Rhizoctonia Root and Stem Rot
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Disease Facts
- Caused by the soil-borne fungus Rhizoctonia solani
- Pathogen causes damping-off, root and stem rot, and foliage blight
- Disease is favored by heavy, poorly drained soils and delayed emergence.
- May attack soybeans from planting to mid growing season.
- Most prevalent on seedlings and young plants when prolonged wet periods are followed by warm and dry weather.
- Yield reductions can range from as little as 5% to more than 50% depending on severity.
Conditions Favoring Disease Development
- This pathogen is favored with high soil moisture and warm soil temperatures, around 81ºF (27ºC).
- Because of this, it is common in late planted soybean fields.
- Commonly occurs on heavy, poorly drained or compacted soils.
Rhizoctonia Symptoms
- Infects young seedlings, causing damping off.
- Infection is characterized by a shrunken, reddish-brown lesion on the hypocotyl at or near the soil line.
- Infection may be superficial, causing no noticeable damage, or these firm, dry, brick-red lesions can join to girdle the stem and kill or stunt plants
- Soybeans can also appear stunted, chlorotic, and wilted as a result of root decay.
- Severely affected plants may lose their leaves.
- Wilted and or dead plants often occur in small patches.
- Stems weakened by infection can cause infected plants to break at the soil line under stormy conditions.
Disease Cycle
- Disease-causing fungus survives as resting mycelium or sclerotia in the soil.
- When soils warm the fungus becomes active, and infection can occur.
- At optimum temperatures, 77-84 ° F (25-29 °C), disease severity increases.
- Infection occurs under wet conditions, but symptoms become evident under drought stress.
Soybean plants showing symptoms of damping off due to rhizoctonia root rot disease. Rhizoctonia solani can cause seed rot, root rot, and reddish-brown lesions on hypocotyls at the soil line.
Management
Seed Treatments - Offer some measure of protection and increase emergence.
Crop Rotation - Limited in its effectiveness as many strains of Rhizoctonia can infect corn, alfalfa, dry bean, and cereals.
Field Drainage and Soil Structure - Improve field drainage and remediate compaction and hardpan layers if possible.
Planting - Avoid planting under cool wet conditions.
Red discoloration at soil line due to Rhizoctonia solani.
Close up of red discoloration due to Rhizoctonia solani.