By L.J. du Toit and C.M. Ocamb
Cause: Verticillium dahliae, a fungus that can survive many years in soil without a spinach crop. The fungus colonizes roots of spinach plants, from where it invades the vascular system and moves systemically up the plant into the leaves (and developing seed in spinach seed crops). The highly systemic nature of infection means the fungus readily infects developing seed in spinach seed crops planted in infested soils. The fungus is readily seed-transmitted from infected spinach seed. Isolates of V. dahliae pathogenic on spinach belong to two vegetative compatibility groups (VCG), VCG2 and VCG4.
Symptoms Symptoms of Verticillium wilt are not observed in fresh market or processing spinach crops, as symptoms only develop after bolting has been initiated (transition from vegetative to reproductive growth). Therefore, the disease only causes losses in spinach seed crops. However, planting infected spinach seed into soils can lead to infestation of the soil with the pathogen. Isolates of V. dahliae from spinach can infect potato crops. Symptoms on bolted plants start as interveinal yellowing of the lower leaves, and progress to interveinal necrosis. Symptoms then progress to younger leaves as the plant matures. Infected plants may be severely stunted with reduced seed set. Unlike Fusarium wilt, vascular tissue in roots and stems of spinach plants infected with Verticillium wilt is a light brown color.
Varietal Resistance Very little is known about resistance of spinach varieties to Fusarium wilt, but differences in susceptibility of parent (inbred) lines to Verticillium wilt have been detected in spinach seed crops.
- Avoid planting on soil known to be infested with V. dahliae.
- Do not plant spinach in consecutive years. Long rotations out of spinach seed crops may be necessary for susceptible parent (inbred) lines.
- Avoid planting spinach seed crops immediately following potato crops.
- The disease appears to be more severe on alkaline soils.
- If possible, minimize moisture stress to spinach seed crops during flowering and seed set.
- Mertect at 0.006 mg ai/seed plus a dye. To control seedborne fungi.
- Topsin M WSP at 8 oz/100 lb seed plus a dye on spinach grown for seed only. Oregon (SLN OR-150012b) and Washington only (SLN WA-090003b).
References du Toit, L.J., Derie, M.L., and Hernandez-Perez, P. 2005. Verticillium wilt in spinach seed production. Plant Disease 89:4-11.
Villaroel, M.I., du Toit, L.J., and Correll, J.C. 2007. Screening for resistance to Verticillium dahliae in spinach. Phytopathology 97:S118