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Lentil Diseases

Ascochyta Blight

  • caused by Ascochyta fabae f. sp. lentis
  • can spread rapidly on stubble or seed in a field with cool, wet conditions
  • spores are spread through rain splash – they can survive up to five years on the soil surface and up to 30 years in the seed

Symptoms

  • symptoms appear on leaflets, pods and stems as tan spots surrounded by a dark margin
  • tiny black specks known as pycnidia occur in the center of the spot
  • branch tips wilt, turn brown and often die – premature drop occurs from infected leaflets
  • can also cause flower and pod abortions – infected seeds turn purplish-brown and are often shrivelled and smaller in size (severely infected seed can also have whitish patches of mycelia, strands of threadlike material, with tiny black pycnidia on the surface)

Causes

  • Cool temperatures
  • High humidity in the canopy
  • Rain-splashed spores
  • Air-borne spores

Prevention and Control

  • bury all crop residues
  • avoid seeding next to the previous year’s pulse fields
  • allow at least 4 to 5 years between lentil crops
  • use disease-free treated seed
  • can be treated with Crown® (carbathiin and thiabendazole) fungicide
  • Bravo 500® (chlorothalonil), a post-emergent fungicide, can be applied at early flowering and can be repeated up to three times if conditions favour disease development

Anthracnose

  • caused by Colletotrichum truncatum
  • can be borne by seed or stubble
  • since spores are spread by splashing rain, anthracnose thrives under warm, moist weather, frequent showers and dense canopies
  • spores can survive on stubble for up to two years

Symptoms

  • appears as grey to cream-coloured spots on leaves and tan to brown lesions on stems
  • the entire lower stem may become covered in lesions, giving it a brown, rough appearance
  • pod lesions are circular and sunken with reddish-brown margins and reddish centres; close examination of pod lesions often reveals fruiting bodies with orange-pink spores
  • leaf and stipule lesions are oval, with brown margins and greyish centres, and stem lesions are elongated, appearing as a coppery colour when moist and greyish when dry
  • this stage is generally followed by die back of leaves and extensive loss of leaves – entire plants may die back and stems take on a blackish colour
  • brownish seed discolouration can also occur

Causes

  • Warm temperatures
  • High humidity
  • Recurrent rains (spores are spread by splashing rain)
  • Dense canopies

Prevention and Control

  • apply various registered fungicides prior to flowering, and repeat if conditions for disease development are favourable
  • seed treatments can be used for seed-borne infections of this disease
  • allow 4 to 5 years between lentil and other susceptible crops such as pea and faba bean
  • use disease-free seed
  • apply the fungicide Bravo 500® at early flowering, and repeat if conditions for disease development are favourable
  • Crown® can also be used as a seed treatment for seed-borne pathogens of this disease

Botrytis Stem & Pod Rot

  • caused by Botrytis cinerea Pers. ex Fr.
  • botrytis stem and pod rot is also known as grey mold
  • can be seed or soil-borne and favours cool, moist conditions and a thick plant canopy, such as found under irrigation
  • more common on early-seeded crops
  • infected seed produces infected seedlings, which die soon after emergence

Symptoms botrytis

  • stem and pod rot first appears on lentil flowers as a dirty, white moldy growth
  • watch for wilting, premature ripening, failure of pods to fill and dead infected crop areas
  • a greyish, moldy growth occurs on the surface of the pods and stems

Prevention and Control

  • since no fungicides are registered for control at this time, the only practical prevention measure is to avoid growing lentil under irrigation

Sclerotinia Stem & Pod Rot

  • caused by Sclerotinia sclerotiorum (Lib.) de Bary
  • sclerotinia stem and pod rot flourishes under dense canopies and high humidity

Symptoms

  • the first sign of sclerotinia infection will be seen as cottony threadlike (mycelia) growth in the collar region
  • dark brown spots then develop on the stem and the entire plant eventually turns brown
  • affected plants often appear wilted and ripen prematurely due to rotting of the stems – lodging is common in affected areas
  • hard, black, irregularly shaped structures (sclerotia) form in the mycelia, and these are harvested with seed or drop to the soil to reinfect in subsequent years

Prevention and Control

  • no fungicides are registered in Canada for use on lentils at this time
  • to reduce the incidence of sclerotinia, use both a four to five-year rotation out of susceptible crops such as canola, bean, faba bean, sunflower and mustard and deep burial of sclerotia

Seedling Blight & Root Rot

  • caused by a complex of pathogens including Fusarium spp., Pythium spp., and Rhizoctonia solani.
  • normally affects only scattered plants and does not spread far

Symptoms

  • first appear as water-soaked lesions on the roots that eventually turn reddish brown
  • decay often begins on the feeder roots and progresses gradually towards the main root (in some cases, all roots are destroyed)
  • symptoms on foliage are also progressive, ranging from a few yellow leaves to pronounced yellowing of the top growth, plant wilting and severe stunting
  • the root system and base of the stem turn brown and rotten and may have white or pink mold growing on them
  • these foliar symptoms often appear following warm temperature and heavy rainfall
  • infected seedlings usually die, resulting in poor stands, and infected plants lack vigour and often yield poorly

Causes

  • Warm temperatures
  • Wet soils
  • Soil compaction
  • Poor seed quality

Prevention and Control

  • using high quality seed and treating the seed is the best way to manage this disease
  • fungicide use has no effect as the products are not carried to the roots, and by the time symptoms are noticed, it is too late
  • no fungicides are registered for control at this time, but a four to five-year crop rotation will keep inoculum levels of these fungi low

Grey Mold

Description

Caused by Botrytis cinerea Pers. ex Fr., Grey Mold in lentil can be seed-, stubble- , air- and soil-borne and can attack at various stages of plant growth. Infected seed produces infected seedlings, which die before emergence or soon after. On older plants, a greyish mold is observed, which quickly spreads under moist conditions.

Causes

  • Cool temperatures
  • High humidity
  • Wet soils
  • Dense canopies

Symptoms

On young plants that emerge, the Grey Mold appears as a grey moldy growth visible at the soil surface. On older plants, it appears as a fuzzy grey or dirty white moldy growth on flowers, pods, or lower areas of the stem. The infected sites first develop small water-soaked lesions that expand to form large brown lesions with concentric zones. Under humid conditions, massive greyish-brown spores are produced to cover the infected tissues. Sometimes, black sclerotia may be formed on old infected tissues. These lesions spread to the entire lower foliage. As the disease progresses, wilting, premature ripening, failure of pods to fill, and dead infected crop areas occur.

Treatment & Prevention

  • Treat seed or plant disease free seed.
  • Use wider row spacing or lower seeding rates to improve air circulation in the crop.
  • No fungicides are registered for control in many of the pulse crops, and control products in bean are not considered economical.
  • Potassium fertilizer in potassium deficient soils reduces the severity of Grey Mold in lentil.

White Mold

Description

Often called White Mold or pod rot, Sclerotinia rot is caused by Sclerotinia sclerotiorum. The critical infection period is during the flowering stage. While White Mold is of minor importance in most pulse crops, it can cause severe losses in bean, where the infection can spread quickly. Sclerotinia overwinters in infected crop debris and soil.

Causes

  • Cool temperatures
  • High humidity
  • Dense canopies
  • Growing pea and canola in the same rotation

Symptoms

The first sign of White Mold is the appearance of a light brown, water-soaked discolouration on the stem, leaves, or pods and a cottony threadlike growth in the collar region if the temperature and humidity levels remain high. A water-soaked area appears that spreads both upwards and downwards. Dark brown spots then develop on the stem, and the entire plant eventually turns brown. Affected plants often appear wilted and ripen prematurely due to rotting stems; lodging is common in affected areas. Stems, when split open, exhibit characteristic white fungus growth — numerous, black, hard resting bodies (sclerotia) may be present in the pith. Affected plants yield poorly and often die prematurely.

Treatment & Prevention

  • Bury all crop residues.
  • Fungicide use for control of Sclerotinia stem rot in the majority of pulse crops is not cost-effective because, once the canopy closes, the fungicides cannot reach their target.

Viruses

  • several viruses attack lentil, including pea seed-borne mosaic virus (PsbMV), alfalfa mosaic, bean yellow mosaic, cucumber mosaic and pea leaf roll virus
  • only PsbMV is considered a slight threat in Alberta
  • viruses are not considered a serious threat because of Alberta’s severe winters and short growing season

Heat Canker

  • not caused by a pathogen, but occurs from contact of young tender shoots with soil hot from exposure to the sun
  • occurs on seedlings in late May and early June when very hot weather occurs

Symptoms

  • the base of the stem is pinched at the soil surface, the leaves turn yellow and the plant usually wilts, falls over and dies
  • below the soil surface, the stem and roots remain plump, white and healthy

Control

  • seeding in a north-south direction and shading provided by stubble offers some protection against heat canker