) and grain yield of lentil varieties in response to application of 150 ml/ha Brodal® at 4-node crop growth stage at Horsham, 2020.

PBA Hallmark - Increasing seed size

In 2019, there were marketing issues with PBA Hallmark XT, where some processors where discounting the price received due to variability in seed size where seeds were not clearly fitting into the lentil seed size categories (i.e. small ‘Nipper type’ generally <4g/100seed, medium ‘Nugget type’ generally 4-5g/100seed or large ‘Jumbo’ type generally >5g/100seed). At Curyo in 2020, a trial investigated the stability of seed size in PBA Hallmark XT and its impact on growth, yield and seed quality.

Key Result:

Larger seed at sowing resulted in higher seed weight at harvest, but no significant differences in biomass and grain yield (Table 8).

Table 8.  Effect of sown seed size classes on germination, biomass (at flowering and maturity), grain yield, harvest index and grain weight of PBA Hallmark XT, at Curyo, 2020.

Acknowledgements

The research undertaken as a part of the project 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.

The authors are also grateful to all growers who have hosted trials on their farms and the input of industry representatives and colleagues to trial ideas and treatments.

Additionally, the authors are thankful to the technical teams of Agriculture Victoria and Southern Farming Systems, who have managed these trials.

Useful resources

Lentil Southern Region - GrowNotesTM, 2017.

Faba Bean Southern Region - GrowNotesTM, 2017.

Online Farm Trials – All trial results from the Southern Pulse Agronomy Research program are published here.

References

1. Fanning et al. 2021. Pulse Disease Research Update. In Victorian GRDC Research Updates- 2021, Bendigo, Victoria.
2. Llewellyn RS, Ronning D, Ouzman J, Walker S, Mayfield A, Clarke M (2016) Impact of Weeds on Australian Grain Production: the cost of weeds to Australian grain growers and the adoption of weed management and tillage practices Report for GRDC. CSIRO, Australia.

Contact details

Dr Jason Brand
Agriculture Victoria, 110 Natimuk Road, Horsham, Vic. 3400
0409357076
jason.brand@agriculture.vic.gov.au
@jasonbrand