CAUSED BY

• Root Rot and Seedling Blight are common diseases of dry bean.
• Pathogens (various fungal and fungus-like organisms) associated with root rot often appear as a complex, where more than one pathogen is present, making identification of the primary causal agent difficult. 
• These diseases are caused by several fungi including Pythium, Rhizoctonia, and Fusarium species.
• Fusarium is the most common and most problematic in drier years.
• Dry beans have a variable response to Aphanomyces. They are not resistant, and can be a host, but will only produce a few oospores and have variable symptoms from the disease
• These soil-borne fungi 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.
• These fungi 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.
• Other factors, including abiotic conditions such as flooding and soil oxygen depletion can result in root cell death. 

SYMPTOMS

• Failure of the plants to emerge from the soil indicates seed decay or seedling damping off.
• Symptoms include dark brown lesions on the tap root that can spread to all roots.
• Above-ground symptoms may not occur unless the degree of root rot is moderate to severe – then, there is likely to be stunting of the plants, yellowing of the foliage (Seeding Blight), wilting, with red to dark brown rotted areas appearing on the taproot at or below the soil line, as well as some premature defoliation and a failure to produce normal, full pods
• On larger plants, the disease often appears as a rusty brown discolouration of the tap root (root rot phase).
• Young plants may wilt and die after emergence or remain stunted and yellow (seedling blight).
• Rhizoctonia presents with chocolate to red coloured spots that are more distinct, and may have small black or brown sclerotia develop inside the stem.
• As the disease progresses, the discoloured area spreads until the entire taproot and lower stem are reddish brown and decayed, and secondary roots are usually decayed as well.
• 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 a prevention measure, seed treatments offer protection to the developing seedling, especially under cool, wet conditions when emergence may be delayed.
• Longer rotations can help reduce disease pressure, however many of the pathogens will affect other crops as well (such as Rhizoctonia, Fusarium, and Pythium), so crop rotation will have less effect.
• Fields that have grown dry bean for several years are likely to be the most severely affected by Root Rot and Seedling Blight diseases – follow a crop rotation with cereals, alfalfa, sugar beet or corn that includes bean only once every five years.
• Taking note of disease presence in previous years’ crops can help tailor seed treatment selections.
• Use seed with high vigour, practice good soil fertility, liming of acid soils and ripping to reduce soil compaction.
• Choose fields that have good tilth and no compaction problems, so plants can form hardy roots, and moisture can move freely through the soil.
• Understanding the disease, identifying the risks for root rot infection, and thorough planning for prevention are the only current options.

IMPACT

• Root Rot diseases have the second highest impact in economic importance in dry beans in Alberta.