Anthracnose, caused by the fungus Colletotrichum truncatum, is a serious disease of lentil. Yield losses of 60-70% have been reported. The disease is widespread in southern Manitoba and has been spreading in Saskatchewan in recent years.
Appearance: the onset of disease usually is associated with the development of a crop canopy dense enough to retain moisture underneath. White to gray or cream-coloured spots develop on leaflets. These spots enlarge resulting in dieback and abscission of leaflets. There are also spots on the stems that are tan to golden brown in colour. They appear first at the base of the stem, move up the plant and coalesce rapidly, thus causing dieback.
Disease Cycle: Anthracnose is both a stubble and seed-born disease. Levels of seed infection are usually very low (2%). Spores of the pathogen are spread mainly by rain-splash. Warm wet weather contributes to disease epidemics.
a) Use disease-free seed – Although the disease is not highly seed-born, it is important not to introduce a new contamination of the disease to your farm via infected seed. Seed treatments can be used for seed-borne infections of this disease.
b) Crop rotation – Avoid planting lentil, peas or faba beans in a rotation more than once every 4 or 5 years.
c) Apply registered fungicides prior to flowering, and repeat if conditions for disease development are favorable. More than one application may be necessary, if it is starting as flowering begins.
The first symptoms of anthracnose may appear on seedling leaflets. Although this is weeks before a fungicide should be applied, these early symptoms provide a warning that spraying may be necessary. Not everyone can identify the early symptoms and they may be confused with symptoms of ascochyta blight and stemphylium blight, or even with environmental damage, such as herbicide injury. To help you identify the early symptoms of Anthracnose Discovery Seed Labs has developed a kit. This kit is designed to help growers obtain an accurate identification of suspicious symptoms on lentil leaflets within 48 hours of collection. Please follow the instructions carefully.
1. At any stage from two weeks after emergence, search your field for leaflet symptoms is similar to those described above. Remember that these are typical examples and symptoms in nature are not always typical. The best time to begin searching will depend on the weather: generally there is no point searching until 6-8 days after rainfall on the emerged plants. Concentrate your search in the field where the stand is denser (often low spots), on lower leaves, and along edges of the field next to where lentil was grown in recent years.
2. Open the collecting dish and moisten the blotting paper inside with clean (preferably distilled or bottled) water. Do this before you go to the field to collect leaflets. Moisten the paper thoroughly (you may need to add water twice), but ensure that there is no excess water in the dish.
3. Collect 15-20 leaflets with suspicious symptoms from the field. Spread them out on the surface of the moist filter paper in the dish. Make sure that you keep the leaflets clean and do not introduce soil into the dish. You will probably find that this is easier if you use a pair of forceps (tweezers) to pick the leaflets. HINT 1: Do not collect bundles of plants in the field, put them in the back of your truck, and drive home before trying to pick off leaflets with symptoms. You will probably find that all the diseased leaflets have blown away. HINT 2: This job will be easier if you go to the field with a partner!
4. Seal the lid of the dish to the bottom with a ring of masking tape around the edge.
5. Label the dish with your name, telephone number, the location of the field, and the date and time of collection.
6. Wrap your dish or dishes carefully to prevent breakage and send by bus or courier to Discover Seed Labs. Plan for the shipment to arrive within 48 hours and on a working day. If shipping will be delayed, store in a refrigerator. You must enclose an identification fee of $ per sample/dish to receive a result.
7. At Discovery Seed Labs we will examine the leaflets microscopically for evidence of the anthracnose fungus and report the same day by telephone.
8. Remember that the results reported will be “yes” or “no”, not quantitative. A “yes” answer does not imply that spraying is necessary and a “no” answer does not guarantee that anthracnose will not appear later in the crop. If the answer is “no”, you may wish to make a second collection of leaflets with suspicious lesions later.