Friday, August 12, 2011

Squash viruses

Several viruses affect squash including squash mosaic virus and cucumber mosaic virus. Aphids transmit the viruses from infected plants that can include weeds such as common lambsquarters, kochia and others.

You may discover viruses as we did recently in our yellow zucchini planting by spotting one plant with light green, mottled leaves in a sea of healthy. dark green leafed plants. (Click photo to enlarge). Leaves often have a mosaic pattern and may be distorted, have deep lobes, or appear string like and thin.

Fruit can appear small, deformed, mottled, have ring spots or exhibit color breaks and may develop warts. In our planting the affected fruit (photo left) look quite different than normal yellow zucchini (photo right). The different viruses produce different symptoms depending on the stage in which the plant is affected and several viruses can affect the same plant.

Do plant virus resistant or tolerant varieties when available. Purchase seed from a reputable supplier and use care in saving seed. Manage aphids to keep numbers low. As soon as diseases appears, remove plants like we did. Viruses can be mechanically transmitted so wash hands and tools before working with healthy plants. Control nearby weeds that may harbor viruses. There are no pesticides to control viruses.

Photo credit: Virus mottled leaf plant stands out, Virus distorted fruit, Normal yellow zucchini fruit - all Carl Wilson


  1. Quick question....I have two zucchini plants which appear quite healthy, however the fruit keep turning yellow and falling off before they get bigger than an inch or two. I've never had this problem in the past. Any suggestions?

  2. Squash bugs are gray with red eggs. Late season feeding does not generally affect yield or quality. How close are the butternut and spaghetti squash to harvest? If they are reasonably mature, the insects may not be an issue. For more information on squash bugs see