Seed Rot, Root Rot, Seedling Blight; Rhizoctonia Root Rot, Fusarium Root Rot, Aphanomyces Root Rot 

CAUSED BY

• Pathogens (various fungal and fungus-like organisms) associated with Root Rot often appears as a complex, where more than one pathogen is present, making identification of the primary causal agent difficult. 
• These pathogens are caused by several fungi including Pythium, Rhizoctonia solani, Botrytis, and Fusarium species.
• They are seed or soil-borne and can infect the plant at any stage between germination and maturity, and any part of the root system up to a short distance above the soil surface.
• They are common in the soil, and infection is more likely if the soil around the seed is excessively wet. Warm and moist conditions generally favour these diseases, but cold and wet is also detrimental because the cool temperatures slow plant development and add additional stress.
• Soil compaction and poor seed quality can also play a role.
• Other factors, including abiotic conditions such as flooding and soil oxygen depletion can result in root cell death. 

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 mould 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.
• Typically occur in patches and may expand if conditions are favourable for the pathogens over several growing seasons.  Symptoms are often associated with areas of flooding or waterlogging.

PREVENTION AND CONTROL

• As prevention measure, seed treatments offer protection to the developing seedling, especially under cool, wet conditions when emergence may be delayed.
• A four to five-year rotation out of lentils or other susceptible hosts.
• Use seed with high vigour, practice good soil fertility, liming of acid soils and ripping to reduce soil compaction.
• Once Root Rot has set in, there is nothing that can be done.  Understanding the disease, identifying the risks for Root Rot infection, and thorough planning for prevention are the only current options.
• 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.

IMPACT

• Yield loss, stunting of plants.

RESOURCES

• 2017 Root Rot in Peas and Lentils in Western Canada
• Aphanomyces Root Rot in Peas and Lentils in Western Canada pdf (941 KB)
• Testing for Aphanomyces Root Rot pdf (493 KB)

Botrytis (Grey Mould)

CAUSED BY

• Caused by Botrytis cinerea Pers. ex Fr.
• Botrytis Stem and Pod Rot is also known as Grey Mould.
• Can be seed-borne, soil-borne, stubble-borne, air-borne, and can attack at various stages of plant growth.
• Grey Mould 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

• Grey Mould first appears on lentil flowers as a dirty, white mouldy growth. On older plants, it appears as a greyish, mouldy growth on flowers, pods, or lower areas of the stem.
• The infected sites first develop small water-soaked grey lesions on lower areas of the stem and spread until the entire lower foliage turns a fuzzy, grey colour.
• Pod infection causes the most damage, and clinging blossoms provide a humid environment from which the tip of the young pod can be infected – small, oval, water-soaked lesions develop and spread up the pod (these lesions are tan at first but turn greyish with age and often develop sclerotia in the form of small black specks).
• As the disease progresses, watch for wilting, leaves become shriveled and dry, premature ripening, failure of pods to fill and dead infected crop areas.

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. Potassium fertilizer in potassium deficient soils reduces the severity of Grey Mould.