Why viruses are the biggest threat to your cucurbits

There are ways to prevent or cure most cucurbit diseases, but there's no known way to cure a virus once it has infected the plant, warns Bill Kerr.

A number of viruses infect cucurbits Aeron but only four do the rounds in South Africa:

• Cucumber mosaic virus CMV); 
• Zucchini yellow mosaic virus ZYMV);
• Papaya ringspot virus PRSV); and
• Watermelon mosaic virus WMV).

The season may start off with no problems, but as time passes, the threat increases, because the vectors for these viruses are aphids. Thanks to wind currents, aphids can move over great distances, and many species can transmit viruses.

Some viruses can also be spread mechanically by workers and farm implements.

In the case of baby marrows, growers of this crop should be aware of how fast zucchini yellow mosaic virus can spread once harvest commences.

Baby marrows are commonly harvested with a knife to prevent damage to the petiole, but this method can spread the virus rapidly. It’s better to pick by hand and trim by knife afterwards.

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