The watch outs for pulse diseases in 2017

ɸExtra technical comment by Protech Consulting Pty Ltd

Take home messages

  • Consider previous herbicide use, crop rotation history, soil type (including pH) and paddock location when deciding to sow a pulse crop, as these factors can influence crop performance and disease risk.
  • Not all pulse diseases can be managed with foliar fungicides — consider other management options when sowing pulse crops.
  • Foliar disease management is integral to growing faba beans. Understand the critical periods for disease management and foliar fungicide selection.
  • Lupin growers in NSW are advised to follow the five point anthracnose management plan to prevent the disease establishing in NSW.

Seasonal conditions overview

The growing season was challenging for pulse crops during 2016. In most districts, pulse crops were sown on time following good rains in late April and early May. The onset of wet conditions from late May favoured early disease establishment. Cool and wet conditions in June and July were ideal for further disease development and spread. This allowed even low levels of disease to develop to epidemic levels. The above average rain in August and September tested many foliar fungicide programs and was a reminder of the importance of early crop protection and timely fungicide applications. Waterlogged conditions during this time also later developed into patches of stunted or dead plants later in the season. Fortunately, drier conditions in late October and November allowed pod fill to occur with low levels of pod infection.
 

Lupins

Phytophthora root rot

(also known as Sudden Death) 
This disease was widespread in southern NSW and northern Victoria in 2016. Outbreaks of the disease were driven by above average rainfall in late winter and early spring. This disease develops following a period of waterlogging (as short as 8 hours) in winter which allows the Phytophthora pathogen to infect lupin roots, and is expressed in spring when plants prematurely die often around pod filling. As the soil starts to dry out, the infected and damaged root system can no longer support the plant, leading to premature death. Occurrence of the disease is associated with soils prone to waterlogging, low lying paddocks and hardpans (which can develop perched water tables). The disease can occur on individual plants up to large patches within a crop. 

In narrow-leaf lupin, an undescribed species of Phytophthora causes the disease. In albus lupin, the disease is caused by Phytophthora cryptogea. The latter fungus is also highly pathogenic to lentils. Disease management is difficult because of the extended period of survival of the fungus in the soil. 

Management: Methods to minimise the occurrence of the disease include crop rotation and avoiding paddocks with a known waterlogging or hardpan problem.

Anthracnose

This destructive disease was detected for the first time in commercial lupin crops in NSW in 2016. Currently the disease is confined to a small number of properties in southern NSW with restrictions in place. Lupin production can continue for the remainder of NSW outside the restriction zones.  Wonga, PBA Jurien and PBA Barlock are resistant (R) whilst PBA Gunyidi (moderately resistant (MR)–R) and Mandelup (MR) are slightly more susceptible (S). All other narrow-leaf and albus lupin varieties are very susceptible to anthracnose. 

The disease is specific to lupin species only and does not affect any other pulse crops including field peas, faba beans, chickpeas or lentils. The fungus survives on infected lupin stubble and can be carried on or within infected seed, which is the main means of disease spread. Infected seed will give rise to infected seedlings the following year and initiate the disease. The fungus does not survive in the soil.

Symptoms of the disease include a distinct bending and twisting of stems into a shepherd’s crook. The bending of stems is due to the formation of lesions within the crook of the bend causing collapse down one side. Within the lesion are bright pink/orange spore masses that spread the disease within the crop. Lesions can also form on developing pods later on. Symptoms become most obvious when crops come into the reproductive phase and start flowering and podding. The disease attacks the soft plant tissue at the growing points (including stem tips, flowering spikes and pods) and works downwards into the crop canopy. Anthracnose will develop in patches or ‘hotspots’ within the crop. As the disease is spread through rain splash of spores, patches of deformed plants will form within the crop as the disease spreads following rainfall events.

A five point management plan is recommended for all lupin growers in NSW to prevent establishment and spread of the disease:
  • Treat seed for sowing with a fungicide seed treatment containing thiram.
  • Separate this year’s lupin crop away from last year’s lupin stubble.
  • Control volunteer lupins on your property.
  • Control machinery and people movement into and out of lupin crops.
  • Apply a foliar fungicide at 6-8 weeks post emergence (with a grass herbicide) using fungicides containing mancozebɸa, chlorothalonilɸb or azoxystrobinɸc, and a follow up at pre-canopy closure.

ɸaLabel states application via spray when leaves, flowers or pods show first signs of infection and weather conditions are likely to remain humid or wet. If disease pressure is severe and conditions favour spread, repeat sprays at 2-3 weeks. ɸbNot registered for anthracnose in lupins but can be used under permit number 82209. Do not apply more than two foliar applications per season with a re-treatment interval of 14 days. ɸc Not registered for anthracnose in lupins but can be used under permit number 82226. Apply up to two foliar applications per season. The first application must be applied before the disease is established and no later than the onset of flowering. A second application can be made 10-14 days after the first application.

Growers are encouraged to inspect lupin crops regularly and report any unusual disease symptoms to their nearest NSW DPI or Local Land Services (LLS) office. Early detection will prevent establishment of the disease in NSW and protect the lupins industry.

Restrictions remain in place on the movement of lupin material and machinery into NSW from SA and WA.

Faba beans

The main diseases of faba beans in southern NSW and northern Victoria are ascochyta blight (AB) (caused by Ascochyta fabae), chocolate spot (caused by Botrytis fabae and B. cinerea) and rust (caused by Uromyces viciae-fabae). These fungal pathogens have the potential to reduce crop yield and seed quality. Disease management strategies have been developed that utilise a range of chemical and non-chemical approaches such as paddock selection, crop rotation, selection of seed for sowing, variety selection, sowing date and rate, and the strategic use of foliar fungicides. At this stage, growers still rely heavily on fungicides as part of a disease management strategy and success is dependent on correct disease identification, timing of product application and fungicide choice. 

Wet conditions in 2016 were challenging for faba bean growers. Wet conditions, the logistics of applying fungicides and the sourcing of fungicide products all tested growers and advisers. 

Ascochyta blight

 This disease develops early in the growing season, especially when conditions are cool and wet for prolonged periods. Early infection results in the development of leaf lesions. These later spread and develop into stem lesions in susceptible varieties. This can cause premature lodging in susceptible varieties. Later in the season, after the commencement of flowering, the disease can spread onto developing pods and cause seed staining.

Chocolate spot 

This disease is favoured by warm, humid conditions for prolonged periods (four-five days). Typically the disease develops later in the growing season as crops commence flowering and after canopy closure. Canopy closure is an important crop growth stage and marks the point where the crop’s canopy develops from single rows within the paddock to a continual cover of canopy, which then creates a humid microclimate. Chocolate spot has the potential to develop quickly when conditions are favourable and results in pod abortion and plant damage (through leaf infection and loss of leaf tissue).

Rust

This disease can be found from mid spring and is favoured by warm temperatures (above 20°C). The disease can develop very quickly, requiring only six hours of leaf wetness for infection. Rust is not usually a problem every year in southern regions, and often occurs in years with good spring rainfall and mild temperatures.

Disease management strategy — the critical periods

There are three critical periods for monitoring faba bean crops for disease:
  • 1st critical period is five to eight weeks following emergence. Ascochyta blight is the main target at this time and the use of foliar fungicides is aimed at reducing early establishment of the disease in crop.
  • 2nd critical period is during early flowering just prior to canopy closure. This is the last opportunity to apply a fungicide that will penetrate into the crop canopy and protect potential infection sites from disease establishment and spread. Chocolate spot is the target disease at this time and treatment of this disease from becoming established under the crop canopy is essential. In varieties that are ascochyta blight susceptible, a fungicide application at this time will help prevent further spread of this disease. 
  • 3rd critical period is at the end of flowering and early pod fill. Applications of fungicide at this time should be aimed at protecting developing pods and preventing any further disease spread. The target diseases at this time are ascochyta blight, chocolate spot and rust. 

Fungicide choice

There are a number of registered foliar fungicides for use on faba bean to manage ascochyta, chocolate spot and rust. Some products are broad spectrum and are effective against both ascochyta and chocolate spot (such as products containing mancozeb and chlorothalonilɸa), while others are specific against chocolate spot (such as products containing carbendazim and procymidone). 

ɸaChlorothalonil products are registered for control of chocolate spot and rust, but not ascochyta.

Be aware that the general period of protection offered by these products is 10–14 days.

Correct disease identification is important as this will determine the choice of product. Currently registered products are listed in the NSW DPI Winter Crop Variety Sowing Guide.

Field peas

Blackspot

(also known as Ascochyta blight of field pea) 
This disease is the most common foliar disease of field peas. The disease is caused by a complex of four fungi, which between them can survive on seed, stubble and in soil. Development of the disease is favoured by cool, wet conditions in winter and spring. Symptoms of the disease include distinct round, black lesions which form on leaves, elongated round lesions which form on stems, blackening of the stem at ground level and pod lesions. The highest levels of blackspot generally form in paddocks with a recent history of field peas or paddocks sown to field peas adjacent to last year’s field pea stubble.

Damaging levels of blackspot did develop in field pea crops in southern NSW in 2016. This was often due to a number of causes including:
  • Crops sown early — this increases the exposure to early season ascospores showers from old field pea stubble and multiple infection events throughout winter.
  • Crops sown adjacent to last year’s field pea stubble — fungal inoculum can be easily blown into adjoining paddocks and initiate disease outbreaks.
  • Waterlogged crops — above average winter and spring rainfall resulted in waterlogging of some field pea crops which reduced crop vigour and increased susceptibility to blackspot.
Conditions conducive to disease  in 2016 demonstrated that even low levels of blackspot can quickly develop to epidemic levels and cause yield loss.

Management: Options include crop rotation, paddock selection away from last year’s stubble, following the recommended sowing time (avoidance of ascospore showers early in the season from old stubble), fungicide seed dressing, and foliar fungicides in high disease pressure situations.

Chickpeas

Ascochyta blight (AB)

(fungus Phoma rabiei previously called Ascochyta rabiei) 
This is the most common and damaging disease of chickpeas in Australia. In southern NSW, outbreaks of AB are generally not as severe compared to northern NSW or Victoria, where chickpeas are grown more frequently and background levels of disease inoculum are higher.

Ascochyta inoculum can be present in four forms:
  • Ascochyta infected chickpea residue being discharged out the back of headers or spread by floods and surface water.
  • Seed internally infected by the fungus (a consequence of pod infection).
  • Seed contaminated externally with infected chickpea residue during harvest and handling.
  • Volunteer chickpea plants infected over summer and autumn.
Field experiments (experiment) and extensive chickpea crop surveys (observation) conducted in northern NSW for more than 10 years have revealed a number of key strategies to manage the potential yield losses due to AB. The following will reduce the occurrence and impact of the disease in 2017 chickpea crops:
  • Grow varieties with improved AB resistance (experiment/observation). These varieties will have less disease and require fewer fungicide sprays.
  • Burn cereal stubble (this holds AB inoculum, observation). Infected chickpea residue discharged during harvest of 2016 crops blows onto paddocks that are intended for chickpeas in 2017; most of these will have had a cereal crop in 2016 (or 2015).
  • Remove volunteers (observation). Volunteer chickpea plants infected with AB will provide inoculum even if the volunteer plants are killed with herbicide. Controlling volunteers early will restrict their size and limit the amount of inoculum they can produce.
  • Treat all planting seed (experiment). Proper treatment of seed with a registered fungicide will control both internally borne AB and external contamination.
  • Sow later in planting window (experiment/observation). This reduces the number of infection events that can impact on crops.
  • Wider rows (experiment/observation). Wide rows improve airflow through the crop leading to more rapid drying after a rain event or dew. They also delay canopy closure and improve penetration of fungicides later in the season.
  • Tyne openers rather than disc (observation). 2016 observations of less AB where crops had been sown with tynes is thought to reflect burial and movement of Ascochyta inoculum away from the emerging seedlings.
  • Fungicide before first post emergent rain event (experiment/observation). 2016 crops that had an early preventative Ascochyta fungicide had less disease than crops that were not sprayed until after the disease was detected. 

All pulses

Sclerotinia stem rot

Many pulse crops in southern NSW and northern Victoria developed symptoms of Sclerotinia rot in 2016. Affected crops included lupins, chickpeas, field peas and faba beans. The type and severity of damage varied depending on the crop and paddock circumstances.

For sclerotinia to develop, three factors have to coincide:
  • The host crop has to be at a susceptible growth stage. Often pulse crops with a large crop canopy are more prone to developing Sclerotinia as moisture is retained within the canopy for longer periods. For some pulse crops, the susceptibility to Sclerotinia increases as flowering commences.
  • Environmental conditions have to be favourable for the pathogen to develop. Sclerotinia rot requires ample rainfall in winter to soften soil-borne sclerotia and allow development of apothecia, the fruiting structure of the fungus that releases ascospores. Further rainfall is also required in winter and spring to supply ample canopy leaf wetness for infection of plants by ascospores.
  • The disease has to be present. In the case of Sclerotinia, this means sclerotia have to be present in the paddock. Past Sclerotinia outbreaks and cropping history can be a good indicator — in particular, consider the frequency of canola in the rotation.
Unfortunately, there are few post emergent management options for Sclerotinia in pulse crops. There are no foliar fungicidesɸ currently registered to manage the disease, so effective management relies on pre-sowing strategies. These strategies include:
  • Do not be tempted to sow pulse crops outside the recommended sowing window. Past observations on field experiments at Wagga Wagga have indicated that early sown pulse crops such as field peas and chickpeas are more prone to developing Sclerotinia infection compared to sowing at the recommended time.
  • Consider past cropping history, in particular canola. Canola is an excellent host for the Sclerotinia fungus and can build up sclerotia numbers quickly in the soil. The same sclerotia can release spores that also infect pulse crops. Try and decrease the frequency of Sclerotinia host crops in the rotation, in particular canola. Avoid planting consecutive broadleaf crops.
  • Pulse crops with a heavy, dense crop canopy are more prone to developing the disease. Follow recommended sowing rates for your district.
  • Wider row spacings can be a useful strategy by increasing airflow through the crop canopy and delaying canopy closure. However, be aware that early sowing can negate any benefits. 
  • Make note of outbreaks of Sclerotinia and identify those paddocks or properties as a disease risk. Sclerotia can easily survive in the soil for at least five years and can pose a risk for following crops. One bad sclerotinia outbreak can be a five year headache.

ɸProcymidone is registered for control of sclerotinia in navy beans but these are not commonly grown in this region.

Hardpans and waterlogging 

Many pulse crops in southern NSW and northern Victoria had symptoms of waterlogging in 2016. Throughout spring, many plant samples were received at the diagnostic laboratory at Wagga Wagga with evidence of waterlogging, leading to premature death. 

Waterlogging can have a three stage effect on pulse crops. Firstly, plants standing in free water can effectively ‘drown’ if the waterlogged conditions occur over an extended period and the pulse crop will die prematurely. Secondly, waterlogged conditions can promote root pathogens to infect and cause injury, such as Phytophthora, which are expressed later in the season. Thirdly, observations in northern NSW chickpea trials and crops since 2010 have consistently shown that resistance to foliar disease is reduced if plants are waterlogged. Thus, managing AB in PBA HatTrick (rated MR) is challenging in areas of crops that have been stressed from waterlogging. Indeed, some northern growers had difficulty controlling Ascochyta in waterlogged PBA HatTrick crops using fungicide strategies that worked in non-waterlogged crops.

Hardpans (or ploughpans) can lead to waterlogging issues, in particular the development of perched watertables in the root zone. Hardpans often form just below the depth of cultivation. This can result in root disease development, poor nodulation or poor root growth. In the 1990s, a survey of pulse crops in southern NSW found 50% of paddocks to have soil bulk densities high enough to limit water movement and root development in pulse crops.  

Check paddocks to be sown to pulses for hardpan layers. It may be necessary to cultivate paddocks at a deeper level or use ripping tynes to break up layers.

Useful resources

NSW DPI Winter Crop Variety Sowing Guide (disease updates, variety resistance, fungicide products).

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. 

Contact details 

Kurt Lindbeck
NSW Department of Primary Industries, Wagga Wagga Agricultural Institute 
02 69 381 608
kurt.lindbeck@dpi.nsw.gov.au

GRDC Project code: DAN00177