Rhizoctonia solani is a common soil inhabitant which can survive many years in the absence of a soybean crop. In addition to being a parasite of soybeans, Rhizoctonia solani can survive on crop debris and in soil as black to brownish resting structures (sclerotia) or as resting fungal mycelium (threadlike material). Damage to soybeans is dependent on many factors including soil moisture and temperatures, soil pH, herbicides used, fertility levels, and competition from other soil microorganisms. Generally, any factor that slows or delays seedling growth and development will affect the level of losses to Rhizoctonia.
Certain herbicides have been shown to have both direct and indirect effects on this fungus. Some herbicides may inhibit soil microorganisms which normally compete with Rhizoctonia, allowing a rapid buildup of the fungus. Others may cause growth stresses on young plants, making them more susceptible to injury by Rhizoctonia. Excessive herbicide rates, improper application, or poor incorporation may also affect the level of Rhizoctonia.
Fertility may also have an important role in disease losses. Damage is usually greatest where phosphorous or potash are deficient or where pH levels are unfavorable. Rhizoctonia can also invade tissues at wound sites. Stem infections, hail injury, or mechanical damage from equipment are common and can result in plant death especially when warm, wet conditions prevail.
1. Plant only clean, certified seed with a known cold germination of at least 70 percent or a warm germination of at least 85 percent. High vigor seed is especially important where conditions do not favor rapid germination and emergence.
2. Plant in a warm (above 60 F), well-prepared seedbed. If planting in reduced tillage fields with a history of Rhizoctonia problems, delay planting due to the slower warm-up of soils under residue covers.
3. Treat seed with a protectant fungicide which will control Rhizoctonia.
4. Avoid chipped, cracked, or discolored seed.
5. Test soils before planting and maintain proper balanced fertility and pH
based on a soil test.
8. Apply only suggested herbicides at recommended rates and properly incorporate according to label. Follow current recommendations of University of Illinois Extension Agronomists.
9. Where Rhizoctonia has been diagnosed on seedlings, cultivate to move soil around the base of plants to encourage the development of adventitious roots. This can save a stand. However, note the situation and plan appropriate action to prevent recurrence in the future.Back to Top
For further information concerning diseases of crucifers and other vegetables, contact Mohammad Babadoost, Extension Specialist in Fruit and Vegetable Diseases, Department of Crop Sciences, University of Illinois at Urbana-Champaign.
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