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Lentil Disease Diagnostic Series

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(PP1913, Jan. 2019)

A continuation of the Disease diagnostic series cards, these are funded externally and will be distributed to growers and other stakeholders.

Julie Pasche, Dry Bean and Pulse Crop Pathologist, North Dakota State University

Audrey Kalil, Plant Pathologist, Williston Research Extension Center, North Dakota State University; Samuel Markell, Extension Plant Pathologist, North Dakota State University

Availability: Web only


Contents
  1. Pythium seed and seedling rot
  2. Fusarium root rot
  3. Rhizoctonia seed, seedling and root rot
  4. Aphanomyces root rot
  5. Anthracnose
  6. Ascochyta blight
  7. Botrytis gray mold
  8. Stemphylium blight
  9. Bacterial blight
  10. Powdery mildew
  11. White mold (Sclerotinia stem rot)
  12. Pea enation mosaic
  13. Bean leaf roll

Pythium seed and seedling rot

Pythium ultimum, P. irregulare, P. aphanidermatum and other Pythium species

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FIGURE 1 – Brown/black discoloration and pruning of lateral and tap roots by Pythium irregulare
Photos: T. Paulitz, USDA-ARS, Pullman, Wash. 

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 FIGURE 2 – Range of yellowing on plant foliage
Photo: T. Paulitz, USDA-ARS, Pullman, Wash.

AUTHORS:Lyndon Porter, Timothy Paulitz and Kurt Schroeder

SYMPTOMS

• Poor emergence, rotted seed with light brown root discoloration
• Stunted plants with yellow or purple leaves developing from the bottom

FACTORS FAVORING DEVELOPMENT

• Cool, water-saturated or compacted soil and poor seed vigor

IMPORTANT FACTS

• Metalaxyl (mefenoxam)-resistant Pythium is present in some growing regions
• Effective seed treatments are available for metalaxyl-resistant and sensitive Pythium
• Avoid planting into wet or compacted soils
• Pathogen survives on plant debris and in soil
• Resistant varieties are not available
• Often occurs in complex with other root rots
• Can be confused with other root rots and water logging


Fusarium root rot

Fusarium avenaceum and other Fusarium species

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FIGURE 1 – Brown to reddish-brown lesions on lower stems and roots caused by Fusarium infection
Photo: K. Zitnick-Anderson, NDSU

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FIGURE 2 – Infected seedlings
Photo: K. Zitnick-Anderson, NDSU

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FIGURE 3 – Yellowing progressing upward and premature death caused by F. avenaceum (diseased [middle/bottom] and healthy [top] roots)
Photo: L. Porter, USDA-ARS, Prosser, Wash.

AUTHORS: Audrey Kalil and Lyndon Porter

SYMPTOMS

• Poor emergence
• Wilting, stunting and premature death

FACTORS FAVORING DEVELOPMENT

• Soil compaction and plant stress
• Warm, moist soil (68 to 82 F)
• Short pea and lentil rotations

IMPORTANT FACTS

• Pathogen survives on plant debris and in soil
• Often occurs in complex with other root diseases
• Resistant varieties are not available
• Fungicide seed treatments may be recommended
• Can be confused with other root rots and water logging


Rhizoctonia seed, seedling and root rot

Rhizoctonia solani

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FIGURE 1 – Sunken brown lesions on stem and root just below soil
Photo: K. Zitnick-Anderson, NDSU

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FIGURE 2 – Moderate (top) to severe (bottom) Rhizoctonia root rot
Photo: K. Zitnick-Anderson, NDSU

AUTHORS: Jessica Rupp, Myron Bruce and Timothy Paulitz

SYMPTOMS

• Poor emergence
• Reddish-brown to dark brown lesions on roots and base of stem
• Secondary roots absent
• Plants are stunted and leaves turn yellow

FACTORS FAVORING DEVELOPMENT

• Wet, compacted or waterlogged soils

 IMPORTANT FACTS

• Pathogen survives on plant debris and in soil
• Resistant varieties are not available
• Fungicide seed treatments may be recommended
• Often occurs in a complex with other root rots
• Can be confused with other root rots and water logging


Aphanomyces root rot

Aphanomyces euteiches

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FIGURE 1 – Infected roots with caramel-brown root rot (R), compared with healthy roots (L)
Photo: L. Porter, USDA-ARS, Prosser, Wash.

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FIGURE 2 – Infection moving up primary stem
Photo: L. Porter, USDA-ARS, Prosser, Wash.

AUTHORS: Lyndon Porter

SYMPTOMS

• Root rot may extend slightly above the soil line
• Leaf yellowing progresses from lower canopy upward
• Early season stunting and premature plant death

FACTORS FAVORING DEVELOPMENT

• Cool, wet spring conditions
• High soil moisture
• Short rotations with peas and lentils

 IMPORTANT FACTS

• Chickpea, cereals and faba bean are not important hosts
• Often occurs in a complex with other root rot diseases
• Can survive for many (20) years in soil without a susceptible host
• Seed treatments and genetic resistance are not effective
• Can be confused with other root rots and water logging


Anthracnose

Colletotrichum species

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FIGURE 1 – Small black fungal resting structures (microsclerotia) within anthracnose lesions
Photo: Michael Wunsch, NDSU

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FIGURE 2 – Severe anthracnose lesions coalescing
Photo: Michael Wunsch, NDSU

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FIGURE 3 – Anthracnose-infected pods and discolored seeds
Photo: Michael Wunsch, NDSU

AUTHORS: Michael Wunsch and Julie Pasche

SYMPTOMS

• Light-brown stem lesions with a dark border
• Symptoms initiate at the base of plant and spread upward
• Patches of dead plants develop when stem lesions girdle plant

FACTORS FAVORING DEVELOPMENT

• Abundant rainfall during bloom and pod development
• Wide range of temperatures; 68 to 74 F optimal
• Dense canopy

IMPORTANT FACTS

• Seed quality declines with increasing anthracnose severity
• Varieties differ in susceptibility to anthracnose; none are resistant
• No-till increases degradation of pathogen resting structures
• Commonly confused with Ascochyta blight


Ascochyta blight

Ascochyta lentis

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FIGURE 1 – Concentric ring pattern from pycnidia inside the light brown lesion
Photo: Michael Wunsch, NDSU

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 FIGURE 2 – Mid-canopy Ascochyta blight lesions
 Photo: Michael Wunsch, NDSU

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FIGURE 3 – Discolored seeds produced in pods with Ascochtya lesions
Photos: Michael Wunsch, NDSU

AUTHORS:Michael Wunsch and Julie Pasche

SYMPTOMS

• Light brown leaf, stem and pod lesions with dark brown borders
• Small brown fungal fruiting structures (pycnidia) within lesions
• Disease lesions and/or picnidia within lesions often exhibit a concentric ring pattern (unlike anthracnose)
• Flower and pod abortion

FACTORS FAVORING DEVELOPMENT

• Cool, wet weather; 50 to 68 F optimal
• Planting lentils immediately adjacent to a field where Ascochyta blight occurred on lentils the previous year

IMPORTANT FACTS

• Ascochyta blight is seed-borne and seed-transmitted; seed should be tested
• Managed with crop rotation (minimum two years out of lentils) and foliar fungicides
• Commonly confused with anthracnose


Botrytis gray mold

Botrytis cinerea, B. fabae

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FIGURE 1 – Gray sporulation on diseased tissues when relative humidity is high
Photo: Michael Wunsch, NDSU

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FIGURE 2 – Dead patches in lentil field
Photos: Michael Wunsch, NDSU

AUTHORS:Michael Wunsch and Julie Pasche

SYMPTOMS

• Gray fungal growth on diseased stems, leaves and pods in the lower canopy
• Plant tissue is light brown to bleached
• Plants become chlorotic, wilt and die when lesions girdle the lower stem
• Plant-to-plant spread of Botrytis is common, resulting in dead patches

FACTORS FAVORING DEVELOPMENT

• Dense crop canopies that restrict airflow
• High relative humidity and frequent rainfall
• Cool temperatures; 59 to 77 F optimal

IMPORTANT FACTS

• Resistant varieties are not available
• Fungicides can be effective if applied preventatively
• Commonly confused with white mold and anthracnose


Stemphylium blight

Stemphylium botryosum

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FIGURE 1 – Tan to light brown lesions at disease onset
Photos: Michael Wunsch, NDSU 

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FIGURE 2 – Diseased leaflets that have become dark brown to gray due to pathogen sporulation under high relative humidity
Photos: Michael Wunsch, NDSU

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FIGURE 3 – Defoliated plants that have shed diseased leaves
Photos: Michael Wunsch, NDSU

AUTHORS:Weidong Chen and Michael Wunsch

SYMPTOMS

• Leaflets may exhibit angular lesions at disease onset
• Disease is most severe on leaves but also infects pods, stems and petioles

FACTORS FAVORING DEVELOPMENT

• Extended periods of high relative humidity in the last third of the growing season
• Warm temperatures; 77 to 86 F optimal

IMPORTANT FACTS

• Red lentils are generally more susceptible than green lentils
• Managed with fungicides and partially resistant varieties
• Can be confused with nutrient deficiencies (such as low nitrogen) or plant senescence


Bacterial blight

Pseudomonas syringae pv. syringae

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FIGURE 1 – Brown, circular and translucent foliar lesions
Photo: F. Mathew, South Dakota State University

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FIGURE 2 – Bacterial ooze from pod lesions
Photo: R. Harveson, University of Nebraska

AUTHORS:Febina Mathew, Bob Harveson and Bright Agindotan

SYMPTOMS

• Lesions observed on all above-ground plant parts
• Initial lesions are water-soaked and become necrotic through time
• Bacteria may ooze from lesions under high-humidity conditions

FACTORS FAVORING DEVELOPMENT

• Warm temperatures
• High humidity or moisture on leaves
• Hail

IMPORTANT FACTS

• Bacteria can be spread by rain, wind and mechanical means
• P. syringae pv. syringae can cause disease on soybean, dry edible beans and other legumes
• Physical damage (such as hail) can facilitate infection and spread
• Fungicides are not effective
• Planting infected seed can increase disease risk
• Can be confused with Ascochyta blight or anthracnose


Powdery mildew

Erysiphe pisi and Leveillula taurica

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FIGURE 1 – Early infection - white “powdery” spots
Photo: L. Porter, USDA-ARS, Prosser, Wash.

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FIGURE 2 – Leaf and stem surfaces covered with powdery mildew
Photo: L. Porter, USDA-ARS, Prosser, Wash.

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FIGURE 3 – Feltlike white fungal growth
W. Chen, USDA-ARS, Pullman, Wash.

AUTHORS:Lyndon Porter and Weidong Chen

SYMPTOMS

• Most visible starting at flowering and later in the season
• Infected leaves can become chlorotic/necrotic and curled
• Infection begins as small spots that enlarge quickly and cover plant surfaces

FACTORS FAVORING DEVELOPMENT

• Late planting
• Conditions limiting sunlight
• Temperatures of 59 to 77 F are optimal

IMPORTANT FACTS

• Pathogen can be soil-borne, seed-borne and wind-dispersed
• Fungicides may be effective if applied early in disease development
• Crop rotation is important
• Lentil varieties have differing levels of resistance
• Can be confused with white mold and the fungal growth of saprophytes or other pathogens


White mold (Sclerotinia stem rot)

Sclerotinia sclerotiorum

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FIGURE 1 – Dead patches of plants
Photo: W. Chen, USDA-ARS, Pullman, Wash.

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FIGURE 2 – White, fluffy fungal growth on leaves and stems
Photo: L. Dighans, Pro Co-op Ag Center, Scobey, Mont.

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FIGURE 3 – Bleached lesions with white fungal growth
Photo: W. Chen, USDA-ARS, Pullman, Wash.

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FIGURE 4 – Dark, hard fungal structures (sclerotia) on the soil surface
Photo: W. Chen, USDA-ARS, Pullman, Wash.

 

AUTHORS:Mary Burrows, Weidong Chen and Michael Wunsch

SYMPTOMS

• First observed as water-soaked lesions
• Lesions enlarge and become bleached
• White fluffy fungal growth may appear under high humidity
• Hard, black sclerotia may appear late in the season
• Wilting

FACTORS FAVORING DEVELOPMENT

• Cool, wet conditions after canopy closure
• Short rotations with susceptible crops
• Lush canopy

IMPORTANT FACTS

• Sclerotia survive in the soil for several years
• Pathogen infects most broadleaf plants
• Fungicides can be effective if applied preventatively
• Can be confused with powdery mildew, nutrient deficiencies (low nitrogen) or plant senescence


Pea enation mosaic

Pea enation mosaic virus (PEMV)

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FIGURE 1 – Twisted and malformed leaves
Photo: W. Chen, USDA-ARS, Pullman, Wash.

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FIGURE 2 – Leaf mottling
Photo: W. Chen, USDA-ARS, Pullman, Wash.

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FIGURE 3 – Leaf mottling
Photo: W. Chen, USDA-ARS, Pullman, Wash.

AUTHORS:Lyndon Porter, Bright Agindotan and Kevin McPhee

SYMPTOMS

• Small, circular to elongated translucent spots or streaks on leaves
• Vein clearing
• Stunted growth and malformed pods

FACTORS FAVORING DEVELOPMENT

• Presence of aphid vectors, including pea, cowpea, green peach, potato or foxglove
• Movement of aphids from virus-infected overwintering hosts in the spring or alfalfa fields during cuttings

IMPORTANT FACTS

• Can infect chickpea, pea, faba bean, vetch, crimson clover and lambsquarters
• PEMV is not seed-transmitted
• No known resistant varieties
• Insecticides applied to manage aphid vector may help reduce secondary spread
• Can be confused with other viruses or damage from herbicides or thrips


Bean leaf roll

Bean leaf roll virus (BLRV)

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FIGURE 1 – Early leaf yellowing symptoms
Photo: B. Agindotan, Montana State University, Bozeman

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FIGURE 2 – Advanced stage of yellowing (Infected [L, R] and healthy [C])
Photo: B. Agindotan, Montana State University, Bozeman

AUTHORS: Bright Agindotan and Lyndon Porter

SYMPTOMS

• Yellowing and stunting
• Small leaves

FACTORS FAVORING DEVELOPMENT

• Presence of other BLRV-infected legume crops and weeds
• Presence of aphid vectors, including pea, cowpea, potato and vetch
• Movement of aphids from alfalfa fields during cuttings

IMPORTANT FACTS

• Leaf rolling absent
• BLRV is not seed-transmitted
• BLRV infects pea, chickpea, lentil, alfalfa and other legumes
• Insecticides applied to manage aphid vectors may help reduce secondary spread
• Resistant varieties may be available
• Can be confused with nutrient deficiencies (low nitrogen) or plant senescence

January 2019

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