Cause Fusarium oxysporum f. sp. raphani (= F. oxysporum f. sp. conglutinans) or a Verticillium longisporum (a variant of V. dahliae, formerly known as V. dahliae var. longisporum) have both been found in red radish seed fields within the Pacific Northwest. Both fungi survive in soil as durable resting structures; chlamydospores produced by Fusarium and microsclerotia of V. longisporum can survive years between hosts. These fungi can be spread through soil movement on equipment, tools, and footwear as well as infested soil being windborne or waterborne. Fusarium can also produces spores that can be moved with wind or water. Both of these fungi can be seedborne.
Symptoms Early symptoms include yellowing of lower leaves, sometimes one-sided or V-shaped in appearance. Wilting of plants is observed more commonly once flowering commences and yellowing spreads to younger leaves. Often the entire plant dies and remaining stems are silvery-tan in color. Dark-brown to blackish discoloration can found around vascular elements in storage roots (radish bulb) and sometimes is evident aboveground in stems. Vascular discoloration precedes wilting symptoms.
Cultural control
- Plant pathogen-free seed in pathogen-free soil.
- Avoid establishment of seed fields in soils with high levels of plant residues or organic amendments.
- Remove and destroy infected plants.
- Long rotations are required to rid infested ground of this Fusarium; rotate out of susceptible red radish for 18 to 20 years.
Biological control
- Double Nickel LC at 0.5 to 4.5 pints/A for soil application on 14- to 28-day intervals. Can be applied the day of harvest. 4-hr reentry. O
- Prestop at 1.4 to 14 oz/10 gal water (0.1 to 1.0% suspension) as a soil drench or incorporation into growing medium. 0-hr reentry. O
- Regalia at 1 to 24 quarts/A as an in-furrow treatment. 4-hr reentry. O
- Stargus at 6 to 8 fl oz per 1,000 ft row as an in-furrow treatment, 3 to 4 quarts/A as a soil drench on 10- to 14-day intervals, or 3 to 4 quarts/A as a chemigation drip treatment on 14- to 21-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
- Tenet WP at 2.5 to 5.0 lb/A at sowing will suppress certain fungal pathogens including Fusarium, Rhizoctonia, and Pythium spp. See label for specific application types and timings. 1-hr reentry. O