Squash mosaic virus (SqMV)
Striped cucumber beetle (Acalymma spp.)
Spotted cucumber beetle (Diabrotica spp.)
This disease is most important on cantaloupe, pumpkin and squash; however, some strains of the virus infect watermelon. Reports on commercial cucumbers have been limited, but infections are sporadically reported in breeding programs.
Melon and Squash: Green vein banding of the first or second leaf may develop in seedlings grown from squash mosaic-infected seed. Young leaves may be symptomless or may exhibit yellow spots, vein clearing and/or blistering. Leaves can be severely distorted, with marginal projections from the veins giving a fringe-like appearance to the leaf margin. Infected plants are stunted with fewer branches and fruit. Fruit may develop mild mottling to severe deformation. Netted melon types infected with SqMV may not form netting.
Cucumber: Leaves may exhibit chlorotic spots with an upward leaf curl, systemic vein-clearing or a yellow vein-banding, which may become necrotic. As the crop ages, additional symptoms on the new foliage may not be apparent and symptom expression decreases as temperatures increase, making visual identification difficult.
Watermelon: Necrotic local lesions may develop, but SqMV is generally not of economic importance on watermelon.
CONDITIONS FOR DISEASE DEVELOPMENT
Infected seed is often the initial source of SqMV infection. The striped cucumber beetle and the spotted cucumber beetle are the primary vectors, can acquire the virus after just five minutes of feeding, and transmit the virus for 5–20 days. The virus can also be mechanically transmitted by workers and equipment. Grasshoppers may also transmit SqMV, although they are not a major vector of the virus.
Use virus-free seed or transplants, control the vectors, remove cucurbit volunteers and weeds, implement sound sanitation practices and remove or deep-plow infected crop debris.