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University of Minnesota Extension

Cucurbit viruses

Quick facts

  • Viral infections commonly occur on all cucurbit crops in Minnesota.
  • Virus-infected leaves often have a mottling or mosaic pattern in shades of green and yellow. It is difficult to identify the specific virus from visual symptoms alone. Submitting samples to a plant disease clinic is the only way to confirm the species.
  • Certain perennial weeds allow viruses to survive from season to season in a field. Aphids then transfer the virus to cucurbits.
  • There are no pesticides available to reverse or limit the symptoms of viral infection.
Cucurbit leaves infected by virus, yellowing of leaves
Distorted, discolored squash leaves due to a virtual infection

Telling viruses apart from other plant issues

It is difficult to identify a virus by symptoms alone. Symptoms vary depending on the crop, variety, age of the plant at the time of infection, and in some cases weather. 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 identify 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 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 abnormally small. Growth on infected vines is typically stunted. In the case of cucumber mosaic virus (CMV) infections, the vines may wither completely.
  • The virus's effect on fruit depends on when it infected the plant. 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 off-coloration on all or part of the fruit. Melons infected with squash mosaic virus (SqMV) often lack netting at maturity.
Two pumpkins in a pile, both with circles and spots of discoloration.
Pumpkins infected with a mosaic virus
Yellow search with green spots caused by a mosaic virus.
Yellow squash infected with a mosaic virus


  • Specific cucurbit viruses include 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).
  • 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 rudbeckia, and a wide variety of weeds.
    • All of the mosaic viruses can also infect weeds in the cucurbit family.
  • These viruses, with the exception of SqMV, are transferred by aphids.  Not all aphids carry viruses.  Aphids that feed on infected weeds and crops pick up the virus, and as they move on and feed on other plants, spread the virus.
  • SqMV is transmitted by both striped and spotted cucumber beetles.
  • Perennial weeds allow the virus to survive from season to season in a field.
  • Viruses can transfer from plant to plant on the hands and tools of workers through infected sap.
  • Once in the plant, viruses move systemically through the tissue, infecting leaves, vines and fruit.
  • Squash mosaic virus can be introduced on infected seed. The other mosaic viruses rarely transfer on seed

Managing cucurbit viruses in the home garden


Managing cucurbit viruses on farms


Authors: Marissa Schuh, horticulture IPM Extension educator, and Michelle Grabowski
Reviewed by Annie Klodd, Extension educator - fruit and vegetable production

Reviewed in 2021

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