Back to Diseases of cucurbits
Infection with virus commonly occurs on all cucurbit crops in Minnesota. These diseases are caused by several different viruses including Cucumber Mosaic Virus (CMV), Squash Mosaic Virus (SqMV), Zucchini Yellow Mosaic Virus (ZYMV), Watermelon Mosaic Virus 2 (WMV-2) and Watermelon Mosaic Virus 1 (WMV-1) also known as Papaya Ringspot Virus (PRSV).
It is difficult to distinguish between the different viruses by symptoms alone. Symptoms vary depending on the crop, variety, age of the plant at the time of infection and in some cases weather. In addition it is common to find plants infected with more than one virus at the same time, often resulting in combined severe symptoms. The best way to distinguish between the different viruses is through analysis of a sample at the University of Minnesota Plant Diagnostic Clinic.
Virus infected leaves often have a mottling or mosaic pattern in shades of green and yellow. This mosaic can be very distinct and obvious or fairly subtle. Leaves are often distorted or deformed. They may be puckered, cupped under, have deep lobes, or appear thin and string-like. Young leaves often show the most severe symptoms and are frequently abnormally small. Growth on infected vines is typically stunted and in CMV infections, vines may wither completely.
The virus's affect on fruit varies depending on when the plant was infected. Early infections often result in no or very low fruit production. Later infection can result in fruit that is small, deformed and discolored. Fruit may have a mottled or mosaic pattern, ring spots or exhibit color break on all or part of the fruit. Melons infected with SqMV often lack netting at maturity.
All of the mosaic viruses can infect all of the cucurbit crops including melon, cucumber, pumpkin, summer and winter squash. In addition, many of the mosaic viruses can also infect common weeds. Squash mosaic virus will infect weeds in the Chenopodiaceae family like common lambsquarters, maple leaf goosefoot, Russian thistle and kochia. Watermelon mosaic virus infects legumes like clover. Cucumber mosaic virus can infect plants from over forty families, including vegetable crops like tomato, lettuce and spinach, flower crops like gladiolus, petunias, impatiens and rudbekia and a wide variety of weeds. All of the mosaic viruses can also infect weeds in the cucurbit family.
Most viruses that infect cucurbits are transferred by aphids with the exception of SqMV which is transmitted by both striped and spotted cucumber beetles. Aphids feed on virus infected plants (weeds or crop) and then transfer the virus when they feed on a new plant. Perennial weeds allow the virus to survive from season to season in a field. Viruses can also be transferred from plant to plant on the hands and tools of workers through infected sap. Squash mosaic virus can come in on infected seed. The other mosaic viruses are only rarely transferred on seed.
Once in the plant, viruses move systemically through the tissue infecting leaves, vines and fruit.
- Plant resistant or tolerant varieties whenever available. Resistance is virus specific and it is necessary to first determine which mosaic virus is causing disease in order to select appropriate viruses.
- Purchase clean seed from a reputable supplier. If saving seeds, do not collect seed from infected plants.
- Control weeds within and around the field. Especially focus control efforts on perennials weeds that may allow the virus to carry over from one season to the next.
- Manage aphids and cucumber beetles to keep populations low.
- If disease appears in a few plants, rogue and bury these plants to prevent further spread of the disease.
- Clean tools and workers hands with soap and water after working with infected plants. Reduce maintenance tasks that require handling of infected plants as much as possible.
- In greenhouse or hoop house production, use screening and other methods to exclude aphids. Eliminate weeds or other virus hosts within 350 feet of the greenhouse or hoop house. Avoid planting cucurbit field crops next to hoop house or greenhouse production areas.
- There are no pesticides that can be applied to reverse or limit the symptoms of viral infection.