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Botrytis Grey Mould of Lentil

Note Number: AG1275
Published: June 2008
Updated: August 2012

 

Botrytis grey mould is a serious, but sporadic disease of lentil in Australia. The disease is capable of causing serious yield losses in years when spring rainfall is high and/or when there are prolonged wet periods. An integrated approach to managing the disease will minimise yield losses.

What to look for

All aboveground plant parts of lentil can be affected by botrytis grey mould. Symptoms may initially appear either on flowers and pods, or lower in the crop canopy, depending on the location of the crop. The most damaging symptoms become apparent after the crop has reached canopy closure, and a humid microclimate is produced under the crop canopy. The disease appears as discrete cream coloured lesions on lower leaves. These enlarge and coalesce to infect whole leaflets which later senesce, and fall to the ground. Unlike ascochyta blight, no small black fruiting bodies (pycnidia) can be seen within the lesions.

If conditions remain conductive for disease, that is warm and wet under the crop canopy for at least 4 days, infection can spread to the lower stems. When that happens, lesions will girdle the stem and the stem will become covered with a furry layer of grey mould. This eventually causes stem death, and the whole plant dies. Often occurring before the onset of flowering and pod fill, infection will continue to spread, resulting in patches of dead plants within crops (Figure 1).

Fig 1. A lentil crop with advanced botrytis grey mould. Note the dead patches of plants.	Fig 2. A lentil pod infected by Botrytis cinerea. The grey mouldy growth is typical of this disease.

Pods which become infected will be covered in a grey mouldy growth, will rot and turn brown when dried out (Figure 2). Seeds within these pods fail to fill properly and are often discoloured and shrivelled. When infected seeds are sown seedling blight can occur. Seedling blight is characterised by the appearance of grey mycelium growth on the stem at the soil line.

Disease Cycle

The fungal pathogens Botrytis cinerea and Botrytis fabae that cause botrytis grey mould can survive as several forms, these include infected seed, sclerotia in the soil or in infected trash (Figure 3) and on alternate host plants. Botrytis cinerea and B. fabae have a broad host range collectively, including faba bean, chickpea, field pea, lupin and pasture legumes such as lucerne and clover. Other host species include a wide range of ornamental and horticultural crops.

Sowing botrytis infected seed can give rise to infected seedlings reducing seedling survival and crop establishment. Old infected trash is an important source of fungal inoculum. Spores are produced on old trash and are carried by the wind into new crops where infection can occur. Under favourable conditions of high humidity and moderate temperatures, the disease can spread rapidly; producing spores on newly infected tissue, and further spreading the disease within crops. The development of botrytis grey mould epidemics is largely determined by the prevailing environmental conditions, especially the presence of moisture.

Environmental conditions and canopy density are primary factors that influence the development of botrytis grey mould epidemics in lentil crops. The formation of a favourable microclimate under the crop canopy, especially following canopy closure and humid conditions after rain, favour the development and further dispersal of the botrytis grey mould pathogens.

Fig 3. Lentil stems with advanced infection by Botrytis cinerea.  Note the formation of sclerotia by the fungus for survival.

Economic Importance

Botrytis grey mould has the potential to occur in all areas where lentils are grown, depending on the season, but is more common in districts with rainfall >400mm. Losses due to the disease can range from minor to very serious, depending on the variety grown, location of the crop, time of infection and amount of spring rainfall. Unprotected crops can lose up to 30 per cent of yield. In addition, seed can be discoloured due to pod infection by the pathogens, which can further reduce market value of the crop.

Management

Before sowing

Use clean seed

Only use seed with less than 5 per cent botrytis infection or preferably use seed with nil infection. Using old or damaged seed can reduce seedling vigour and increase susceptibility to infection. See the DPI Information Note: Seed Health Testing in Pulse Crops (AG1250) for more information.

Varietal resistance

Use varieties with the greater resistance to botrytis grey mould. Warning – all varieties are susceptible to grey mould in areas and years where disease pressure is high.

Paddock selection

Avoid planting this season’s crop near old lentil, faba bean, chickpea, vetch or lathyrus stubble. These crop residues can harbour Botrytis fabae or Botrytis cinerea, the causal agents of botrytis grey mould. A program of stubble reduction may also be undertaken by grazing or burying to reduce the carryover of infected stubble into the following season.

Allow a break of at least 3 years between lentil crops.

At sowing

Seed treatment

Use a registered seed treatment for the control of seed-borne diseases in lentil. Seed treatments will 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.

Sowing

Sow later and reduce seeding rates. Early sowing and high sowing rates can cause rank crop growth, lodging and increased risk of grey mould. Follow the recommended sowing rates and sowing dates for your district.

After sowing

Use foliar fungicides

In areas of high risk it may be necessary to apply foliar fungicides to protect the crop, especially if a susceptible variety is being grown. Fungicides should be applied before canopy closure for best results. If conducive (warm and wet) conditions continue follow up sprays may be necessary 12 - 14 days later.

There are a range of fungicides available to control Botrytis, and selection of the most appropriate fungicide could depend on the level of disease pressure present. Fungicides containing mancozeb, chlorothalonil, carbendazim, or procymidone have activity against Botrytis. If disease pressure is high then carbendazim or procymidone are the preferred fungicides. It is worth remembering that these products are protectants and are most effective if applied before disease development. Always check the withholding period before applying chemicals.

Further references

Pulse Australia
National Variety Trials
Victorian Winter Crop Summary
Winter Pulse Disorders: The Ute Guide
Seed Health Testing in Pulse Crops (AG1250)
Pulse Seed Treatments and Foliar Fungicides

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 Information Note was originally written by Helen Richardson and Kurt Lindbeck. It was reviewed by Helen Richardson and Frank Henry, Farm Services Victoria - BioSciences Research, June 2010 and August 2012. Financial support by the GRDC is gratefully acknowledged.