Cucurbit Yellow Stunting Disorder Virus Cases Flaring In South Florida
May 21, 2016 
Photo by Gene McAvoy
Disease Specs
Cucurbit yellow stunting disorder virus (CYSDV) is a crinivirus, which primarily affects cucurbits including melons, watermelon, and squash. CYSDV was found in Florida in 2007. It has been sporadic and low level in occurrence, but appears to have become more common in South Florida this spring.
Identification
Infected cucurbit plants initially show a chlorotic yellow spotting, which eventually develops into an interveinal chlorosis where the veins remain green but the rest of the leaf turns yellow. Older leaves on infected plants may shrivel and die. In some instances, vines might collapse rapidly as plants approach maturity.
Fruit on infected plants may appear normal, but often have reduced levels of sugars and don’t ship or store well, which can affect marketability and result in economic loss.
Symptoms of cucurbit yellow stunting disorder virus can be confused with abiotic factors, such as nutrient deficiency.
Survival And Spread
The virus is spread exclusively by the whitefly vector, Bemisia tabaci. All biotypes transmit the virus efficiently and can remain infective for up to nine days. Whitefly transmission is entirely responsible for virus spread over short distances within and between fields. The virus is not transmitted mechanically nor is it seedborne. It does not take many whiteflies to spread the virus.
CYSDV is spread over long distances through the movement of infected transplants. Since it can take three to four weeks for disease symptoms to develop following infection, infected symptomless plants can be unknowingly transported. The virus also can be moved long distance by virus-carrying whiteflies that may accompany transported plant material such as cucurbits and other susceptible infected plants with or without symptoms. Because whiteflies can be blown long distances with high winds, the virus may be transported in this manner as well.
Management Methods
Control is difficult because there is no chemical or biological control to fight the virus. Currently, no varieties resistant to CYSDV are available. Managing whiteflies and hosts of the virus are the only options for reducing losses at this time. Use virus- and whitefly-free transplants.
Sanitation is very important and growers should destroy old infested fields soon after harvest is complete.
Practice good weed management in and around fields to eliminate any cucurbit weeds or volunteers that could serve as a source of viruses and whiteflies for the crop.
Separate fall and spring cucurbit crops in time and space to create a cucurbit free period.
Do not plant new crops near or adjacent to old, infested crops confirmed to be infected by the virus.
Apply a soil application of a neonicotinoid insecticide at transplanting.
Monitor whitefly populations throughout the growing season and apply insecticides as needed. Rotate insecticides with different modes of action to minimize development of insecticide resistance.
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