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Fusarium Seed and Root Rot
Causal Agent:
Fusarium seed and root rot is caused by several Fusarium spp. including Fusarium graminearum and F. oxysporum, which are the most common causal organisms for this disease of soybean in Ohio. In an earlier survey, eleven different species of Fusarium have been isolated from soybean seedings. Some isolates of F. graminearum have been shown to have reduced sensitivity to strobilurin fungicides. Additionally, F. graminearum also causes Gibberella ear and stalk rot of corn and Fusarium head scab of wheat in Ohio.
Symptoms and Signs:
Fusarium can show symptoms on several areas of the soybean plant. Root rot and seedling death are commonly associated with F. oxysporum and F. graminearum. Symptoms described here are the most commonly observed symptoms in Ohio.
Older plants are not as susceptible as younger ones. Seedling emergence will be slow and stand counts will be low. Seedlings that do emerge will be stunted and may have chlorotic, and eventually necrotic, cotyledons. Brown lesions may appear on the lower stems of the seedlings extending into the roots. Root systems will be shallow and stunted. Occasionally, there is a pink to red cast to the mycelium and the affected area.
Disease Cycle:
The fungus overwinters mainly in infected debris left in the field or in the soil as chlamydospores or fungal mycelia. If infected seed is used, this can inhibit the rate of seedling germination. The fungus will enter the plant through natural openings or wounds, but some species can penetrate the root surface directly. The fungus then grows intercellularly, colonizing all of the tissue. Disease development is favored by moist conditions. Saturated soil will greatly increase the severity of the disease; however, disease can still be present under dry conditions.
Disease Management:
Chemical applications: There are several fungicide classes available for control against Fusarium. However, resistance to several of these is shown by isolates found in Ohio. Seed treatments are available and several products have shown complete control of the pathogen. For an updated list of available and effective seed treatments for true fungi, please visit the Management section of this website.
Cultural practices: Using a standard rotation of corn-soybean-wheat will not be effective in reducing inoculum build-up of Fusarium in the field, as this pathogen uses all three crops as a host. For this reason, tillage is an important strategy to implement in order to bury any infective crop debris left in the field. Low temperatures and high amounts of moisture may also play a role in high amounts of disease incidence in the field. These conditions are common in early planting times.