Ascochyta blight

Phoma rabiei (chickpeas), Ascochyta fabae f.sp. fabae (faba beans), Ascochyta fabae f.sp. lentis (lentils), Ascochyta pisi (field peas)

Ascochyta blight (AB), commonly referred to as ascochyta, is a serious fungal disease which affects pulse crops including chickpeas, faba beans, lentils and field peas. The disease has a specific strain for each pulse crop and can’t be spread between them.

In faba beans, Ascochyta fabae is sometimes confused with more minor, non-yield limiting diseases alternaria leaf spot and cercospora leaf spot, whereas in favourable conditions, AB can cause yield losses in faba beans of 10 – 30 per cent. In lentils, it can be misidentified as botrytis or stemphylium blight, however AB contains pycnidia in the lesions while these other diseases do not. In all crops, AB can cause both yield losses and quality downgrades as a result of the disease discolouring the grain. In field peas, AB is also referred to as blackspot.

Refer to the link below for more detailed information on ascochyta in field peas.

Description

In chickpeas, AB symptoms are usually first observed as the wilting of individual or small groups of seedlings; collectively they can appear as if they have ‘hayed-off’ prematurely. Leaf lesions usually begin as pale green-yellow patches before developing into small, round lesions with concentric circles of brown to black spots (pycnidia) with dark brown margins. These pycnidia are specific to AB. On the stems, the lesions are oval-shaped, brown in colour and contain pycnidia. As the lesions develop, they can cause girdling. Lesions can also occur on pods; these look similar to leaf lesions.

P. rabiei survives between seasons on infected stubble, seed and volunteer chickpea plants. P. rabiei only needs three hours of leaf wetness and while it can develop between 5 - 30 °C, it develops fastest when temperatures are between 15 - 25 °C and the humidity is high.

In faba beans, symptoms are also commonly observed early in the growing season where they first appear as small dark brown spots, which can be confused with chocolate spot, before changing to become grey. These grey spots also develop on the stems and pods and when they enlarge, they develop grey centres which contain pycnidia. The centres of these lesions may also fall out, leaving a shot-hole appearance. In contrast, alternaria spots have a red-brown margin and contain concentric rings but do not contain pycnidia while cercospora spots are darker with irregular edges and the spots also do not contain pycnidia.

In lentils, symptoms can be seen at all growth stages and appear as light grey spots before becoming tan with a brown margin. The centres of these spots also contain pycnidia. Pod lesions are similar to leaf symptoms. Under high disease pressure, lentil crops infected with AB will have premature leaflet drop and stem die-back at the growing point.

Ascochyta spp. survives between seasons when infected seed is sown, or from infected stubble, where it can survive for several years. Disease development can occur at any plant growth stage and is favoured by cool, wet conditions.

Control

Management of ascochyta in pulses requires an integrated approach using cultural methods and registered fungicides. The following practices are recommended to manage the risk of ascochyta;

Rotate crops to allow spores on the soil or crop residue to lose viability
Plant pulses in paddocks after a two-year break in faba beans and a three-year break in chickpea, lentil and field pea crops
Remove or bury contaminated trash residue, taking care to minimise wind erosion risks
Sow clean seed
Control alternative hosts
Plant more tolerant varieties
Use a registered seed treatment
Inspect regularly to identify disease symptoms early
Apply foliar fungicides in areas of high risk.

AB can easily be spread through spore transfer via clothing, people, machinery, vehicles and animals; therefore, if it is detected, ensure all machinery and clothing is washed, disinfected and removed of soil material before inspecting other crops.

Aviator® Xpro is registered for the control of ascochyta blight in chickpeas, faba beans, field peas and lentils and should be applied preventatively before an infection event occurs (i.e. before rain). It should also be applied as a part of a preventative program in rotation with other registered fungicides from different mode of action groups.

Related Pests

Blackspot of field peas

Mycosphaerella pinodes, Phoma mediccaginis var. pinodella, Phoma koolunga, Ascochyta pisi

Commonly referred to as ascochyta blight, blackspot is one of the most serious diseases of field peas and is widespread in Victoria and South Australia. In field peas, blackspot is produced by four different pathogens, producing symptoms that are indistinguishable from each other. Yield losses of up to 60 per cent have been reported, particularly in wet seasons.

Refer to links below for more information on blackspot in other crops.

References

Agriculture Victoria (2016), ‘Ascochyta blight of lentil’, http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/plant-diseases/grains-pulses-and-cereals/ascochyta-blight-of-lentil

Agriculture Victoria (2016), ‘Blackspot of Field Peas’, http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/plant-diseases/grains-pulses-and-cereals/ascochyta-blight-of-field-peas#

CropPro (2014), ‘Ascochyta blight of chickpeas', http://www.croppro.com.au/crop_disease_manual/ch05s02.php

CropPro (2014), ‘Ascochyta blight of faba beans’, http://www.croppro.com.au/crop_disease_manual/ch06s03.php

CropPro (2014), ‘Ascochyta of lentils’, http://www.croppro.com.au/crop_disease_manual/ch08s02.php

Galloway, J (2017), ‘Faba bean: Ascochyta blight diseases, Department of Primary Industry and Regional Development (DPIRD), https://www.agric.wa.gov.au/faba-beans/faba-bean-ascochyta-blight-disease

Moore, K, Ryley, M, Cumming, G and Jenkins, L (2015), ‘Chickpea: Ascochyta blight management, Australia Pulse Bulletin, http://www.pulseaus.com.au/growing-pulses/bmp/chickpea/ascochyta-blight

Richardson, H (2016), ‘Ascochyta Leaf and Pod Spot of Faba bean’, Agriculture Victoria, http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/plant-diseases/grains-pulses-and-cereals/ascochyta-blight-of-faba-bean