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Squash (Cucurbita spp.) - Virus Diseases
Cause Several viruses can cause a mosaic symptom including cucumber mosaic virus (CMV), zucchini yellows mosaic virus (ZYMV), and watermelon mosaic virus 2 (WMV2). Each is spread by aphids, and CMV also may be spread by cucumber beetles. CMV overwinters in wild cucumber seed and in wild perennial milkweed, ground cherry, and matrimonial vine.
Symptoms CMV-leaves are markedly mottled and wrinkled with yellow and green blotches and edges cupped down. Early-season infection dwarfs the plant; later infections show the typical mosaic symptoms only on late-season growth following infection. Fruit develops raised wart-like bumps with pale, whitish green areas between, and it tastes bitter. Some varieties of small, later fruit have a pale greenish white appearance.
Cultural control
- Remove all infected vines.
- Remove wild cucumber vine, milkweed, and other susceptible weed hosts within 1000 ft of the field if possible.
- Control aphid vectors. See the PNW Insect Management Handbook for details.
- Avoid unnecessary field activity, which can spread the virus.
- In slicing cucumber varieties, Niagara is resistant; there is also some tolerance to the virus in Dasher II, Multipik, Burpee, Surecrop, Gemini, Marketmore, and Sensation. For pickling cucumbers, the varieties, MR-17, SMR-18, SMR-58, and Pioneer, have high tolerance and are recommended for planting.