Be on the Look-out For a New Whitefly-Transmitted Virus on Cucurbits (May 27, 2015)

Last fall, researchers from the University of California discovered pumpkin plants on the UC Research Center in Holtville that showed signs of viral infection (severe stunting, leaf yellowing, and leaf curling) associated with high populations of whiteflies. Through a series of laboratory tests, they found the plants were infested with a virus similar to Squash vein yellowing virus (SqVYV), a Bemisia whitefly transmitted ipomovirus (family Potyviridae). It is not clear where the ipomovirus originated and fortunately since the initial discovery, subsequent sampling of melons this spring has yielded no further infected plants. So why is this important? If this ipomovirus were to spread throughout the region it could pose a threat to melon production in the desert southwest, particularly on watermelons in years when whitefly populations are high during the spring. SqVYV was first identified from squash and watermelon in Florida in 2005, and had been causing serious decline of watermelon vines since 2003. To date, Florida is the most economically impacted area by SqVYV, but the virus has also been detected in Indiana and South Carolina. As noted above, whiteflies (Bemisia tabaci b-biotype) acquire SqVYV in semi-persistent manner, and appear to retain the virus for only 24 hr after leaving infested plants. In commercial watermelon production, symptoms of SqVYV vine decline are usually first noticed at or just before harvest when whitefly populations are allowed to build up. Symptoms include yellowing, scorched or brown leaves, defoliation and wilting of the vines, and a rapid collapse of mature vines. The interior of the mature fruit rind can be discolored (brown areas under the rind), rendering the fruit unmarketable. Early symptoms on watermelon include yellowing and downward curling of the new growth. Based on reports from Florida, muskmelon (Cucumis species) are not very susceptible to SqVYV. To date, the host range of SqVYV appears to be limited only to cucurbit crops and weeds. For more information on this virus visit these publications: Recommendations for Management of Whiteflies, Whitefly-transmitted viruses, and Insecticide Resistance for Production of Cucurbit Crops in Florida and A new and potentially damaging whitefly-transmitted virus of cucurbits was found this fall 2014 in Imperial County, CA. If you experience vine decline near or during watermelon harvest or observe any unusual symptoms on melons, please contact us.

Remember, When in Doubt . . . . . “SCOUT”