Ascochyta Blight of Lentil

Note Number: AG1350
Published: May 2006
Updated: May 2009

 

This Agnote provides Victorian grain growers with information on the integrated management of Ascochyta blight of lentils.

Ascochyta Blight in Victoria

Ascochyta blight is a serious disease of Victorian lentil crops. The disease is favoured by periods of high spring rainfall or when there are prolonged wet periods. While the disease can cause leaf abscission, it can also discolour seed which can result in the downgrading of seed quality. 

What to look for

All above ground plant parts of lentil plants can be affected by ascochyta blight. Symptoms may appear on plants from the seedling to mature stages. The disease appears as spot-like lesions which are initially light grey, but become tan with a dark brown margin (Figure 1). The centres of lesions become speckled with pycnidia (tiny, dark fruiting bodies). The presence of pycnidia is the best way of identifying ascochyta blight lesions from those caused by other diseases such as botrytis grey mould or stemphylium blight. Heavy infestations of ascochyta blight will cause premature leaflet drop and stem dieback at the growing tips giving plants a blighted appearance.

Pod infection can lead to seed infection and discolouration of the grain (Figure 2 & 3). Infected seed generally has brown patches on the seed surface, but may show no symptoms at all. Compared to healthy seed, heavily infected seed is purplish-brown, shrivelled and reduced in size (Figure 3).

Economic Importance

Ascochyta blight has the potential to occur in all areas where lentils are grown. Serious yield losses due to the disease are unlikely, but seed discoloured due to pod infection by the pathogen can significantly reduce the market value of the grain. This is very important if choosing to grow green lentils for the whole seed market.

Disease Cycle

The fungal pathogen Ascochyta lentis that causes ascochyta blight can survive in infected seed, and in previously infected lentil stubble.

Seed can remain infected for several years. Sowing infected seed can give rise to infected seedlings, and the appearance of symptoms at the seedling stage. 

Previously infected stubble is an important source of fungal inoculum. Spores are produced on old stubble and are spread to plants by rain splash. Further spread from plant to plant within crops then occurs through rain splash. Cool, wet weather with frequent rainfall promotes sporulation, spore dispersal and infection. The development of ascochyta blight epidemics is largely determined by the prevailing environmental conditions, especially the presence of moisture.

Management

Clean Seed. 

Using old or damaged seed can reduce seedling vigour and increase susceptibility to infection. Only sow seed with less than 5 per cent Ascochyta infection, and preferably use seed with nil infection.

Resistant varieties

Use varieties with greatest resistance. Currently the varieties Northfield, Nipper, Boomer and Nugget have useful levels of resistance to this disease, as do Aldinga, Matilda and Digger.

Paddock Selection

Infected crop residues can harbour Ascochyta lentis, the causal agent of ascochyta blight. Therefore, avoid planting this seasons crop near old lentil stubble. A program of stubble reduction may also be undertaken by grazing, burning or burying to reduce the carryover of infected stubble into the following season. Allow a break of at least 3 years between lentil crops.

Seed Treatment

Use a registered seed treatment for the control of seed-borne diseases in lentil. Seed treatments can have a deleterious effect on rhizobia. Therefore, seed should be treated with fungicide and then inoculated with rhizobia in two separate operations. Rhizobia should be applied to seed immediately before sowing, especially on acid soils.

Time of Sowing

Early sowing encourages early infection and increased levels of the disease. Follow the recommended sowing dates for your district.

Foliar Fungicides

In areas of high risk it may be necessary to apply foliar fungicides to protect crops, especially if a susceptible variety is grown. Use a fungicide product registered for this use or obtain professional advice about other possible options. It is worth remembering that fungicides are protectants and are most effective if applied before disease development.

Fungicides should be applied according to label directions for use, ensuring the key points of spray timing and frequency are observed as well as grazing and harvest withholding periods.

Further References

More detailed information can be obtained from the DPI Information Note Series: 

Seed Health Testing in Pulse Crops (AG1250)
Victorian Winter Crop Summary (2009)
Lentil Management Strategy for Southern Region. Pulse Australia
Pulse Seed Treatments and Foliar Fungicides (SARDI)
Winter Pulse Disorders (2002) The Ute Guide.

Contact/Services available from DPI

DPI Field Crops Pathology, Grains Innovation Park, 110 Natimuk Rd, Horsham 3400. Tel (03) 5362 2111, or the DPI Customer Service Centre 136 186.

Acknowledgements

This Agnote was developed by Kurt Lindbeck, May 2006 and was reviewed by Helen Richardson and Frank Henry, BioSciences Research - Farm Services Victoria, May 2009.  Financial support by the GRDC is gratefully acknowledged.