Cause The fungus, Fusarium oxysporum f. sp. cucumerinum, which survives in soil as durable chlamydospores, or saprophytically on organic debris and in plant rhizospheres. These strains are not thought to cause wilt of watermelon or melon but may grow along the roots of other crops and weeds without causing disease. Other Fusarium species have caused wilt diseases in other countries and the species complex present in the Pacific Northwest is unclear.
Symptoms Damping-off is common in cool soil. Later infections result in wilting of a runner or even the entire plant-depending upon where the infection occurred. Plants are susceptible at any stage of development and die a few days after infection. Speed till death depends on stress such as water deficits, heat, and fruiting. Vascular discoloration in roots and stems is usually present.
- Plant resistant varieties.
- Practice long rotations.
- Use seed tested and certified pathogen-free.
- Maintain a soil pH of 6.5 to 7.0.
- Apply nitrogen as a NO3 form.
- Soil fumigation can help reduce pathogen population but will not eliminate the pathogen. Preplant fumigation with Metam sodium (Vapam HL) at various rates; see label for details. Restricted-use pesticide.
- Seed treatment may reduce disease caused by seedborne propagules.
- Treat seed with Maxim 4FS at 0.08 to 0.16 fl oz/100 lb seed. For control of pathogenic Fusarium and Rhizoctonia spp. See label for reentry restrictions.
Biological control Efficacy in the Pacific Northwest is unknown.
- Actinovate AG at 3 to 12 oz/A as soil drench at planting. 1-hr reentry. O
- Actinovate Lawn & Garden at 0.5 to 1 teaspoon/gal water. H O
- Double Nickel LC at 0.5 to 4.5 pints/A as a soil drench at planting. 4-hr reentry. O
- Prestop as a soil drench or incorporation into growing medium. 4-hr reentry. O
- Rootshield Home and Garden at 1 to 3 Tbsp/gal water as a soil drench at planting. H O
- Rootshield WP at 3 to 5 oz/100 gal water for greenhouse soil drench and field chemigation or at 16 to 32 oz/A as an in-furrow spray. 0-hr reentry. O
- Stargus at 2 to 4 quarts/A plus a nonionic surfactant on 7- to 10-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
- Taegro ECO at 2.6 to 5.2 oz/A applied as a drench, in-furrow at planting, or through drip irrigation. 24-hr reentry. O