Lentil Disease Diagnostic Series (PP1913, Jan. 2019)
Availability: Web only
Pythium seed and seedling rot
Pythium ultimum, P. irregulare, P. aphanidermatum and other Pythium species
FIGURE 1 – Brown/black discoloration and pruning of lateral and tap roots by Pythium irregulare
Photos: T. Paulitz, USDA-ARS, Pullman, Wash.
FIGURE 2 – Range of yellowing on plant foliage
Photo: T. Paulitz, USDA-ARS, Pullman, Wash.
SYMPTOMS
• Poor emergence, rotted seed with light brown root discoloration
• Stunted plants with yellow or purple leaves developing from the bottom
• 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
FIGURE 1 – Brown to reddish-brown lesions on lower stems and roots caused by Fusarium infection
Photo: K. Zitnick-Anderson, NDSU
FIGURE 2 – Infected seedlings
Photo: K. Zitnick-Anderson, NDSU
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
FIGURE 1 – Sunken brown lesions on stem and root just below soil
Photo: K. Zitnick-Anderson, NDSU
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
FIGURE 1 – Infected roots with caramel-brown root rot (R), compared with healthy roots (L)
Photo: L. Porter, USDA-ARS, Prosser, Wash.
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
FIGURE 1 – Small black fungal resting structures (microsclerotia) within anthracnose lesions
Photo: Michael Wunsch, NDSU
FIGURE 2 – Severe anthracnose lesions coalescing
Photo: Michael Wunsch, NDSU
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
Photo: Michael Wunsch, NDSU
FIGURE 2 – Mid-canopy Ascochyta blight lesions
Photo: Michael Wunsch, NDSU
FIGURE 3 – Discolored seeds produced in pods with Ascochtya lesions
Photos: Michael Wunsch, NDSU
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
FIGURE 1 – Gray sporulation on diseased tissues when relative humidity is high
Photo: Michael Wunsch, NDSU
FIGURE 2 – Dead patches in lentil field
Photos: Michael Wunsch, NDSU
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
FIGURE 1 – Tan to light brown lesions at disease onset
Photos: Michael Wunsch, NDSU
FIGURE 2 – Diseased leaflets that have become dark brown to gray due to pathogen sporulation under high relative humidity
Photos: Michael Wunsch, NDSU
FIGURE 3 – Defoliated plants that have shed diseased leaves
Photos: Michael Wunsch, NDSU
SYMPTOMS
• Leaflets may exhibit angular lesions at disease onset
• Disease is most severe on leaves but also infects pods, stems and petioles
• 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
FIGURE 1 – Brown, circular and translucent foliar lesions
Photo: F. Mathew, South Dakota State University
FIGURE 2 – Bacterial ooze from pod lesions
Photo: R. Harveson, University of Nebraska
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
FIGURE 1 – Early infection - white “powdery” spots
Photo: L. Porter, USDA-ARS, Prosser, Wash.
FIGURE 2 – Leaf and stem surfaces covered with powdery mildew
Photo: L. Porter, USDA-ARS, Prosser, Wash.
W. Chen, USDA-ARS, Pullman, Wash.
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
Photo: W. Chen, USDA-ARS, Pullman, Wash.
FIGURE 2 – White, fluffy fungal growth on leaves and stems
Photo: L. Dighans, Pro Co-op Ag Center, Scobey, Mont.
Photo: W. Chen, USDA-ARS, Pullman, Wash.
Photo: W. Chen, USDA-ARS, Pullman, Wash.
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)
FIGURE 1 – Twisted and malformed leaves
Photo: W. Chen, USDA-ARS, Pullman, Wash.
FIGURE 2 – Leaf mottling
Photo: W. Chen, USDA-ARS, Pullman, Wash.
FIGURE 3 – Leaf mottling
Photo: W. Chen, USDA-ARS, Pullman, Wash.
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)
FIGURE 1 – Early leaf yellowing symptoms
Photo: B. Agindotan, Montana State University, Bozeman
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