By L.J. du Toit and C.M. Ocamb
Cause Cucumber mosaic virus (CMV), a pathogen spread by insects such as aphids and cucumber beetles and mechanically by cultivation and handling. CMV overwinters in seeds of wild cucumber and in wild perennial milkweed, ground cherry, and matrimonial vine. It also has a wide range of vegetable crop hosts. Epidemics often are associated with unusually high temperatures. Isolates of CMV in spinach belong to serogroup I or serogroup II. CMV serogroup II isolates can be seedborne and seed-transmitted in spinach. Rates of seed transmission are relatively low (<2%) for most varieties, but seed transmission can be >20% for some varieties. CMV can also be carried by spinach pollen. Therefore, infected male or female spinach plants can serve as a source of inoculum for infection of seed in spinach seed crops.
Symptoms A yellow and green leaf mottle and mild leaf distortion. The margins of infected leaves may role downwards. Infected plants can be stunted. Symptoms are more severe the younger the age at which spinach plants become infected.
- Remove wild cucumber vines, milkweed, and other susceptible weed hosts within 1000 ft of the field, if possible.
- Resistant varieties are available from most seed companies.
- Do not grow spinach near highly susceptible vegetables such as cucurbit crops and tomatoes.
- Rogue symptomatic male and female spinach plants from spinach seed crops to avoid infection of the seed to be harvested.
- For spinach seed crops, stock seed lots of parent lines should be tested for CMV serogroup II.
Chemical control Control aphids by spraying and dusting. See the PNW Insect Management Handbook for details.
References du Toit, L.J., Brown, P.R., Derie, M.L., and Bentley, T. 2007. Cucumber mosaic virus survey in spinach seed crops in the Pacific Northwest, USA. Phytopathology 97:S30.
Yang, Y., Kim, K.S., and Anderson, E.J. 1997. Seed transmission of Cucumber mosaic virus in spinach. Phytopathology 87:924-931.