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| Wednesday, January 03, 2007 |
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Frequently Asked Questions - Identification and Management of Lentil Diseases Which
Diseases are Important in Lentils? To get an answer to your own question, click here
Which diseases are important in lentils in Saskatchewan? Ascochyta blight and anthracnose are the two most important diseases followed by botrytis stem and pod blight. These diseases become most problematic from flowering to maturity. Sclerotinia is also widespread but not economically important, except where lodging due to wet conditions occur. If I use a resistant variety, do I need to spray? Lentil varieties classified as “resistant” are not completely immune to the diseases. These varieties resist infection and damage to a reasonable extent and under certain conditions the crop may show few symptoms and suffer little damage. However, if conditions are favourable for disease development and spread, the crop may succumb to the pressure and suffer significant damage. Hence, fungicide application may be needed to assist the plant and control the disease. What are the symptoms of these diseases and when do they appear? Ascochyta: Grey to tan spots or lesions on leaflets, stems, flowers and pods, with dark margins and often with tiny black fruiting bodies (pycnidia) in the centers (Fig. 1). Lesions first
appear on lower leaflets close to soil surface and spread up the plant canopy. Lesions on stems can girdle the plant resulting in wilting. Leaves may turn brown and die off. Anthracnose: White to grey or cream-colored spots on leaflets and stems (Fig. 2). First appear on lower leaves and stem and
move up the canopy. Leaves and entire plants may die back and stems of mature and dead plants often blacken. Leaflets litter soil surface. Leaf symptoms appear between 8 & 12 node stages – approximately one week before flowering. Lesions on stems can girdle the plant resulting in wilting. Yellow patches appear in fields and enlarge asthe disease spreads and plants die. Botrytis: Infected seeds produce infected seedlings which die soon after emergence, resulting in reduced plant density. For the rest of the crop, symptoms appear later in the season and include wilting, premature ripening, failure of pods to fill, and dead, infected crop areas. Grey mouldy growth on stems and pods is visible throughout the canopy (Fig. 3). These are the sources of the clouds of spores seen dispersed during harvesting. Sclerotinia: Root system and base of plant brown and rotten and may have white mould
growing on them (Fig. 3). Plants first turn yellow, later infected areas become bleached and shredded. When and how often should I scout my lentil crop for ascochyta and anthracnose? Early identification of diseases is critical as it allows for timely decisions to commence fungicide application and minimize crop damage. Begin scouting at the 8 - 10 node stage (prior to flowering) and scout every 5 - 7 days.
How do I scout for ascochyta and anthracnose in my lentil crop? Start with high risk areas and fields. Select and flag 5 to 10 random locations (in an “M” pattern) in the field. Early symptoms are similar for both diseases. At each point, look for small (pinhead size) brown to dark brown spots at the lower parts of the plants. Use a magnifying glass and field guides with photos. Under humid conditions, these spots expand quickly into lesions described under symptoms above. Note that anthracnose lesions are more commonly observed on stems. Who can help me diagnose these diseases? It is advised that you use field guides with photos or seek assistance of a qualified agronomist. For conclusive identification, send a sample to the Provincial Crop Protection Lab (306-787-8130). How do I prepare samples for submission to Crop Protection Lab? To ensure that samples get to the lab in the best condition, keep them moist and aerated. Dig the plants out with a lump of soil still attached to the roots. Moisten the soil and wrap a plastic film around the soil and base of the plant. Place the whole plant in a box that allows air circulation. Mail the samples to the lab, preferably by courier. Avoid sending samples at the end of the week as they may get stuck in the mailroom over the weekend. For
sample submission forms see the SAF website at: How do I control these diseases in my lentil crop? A number of foliar fungicides are registered for the control of both ascochyta and anthracnose – namely: Bravo, Dithane, Headline and Quadris. Lance is registered for the control of ascochyta blight, sclerotinia and botrytis. See the SAF Guide to Crop Protection in Saskatchewan for details on foliar fungicides. How early and how often should I spray fungicides? The optimal time for control of ascochyta and anthracnose is at the 10 - 12 node stage or early flowering. It is too late to control anthracnose when severe lesions can be found at the stem base, and when the crop is no longer flowering. The threshold for fungicide application is set at a risk value of 50 (Table 1). If the risk value is less than 50, a fungicide application is not warranted, but a new risk assessment should be made at 3-5 days intervals until the crop is no longer flowering. If well timed, a single fungicide application is usually sufficient in controlling lentil diseases.
Adopted from Buchwaldt et al. 2001
How much yield reduction can the crop suffer? If ascochyta spreads to the top of the canopy and wet conditions prevail, infection may lead to flower and pod abortion resulting in significant yield losses – as much as 50%. More economic losses are incurred due to reduction in grain quality. Anthracnose is capable of causing yield losses in excess of 50% and is much more destructive than ascochyta. How can I prevent these diseases? Crop rotation is key to preventing these diseases as it allows time for the lentil residue on which the fungi survive to decompose. Allow 4 years between lentil crops. The highest levels of anthracnose are usually observed on fields with a history of lentils every second year. Avoid planting lentil adjacent to previous year’s lentil fields to reduce residue and windborne spread of the pathogens. Plant seed that has been tested at an acredited lab and known to have zero or acceptable levels of seed borne diseases and high germination. Use seed treatments to protect the seed and seedlings from seed-borne diseases. Choose varieties classified as disease resistant when available. References L. Buchwaldt, B. D. Gossen and P. Pearse
2001. Ascochyta
blight of lentil.
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