Identifying and Managing Lentil Diseases (Summer 2017 PCN) JUL 7 2017 | Producers | Pulse Crop News
Neil Whatley, Alberta Agriculture and Forestry
The main cause of lentil foliar diseases is environmental conditions. Unless the growing season is uncharacteristically wet, foliar disease is not a serious concern for lentil producers; however, a sound crop rotation is also critical. Extra diligence when growing lentil in the traditionally wetter Black and Gray soil zones is important.
Disease resistance for specific diseases continues to be bred into the newer lentil varieties. Almost all lentil varieties now have good resistance to ascochyta blight, historically the most problematic lentil disease on the Prairies. Thus, seeing ascochyta disease symptoms on most varieties is improbable. If you are unsure about the ascochyta blight resistance of a variety being grown, check the provincial seed guide.
Newer lentil varieties have fair to good resistance to anthracnose, however, even those with the ‘good’ designation only have resistance to one of the two genetic races that control anthracnose. Anthracnose symptoms will emerge as air temperatures warm up if the humidity in the crop canopy is heightened by additional precipitation in June and July. Visible
symptoms begin in the lower plant canopy affecting the stem, branches and leaflets before spreading upward to eventually affect pods. A typical anthracnose symptom on the stem and branches is a sunken cream to tan coloured lesion surrounded by a dark brown border, leaving a series of
cankers on the lower stem. Infected lower leaflets have yellow to brown coloured lesions on their surface and eventually drop to the soil. If precipitation persists, distinct yellow patches of infected plants form and expand amidst an otherwise green field.
If there’s considerable precipitation in a maturing lentil crop that encourages excessive vegetative growth and lodging, sclerotinia white mould may develop later. Lentil crops are vulnerable to
sclerotinia when grown in rotation with other susceptible crops like canola, mustard, sunflower and field pea. This is one reason why lentil does better in rotation with a cereal crop. Characteristic sclerotinia symptoms are white bleaching of plant tissues and cottony white mould growth on diseased leaves and stems.
Although less common, botrytis grey mould and stemphylium blight symptoms may develop later in the growing season if there’s mid to late season precipitation. When the crop canopy is denser and lodges from a wet, cool summer, botrytis causes stem and pod rot during the flowering and seed filling stages. Pods fail to fill and large patches of diseased plants can spread, similar to patches of anthracnose infection.
Developing later in a wet growing season, stemphylium blight symptoms begin as small, yellow coloured lesions on lentil leaflets, which coalesce into larger yellow lesions if wet weather continues, leading to leaf drop. It is currently thought that stemphylium assists with natural vegetation desiccation in preparation for lentil harvest, however, current research is investigating
whether yield can be compromised.
Since all of these foliar fungal diseases flourish under environmental conditions of higher humidity, they can be worse when using higher seeding rates and when lentil is grown under irrigation or in higher rainfall regions.
Although a fungicide application is not always warranted, several fungicides are registered to control foliar lentil diseases. Anthracnose is the most yield limiting disease at this time, so scouting for anthracnose should begin at the 8 to 10 node stage of the lentil plant, just prior to the canopy closure and flowering period. Begin by observing the higher risk areas of the field like low areas where humidity accumulates, but also check mid-slopes. Pull the canopy back and search for evidence of the small brown anthracnose spots developing on the lower part of
the stem. Under humid conditions, spots rapidly expand into lesions. Since anthracnose disease development progresses from the bottom to the top of the plant, the most critical period to stop or slow anthracnose disease development with a fungicide application is at the 9 to 10 node stage or early flowering period, prior to canopy closure. If conditions favouring the disease persist, an additional fungicide application to protect new plant growth may be necessary 10 days later. However, canopy penetration may be limited and ensure a different fungicide mode of action is used the second time to prevent pathogen resistance.
If wet environmental conditions persist after canopy closure, the lentil crop may be susceptible to sclerotinia infection, which can be a challenge to control with fungicides. A fungicide control measure must be made prior to seeing sclerotinia symptoms. So, if sclerotinia is anticipated due to lentil being grown on canola stubble, for example, an early infection that occurs shortly after canopy closure may be controlled with a fungicide application, however, a late season infection, which usually occurs at the base of a dense canopy, may be uncontrollable.