Cause The fungus, Fusarium oxysporum f. sp. medicaginis, is a vascular fungus that can survive in soil indefinitely as durable spores (chlamydospores) or in association with plant debris. Seed can also transmit Fusarium wilt, usually by contamination of the seed coat.
Symptoms The fungus can attack a susceptible plant at any stage of growth. Infection of young plants can result in pre- or post-emergence damping-off. Infection of older plants can cause yellowing (starting in the older leaves), stunting, or wilting, and once wilting occurs, death may result. Browning of the vascular system is usually evident in the lower stem, crown, or tap root.
Cultural control
- Avoid planting on soil with a history of this disease; or practice long rotations (3 to 4 years minimum).
- Plant Fusarium-free seed.
- Liming applications to bring the soil pH to 6.5 to 7.0 can reduce disease.
Chemical control
- Seed treatment will aid with any seedborne Fusarium and suppress early stages of infections.
- Maxim 4FS at 0.08 to 0.16 fl oz/100 lb seed. See label for reentry restrictions.
- Mertect at 0.004 mg ai/seed (5.8 fl oz/100 lb seed) plus a dye.
Biological control
- Bexfond at 7 to 14 fl oz/A. O