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Agronomy update: Sclerotinia white mould impacts on lentil

Sclerotinia white mould, caused by the fungus Sclerotinia sclerotiorum, and Botrytis grey mould, caused by the fungus Botrytis cinerea, can impact lentil production in wetter areas of the Prairies. However, the susceptibility of lentil to these diseases was unknown in Alberta prior to a research study being conducted in Lethbridge, Alta. 

The objectives of this study, led by Syama Chatterton with Agriculture and Agri-Food Canada, were to determine cultivar responses to Sclerotinia white mould and Botrytis grey mould in irrigated and dryland conditions and variable disease pressure, and the influence of plant density on disease pressure. 

Field trials were conducted from 2013 to 2015 at the Agriculture and Agri-Food Canada Lethbridge Research and Development Centre, Alberta. Ten lentil cultivars from five market classes were planted at either 12 or 16 seeds per square foot (120 and 160 plants/m2) under irrigation and dryland plots. The ten lentil varieties, provided by the Crop Development Centre (CDC), University of Saskatchewan were CDC Dazil, CDC Imax, CDC Imigreen, CDC Impact, CDC Impala, CDC Imperial, CDC Impower, CDC Improve, CDC Imvincible and CDC Maxim. Irrigation was applied starting in early July, with 0.6 inches (1.5 cm) applied three times per week, unless there was a rain event. 

Total precipitation was above average in 2013 at 11 inches (281 mm) and also above average in 2014 at 11.4 inches (290 mm) but below average in 2015 with 4.2 inches (106 mm), compared to the 30 year average of 8.5 inches (215 mm).

Sclerotinia white mould incidence varied significantly between varieties under irrigated and dryland conditions, but there was no consistent trend in variety performance. Under irrigation, Sclerotinia white mould incidence was highest in 2013 at up to 87 per cent incidence with less severe incidence in 2014, and less than eight per cent incidence in 2015. Under dryland, incidence was the highest in 2013, but still less than 25 per cent, and negligible in 2014 and 2015. 

Planting density did not significantly affect Sclerotinia white mould incidence under irrigated or dryland conditions.

Botrytis grey mould incidence was similar across the cultivars. Under dryland conditions, the disease was almost undetectable at either planting density. 

Under irrigation, Botrytis grey mould was highest in 2015 at 22 per cent incidence in the 16 seeds per square foot (seeds/ft²) seeding rate, and 15 per cent incidence at the lower seeding rate. In 2014, incidence was 10.6 per cent with the low seeding rate and 8.4 per cent at the higher seeding rate. In 2013, very low disease was observed. Botrytis grey mould incidence was also significantly higher at the 16 seeds/ft² planting density compared to 12 seeds/ft². 

Lentil yield under dryland conditions were usually significantly higher than irrigated conditions. Other research in Alberta has found that precipitation levels of six to 10 inches (150 to 250 mm) during the growing season produce maximum yield, and these conditions were present in the 2013 and 2014 dryland trials. 

The highest lentil yields were generally on dryland plots with a seeding density of 16 seeds/ft². For example, in 2014, the dryland plots planted with 16 seeds/ft² yielded 1709 pounds per acre (1920 kg/ha) compared to 1554 lbs/ac (1746 kg/ha) at the 12 seeds/ft² seeding rate. These yields compared to an irrigated yield of 990 lbs/ac (1112 kg/ha) at the 12 seeds/ft² rate and 905 lbs/ac (1017 kg/ha) at the 16 seeds/ft² rate in 2014.

Overall, lentil yield was significantly higher at a density of 16 plants/ft² compared with 12 plants/ft² except in 2013 and 2014 under irrigated conditions. The lower irrigated lentil yields in 2013 and 2014 were likely due to the high levels of Sclerotinia white mould in the plots. 

The results of the study showed that Sclerotinia white mould may be a limiting factor in wetter and cooler areas of the Prairies. While there were differences in lentil variety susceptibility to Sclerotinia white mould, it was not consistent across the years, possibly due to differences in the growing seasons between the years. The varieties showed moderate to high susceptibility to Sclerotinia white mould, and would not be suitable for areas where the disease is present in wetter areas.

Other research at the University of Saskatchewan found that leaves, stems, pods and flowers can all be infected by S. sclerotiorum. Lentil plants older than six weeks were found to be more susceptible, and may be why wet weather later in the season can cause more Sclerotinia stem rot.

Similarly, Botrytis grey mould may be a problem in dense stands that are lodged due to wet and cool weather. 

Foliar fungicides are registered for control or suppression of both diseases. Application timing is usually at the first sign of disease, or around the beginning of flowering before the onset of the disease, depending on the product.  

Bruce Barker divides his time between CanadianAgronomist.ca and as Western Field Editor for Top Crop Manager. CanadianAgronomist.ca translates research into agronomic knowledge that agronomists and farmers can use to grow better crops. Read the full Research Insight at CanadianAgronomist.ca.