Watermelons With Cucurbit Yellow Vine Disease – What Causes Yellow Watermelon Vines

By Darcy Larum, Landscape Designer

In the late 1980s and early 1990s, a destructive disease spread through crop fields of squash, pumpkins and watermelons in the United States. Initially, the disease symptoms were mistaken for fusarium wilt. However, upon further scientific investigation, the disease was determined to be Cucurbit Yellow Vine Decline, or CYVD for short. Continue reading to learn about treatment and control options for watermelons with cucurbit yellow vine disease.

Watermelons with Cucurbit Yellow Vine Disease

Cucurbit yellow vine disease is a bacterial disease caused by the pathogen Serratia marcescens. It infects plants in the cucurbit family, such as melons, pumpkins, squash and cucumber. The symptoms of yellow vine disease in watermelons are bright yellow vines, which seemingly appear overnight, foliage that rolls up, runners which grow straight up, and rapid decline or dieback of plants.

Roots and plant crowns may also turn brown and rot. These symptoms usually appear on older plants just after fruit set or shortly before harvest. Young infected seedlings may wilt and die quickly.

What Causes Yellow Watermelon Vines

Cucurbit yellow vine disease is spread by squash bugs. In springtime, these bugs come out of their winter bedding grounds and go into a feeding frenzy on cucurbit plants. Infected squash bugs spread the disease to each plant they feed upon. Younger plants are less resistant to the disease than older plants. This is why young seedlings may wilt and die immediately while other plants can grow most of the summer infected with the disease.

CYVD infects and grows in the plant’s vascular system. It grows very slowly but, eventually, the disease disrupts the flow of the plant’s phloem and symptoms appear. Watermelons with cucurbit yellow vine disease weakens plants and can make them more susceptible to secondary diseases, such as powdery mildew, downy mildew, black rot, scab, and plectosporium blight.

Insecticides to control squash bugs can be used in spring at the first sign of their presence. Be sure to read and follow all insecticide labels thoroughly.

Growers have also had success in using trap crops of squash to lure squash bugs away from melons. Squash plants are the preferred food of squash bugs. Squash plants are planted around the perimeters of other cucurbit fields to draw squash bugs to them. Then the squash plants are treated with insecticides to kill the squash bugs. In order for trap crops to be effective, they should be planted 2-3 weeks before watermelon crops.

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