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Controlling Botrytis grey mould in lentil

Botrytis grey mould doesn’t share the same limelight as Anthracnose or Ascochyta blight, but it can be an occasional foliar disease in lentil. Limited research has been conducted on foliar fungicide application timing, but one study found that a single application of boscalid (Lance) at early- or mid-flower, depending on seeding date, could be effective in controlling the disease. 

Botrytis grey mould is caused by Botrytis cinereal. It most commonly develops under cool and wet conditions later in the summer, especially in dense plant stands. The disease causes stem and pod rot during flowering and seed filling, resulting in economic losses. 

Symptoms typically first appear at mid- to late-flowering. The infected stem is light brown or bleached, and develops a grey, mouldy appearance. 

Infected pods turn brown, do not fill properly, and can also develop a grey, mouldy appearance. Seed from infected pods are shriveled and discoloured. Dead flower petals are often a source of infection because B. cinereal colonize on dead tissue first, resulting in infections of pods that are in contact with the dead petals.

The disease can spread from plant to plant in dense, lodged stands, resulting in the development of the disease in patches in the field. The grey, mouldy growth contains spore-bearing structures and spores. When disturbed, grey clouds of spores are released to spread further across the field.

The pathogen is both seed- and stubble-borne, but seedling blight caused by the pathogen may not be related to disease development in maturing plants. Rather, Botrytis grey mould is more likely caused by spores that are spread by the wind from infected stubble. 

Disease surveys over the past decade have found that Botrytis grey mould varies from year to year, much like with other foliar diseases. The Saskatchewan Ministry of Agriculture conducts annual disease surveys, and have found that Botrytis grey mould prevalence has range from a zero in several years to a high of 66 per cent of fields surveyed in 2016. 

Even though seed-borne B. cinereal may not cause Botrytis grey mould in later crop stages, using disease-free seed and a seed treatment may still help avoid seedling blight that is caused by the pathogen. 

Several foliar fungicides are registered for control of Botrytis grey mould. Research at the University of Saskatchewan, led by professor Sabine Banniza with the Crop Development Centre, looked specifically at foliar application of Lance (boscalid) fungicide for control of Botrytis grey mould in lentil. It is one of the few published studies to look at the timing of foliar fungicide application in lentil. 

The research was conducted at two sites at Saskatoon and Outlook in 2002 and 2003, and was published in the Canadian Journal of Plant Pathology in 2021. Two seeding dates were compared with early seeding around mid-May, and late seeding during the first week of June. All experiments were inoculated with B. cinereal. 

Lance fungicide application timings were assessed comparing one application at early flower, one at early to mid-flower, one application at late flower, plus two applications at early plus mid-flower, two applications at early plus late flower, two applications at mid-flower plus late-flower, and three applications at early plus mid-flower plus late-flower. 

Unfortunately, disease pressure was insufficient in 2003, so the results of the research are based on the one year when disease pressures were moderate. In control plots, early season disease severity at both locations was 55 per cent in the control plots, and was 33 per cent in late-seeded Saskatoon plots, and 39 per cent in Outlook late seeded plots.

Under these moderate disease pressures, the researchers concluded that “a single application at mid-flower in early seeded experiments and at early flower in late-seeded experiments was as efficacious as a double or triple application of boscalid.”

These findings are similar to label guidelines for other foliar fungicides now registered in Western Canada for control of Botrytis grey mould in lentil. Delaro, Seranade OPTI, and Vertisan labels recommend (depending on the product) to apply prior to, at the first sign, or at early flowering. These products, as well as Lance, bring the added benefit of controlling other foliar diseases, such as Ascochyta blight or Anthracnose or Sclerotinia stem and pod rot. 

Perhaps another way of looking at Botrytis grey mould control is that foliar applications to control other foliar lentil diseases that are usually more prevalent may also be controlling Botrytis grey mould as a bonus. And that’s perhaps why the disease isn’t front and centre in lentil growers’ minds. 

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.