Fusarium Root Rot

By Berlin Nelson, Professor, Dept. Plant Pathology

Fusarium root rot, caused by Fusarium solani can cause damping-off of seedlings and root rot on older plants. Infected seedlings can result in poor weak stands, late emergence or stunted plants. Infected seedling roots will show reddish brown or dark to light brown discoloration and decay. The disease at this stage may be misdiagnosed as Rhizoctonia because symptoms are similar. Symptoms on older plants consist of reddish brown to black lesions on lateral roots and the tap root. In advanced stages of disease, there is decay of the cortex, the roots are black, and there are fissures in the dead surface tissues of the tap root. There may be few nitrogen fixing nodules in the roots. Plants may appear stunted or unthrifty, and there can be a yellowing (chlorosis) of the leaves (starting at the edges) with the veins remaining green for a short time. The leaves eventually become completely yellow, then die from the edges inward and fall from the petioles. These foliar symptoms are different from those caused by sudden death syndrome.

Fusarium root rot is common in North Dakota but severe damage has often been observed in association with stressed plants, such as in drought conditions or with herbicide damage. The root rot predisposes plants to damage from other stresses. High populations of the pathogen in the soil, however, may result in disease development under good growing conditions. The pathogen may interact with other pathogens such as Rhizoctonia or the soybean cyst nematode to cause disease. Disease severity may be greater in plants showing iron chlorosis.

Management.

Crop rotation will lower populations of the pathogen in the soil. When there is evidence of this disease, avoid dry beans in close rotations because the pathogen can infect dry beans. All cultivars appear to be susceptible to Fusarium root rot. Fungicide seed treatments can reduce damping-off by F. solani, but will not protect adult plant roots. Damage to seedlings often occurs during weather conditions not conducive to rapid seed germination and plant emergence. Ridging soil around the base of the plants can promote root growth and reduce damage to root rot in older plants. Use high quality seed, plant in warm well drained soils, reduce soil compaction to promote root growth and provide good soil fertility.