New approach needed for successful pulse management in low rainfall environments

Take home messages

• Current recommendations for pulse management are based on medium and high rainfall zones and these strategies are not always economical for growers in low rainfall regions.
• Ability to control foliar diseases needs to be carefully considered prior to growing a pulse crop.
• It is important to follow an integrated disease management approach, monitor pulse crops for disease infection and apply fungicides at the first sign of disease prior to rain.
• Lentil is extremely sensitive to Group C herbicide use in dry conditions and herbicide choice, rate and application timing are critical in reducing risk of crop injury.
• Lentil crops are versatile, and hay can be cut to salvage a financial return where lentil is severely droughted or frost damaged.

Background

Pulse crop production has expanded into the low rainfall cropping regions of South Australia (SA) in the last decade, as adoption of direct drilling and continuous cereal cropping has increased the need to include break crops. The expansion is also a result of recent high grain prices for some pulse crops and the developments in pulse breeding, particularly the introduction of varieties with improved herbicide tolerance characteristics and varieties better adapted to low rainfall environments. Faba bean, chickpea, lentil, vetch and lupin production has increased since 2012, with the largest increases in area sown to chickpea, lentil and vetch (Figure 1). Field pea is the only pulse that has seen a reduction in production area, with the reduction in part due to the disease risk for field pea and higher grain prices for alternative pulse options. The Mid North region of SA has seen the largest reduction in field pea production area and has instead seen an increase in faba bean and lentil production. The western and eastern Eyre Peninsula has seen a small decrease in field pea production and an increase in lentil and vetch production, while the Lower Murray and the Murray Mallee regions have seen an increase in chickpea, lentil and vetch production area. While growers in low rainfall regions have increased their production area to pulses, the challenge of best management strategies for resource and economic efficiency remains.

Figure 1. Change in production area (ha) of pulse crops in the South Australian low rainfall cropping regions, shows an increase in lentil, chickpea and vetch production, 2012 to 2020 (1).

The majority of pulse management research is conducted in medium and high rainfall zones and strategies developed in these environments are often not viable or economical for growers in low rainfall regions. To improve grower confidence in pulse production within the low rainfall region there is a need for pulse management strategies developed specifically for low rainfall environments. In particular, novel approaches and management strategies to reduce or diversify economic risk, as well as strategies to reduce input costs without compromising production potential. This paper highlights refined approaches to pulse management for low rainfall environments, including disease management and lentil herbicide management. A comparison between vetch and lentil production potential and optimum seeding rate is also discussed, in view of the expansion of these two crops and an increased interest in the potential of lentil production for grazing or hay.

Results and discussion

Disease management

The Australian pulse industry experiences a loss of $74 million per year from disease infection, with the highest disease losses occurring in field pea and chickpea (Murray and Brennan, 2012). Fungicide seed dressings and multiple foliar applications are highly recommended for field pea and chickpea as there is currently no varietal resistance to Ascochyta blight (AB). However, the cost of these applications is not economical in low rainfall environments where grain production is low. It is important to keep in mind the cost of fungicide products and ensure label directions for use are followed. Applications of newer fungicide products such as Aviator® Xpro® can cost almost double that of Mancozeb® ($17.66/ha) and cannot be applied after early flowering unlike the latter product.

Disease infection risk can be low in pulse crops in low rainfall environments. However, regular crop monitoring and disease management strategies are still important as severe disease infection can occur in higher rainfall seasons if left unmanaged. The best approach to disease management is an integrated approach, combining the selection of a resistant variety, use of clean seed, paddock hygiene and the application of fungicides. It is important to implement a three to four year break between crops of the same type, revise cultivar selections and avoid sowing in paddock(s) in close proximity to previous year’s crops (Blake et al., 2019). Crop sowing guides and GRDC Grow Notes provide key and up-to-date information on variety resistance characteristics and disease management approaches. The subsequent sections highlight the key considerations for disease management in low rainfall environments for the commonly grown pulse crops.

Field pea

For field pea, the control of blackspot with fungicides is not economically viable where grain production is less than 1.5t/ha. Where grain production potential is greater than 1.5t/ha, newer fungicide options have been effective in reducing disease and improving grain yield in early sown crops and high disease situations (Walela et al., 2018). Blackspot can be reduced using a fungicide strategy of P-Pickel T® seed dressing combined with two foliar fungicide sprays (four to nine weeks post sowing and again at early flowering). Predictions of blackspot risk and spore release times in each field pea growing district can be obtained through Blackspot Manager online.

An integrated disease management program is very important for vetch production as there are few fungicides registered for use in this crop. Some of these registered fungicides have long withholding periods, and therefore, these should be avoided if the vetch crop is being cut for silage or hay destined for the dairy industry or grazed (GRDC GrowNotes - Vetch, 2018). It is important to consider the ability to control AB in vetch, as well as botrytis grey mould (BGM) and rust in higher rainfall seasons or where crops grow large quantities of biomass. There are fungicides registered for the control of BGM but the need for multiple sprays in conducive seasons may not be economical (Davidson and Noack, 2018). Grazing vetch will open up the canopy allowing it to dry out and reduce any disease spread. Rust can impact vetch growth and yield and it is very important not to graze or cut infected vetch crops for hay or silage as it can induce abortions in pregnant stock (GRDC GrowNotes - Vetch, 2018; Davidson and Noack, 2018).

Lentil

Lentil crops should be monitored for AB, as well as BGM in higher rainfall seasons or where crops grow large canopies. Growers should monitor lentil crops for disease infection and plan to spray infected crops ahead of rain fronts during podding to protect the developing seed. Fungicides may be required in wet springs to control BGM. There are lentil varieties with high disease resistance ratings (e.g., PBA Jumbo2) that can be utilised to reduce the need for fungicide applications without compromising yield potential.

Faba bean

Faba bean crops also need to be monitored for AB and chocolate spot (CS) as well as rust. Growers should monitor faba bean crops for AB infection and plan to spray infected crops ahead of rain fronts during podding to protect the developing seed. There are faba bean varieties with high AB resistance (e.g., PBA Samira) that reduce the need for fungicide applications. Flowers are particularly susceptible to CS and fungicides may be required during wet springs to protect against this disease. Growers should monitor crops for rust and spray at the first sign of disease.

Chickpea

In recent years high levels of AB infection have been found in chickpea crops across SA, even in lower rainfall environments. This has seen a reduction in resistance ratings in commercial varieties, leading to all varieties being rated as either susceptible or moderately susceptible. Growers need to carefully consider their risk of AB infection and their ability to effectively control the disease prior to making the decision to grow chickpea in the southern region. It is essential that all chickpea seed is treated with a thiram-based fungicide seed dressing to prevent early infection on seedlings, as the disease will survive on stubble and organic matter for numerous years. It is important to monitor crops for signs of infection and apply fungicides ahead of rain, particularly during reproductive growth stages, to protect developing seeds.

Lentil herbicide management

Herbicide choice and application timing is important to reduce risk associated with lentil production, particularly as lentil is extremely sensitive to Group C herbicide use in dry conditions. Applying herbicide prior to sowing is considered a lower risk option than a post-sowing pre-emergent (PSPE) application. Herbicide application incorporated by sowing (IBS) will disperse the herbicide so that it does not sit close to the seed, thereby reducing risk of crop injury. Herbicides applied PSPE are at a higher risk in low rainfall environments as the first rainfall event post application can leach herbicide into the seed bed. Crop injury from herbicides can result in reduced grain yield, nitrogen fixation, and weed competition, and increase the risk of soil erosion over summer.

Preliminary research was undertaken at Minnipa on neutral to alkaline clay loam soil to assess the risk of commonly used Group C herbicides on lentil. Terbuthylazine expressed a lower safety level and higher economic risk than diuron and metribuzin, with lentil generally more sensitive to terbuthylazine than other pulse crops (Figure 2 and Figure 3). These trials were expanded to new locations and soil types in 2020 to assess the risk of stacking Group C and Group B herbicides on Group B tolerant lentil, PBA Hallmark XT. Two trials were sown on different soil types at Tooligie. Crop injury occurred from metribuzin, with minimal damage from IBS application and chlorosis from PSPE application (Table 1). Terbuthylazine caused minimal crop injury on lighter soil types at Tooligie, in the 2020 season.

Figure 2. Reduced grain yield production in lentil where terbuthylazine was applied pre-emergent in clay loam soil at Minnipa, 2018. Bars labelled with the same letters are not significantly different (P<0.05).

Figure 3. Reduced gross margin in lentil where terbuthylazine was applied pre-emergent in clay loam soil at Minnipa, 2018. Bars labelled with the same letters are not significantly different (P<0.05).

Table 1. Mean crop injury score (0 = no crop damage, 9 = crop death) for damage caused by Group C and/or Group B herbicides applied to PBA Hallmark XT lentil at Tooligie, 2020. Scores with different associated letters are significantly different (P<0.05). IBS = incorporated by sowing, PSPE = post-sowing pre-emergent, POST = post emergent.

Herbicide choice will differ depending on an individual grower’s attitude towards risk and experience with products, soil type, target weed populations, environmental conditions, herbicide solubility, and leaching rate. Often a combination of herbicides with different solubility and leaching rates can be used to reduce the risk of damage while targeting a wider spectrum of weeds. The solubility and binding rates of Group C herbicides used in lentil vary between products (Table 2). The solubility of each herbicide influences how much rain is required for herbicide incorporation and the likelihood of the herbicide moving down the profile (Congreve and Cameron, 2019). Herbicides with low solubility (diuron and terbuthylazine) require good soil moisture and rainfall to achieve incorporation and are less available in the soil moisture than herbicides with high solubility (metribuzin). A herbicide with high solubility can move more readily within the soil and is more likely to cause off-target damage, as seen on sandy loam soil at Tooligie (Table 1). The binding or absorption ability of herbicides is affected by the soil texture and soil organic matter (Congreve, 2015). Heavy soils and soils with high levels of organic matter have greater binding ability and will absorb more herbicide. For this reason, higher application rates are required to achieve successful weed control as there is less herbicide available in the soil water for root uptake.

Table 2. Label instructions, solubility rate and binding ability of commonly used Group C herbicides in lentil production. IBS = incorporated by sowing. PSPE = post-sowing pre-emergent.

Vetch in comparison with lentil - reducing inputs and diversifying production

With a reduction in area sown to field pea, growers are choosing to grow vetch, a versatile break crop, and are considering the potential of other pulse break crop options for alternative end uses. There are many unfavourable aspects of vetch production, including poor early weed competition, limited herbicide options, hard seediness of some varieties, poor harvestability and market access. Using lentil for grazing or hay is growing in interest among low rainfall growers, which initiated research trials comparing biomass and grain production of vetch and lentil sown at multiple seeing rates, at four trials sites in 2020. The seeding rates compared recommended target plant density (120 plants/m² for lentil and 60 plants/m² for vetch) with a target density of half and three-quarters of the recommended rate to assess whether input costs could be reduced without compromising production potential. Higher than recommended rates were not included, as high plant density crops increase the risk of disease infection and lodging and reduce the resource efficiency due to larger canopies. At three of four sites seeding rate could be reduced by a quarter without compromising biomass or grain production in 2020 (Table 3). Reducing the seeding rate further to half of the target density did reduce production at some sites. A seeding rate that is too low exposes the crop to aphid infestation and weed establishment and the crop is more difficult to harvest. Previous preliminary trials on seeding rate in lentil at Melton and vetch at Willowie support these findings that seeding rate can be reduced without compromising production under some seasonal conditions. Additional trials are required in future seasons to further validate this research across a range of seasonal conditions and soil types.

Table 3. Biomass and grain production (t/ha) responses to multiple seeding rates of lentil and vetch at four sites in 2020. LSD = least significant difference (P<0.05). n.s. = not significant.

Where vetch is not favoured as a break crop, lentil can be a versatile option. Lentil hay could be cut to salvage a financial return where the crop is severely affected by frost, heat or drought. For the 15 break crop trials in the southern region, lentil was better than (vetch < lentil) or equal to vetch (vetch = lentil) for biomass production in seven trials, for grain production in 10 trials and for profit in nine trials (Table 4). Lentil production and profit was greater than vetch at two sites and in these cases, crops were affected by frost or dry spring seasonal conditions. Lentil can be utilised as a lower risk and versatile crop option as an alternative to vetch, with greater market access for lentil grain and increasing interest in lentil hay. Feed analysis shows minimal difference in the feed quality of lentil and vetch hay (Table 5), and in recent years lentil crops have been profitable where hay was cut due to severe frost damage that would have resulted in no grain production.

Table 4. Frequency of break crop trials where vetch biomass and grain production and profit from grain production was equal, greater than, or less than lentil, 2017-2020.

Table 5. Feed analysis results of lentil and vetch cut for hay at early pod development growth stage.

Conclusion

The majority of pulse management recommendations have been developed for medium and high rainfall zones. These strategies are unlikely to be viable and economical for low rainfall regions or in low rainfall seasons and there is a need for specifically developed management strategies that reduce inputs costs without compromising on production potential.

The ability to control foliar disease in pulse crops needs to be carefully considered prior to growing these crops and an integrated approach is essential. For disease management it is important to follow recommendations on seed and paddock hygiene, select varieties with improved disease resistance where possible, monitor paddocks for disease infection and apply fungicides at first sign of disease prior to rain fronts.

Lentil is extremely sensitive to Group C herbicide in dry conditions and herbicide choice is important in reducing risk of crop injury. Herbicide choice will differ depending on an individual grower’s attitude towards risk and experience with products, soil type, target weed populations, environmental conditions, herbicide solubility and leaching rate. It is important to remember that product label rates, plant-back periods and directions for use must be adhered to.

Lentil can be a versatile pulse option where vetch is not favoured or where lentil crops grown for grain are severely drought or frost effected. Seeding rate of lentil and vetch can be reduced without compromising on production potential but it is important to not reduce rates too low as this can reduce production and will leave crops exposed to weed and aphid infestations.

Acknowledgements

The research undertaken as part of these projects (GRDC project codes DAS00162A and DAV00150) 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.

Useful resources

South Australian Crop Sowing Guide

Grow Notes

References

PIRSA. Crop and Pasture Reports South Australia. 2012-2020.

Murray G, Brennan J. The current and potential costs from diseases of pulse crops in Australia. 2012.

Blake S, Farquharson L, Kimber R, Davidson J, Walela C, Hobson K. Ascochyta blight in intensive cropping of pulses. In: ORM, editor. GRDC Grains Research Updates; Adelaide2019.

Walela C, Roberts P, Mould R, Spriggs B, McMurray L, Davidson J. Ascochyta blight severity and yield response to fungicides in field pea. 2018.

GRDC. GRDC Grow Notes - Vetch. 2018.

Davidson J, Noack S. Disease management of pulses in low to medium rainfall zones. In: ORM, editor. GRDC Grains Research Updates2018.

Congreve M, Cameron J. SOIL BEHAVIOUR OF PRE-EMERGENT HERBICIDES IN AUSTRALIAN FARMING SYSTEMS - a reference manual for agronomic advisers. October 2019 Soil behaviour of pre-emergent herbicides for agronomic advisers. GRDC publication, Australia; 2019.

Congreve M. Pre-emergent herbicides - fact sheet. 2015.

Contact details

Sarah Day
70 Farrell Flat Road, Clare SA 5453
08 8841 2404
Sarah.Day@sa.gov.au
@Sarah_Day

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