Do Your Best To Stay Ahead of Watermelon Vine Decline
December 25, 2021 
A team of researchers from the University of Florida, Florida Department of Citrus, and the USDA-ARS discovered that watermelon vine decline was caused by a whitefly-transmitted virus, which they called squash vein yellowing virus.
Photo by Dr. Scott Adkins
Since it was first observed in 2003, watermelon vine decline has caused severe monetary losses to growers in Florida.
We asked Gene McAvoy, Emeritus UF/IFAS Vegetable Extension Agent and longtime Florida Grower® magazine contributor, about the disease and management tactics.
What are the symptoms of watermelon vine decline?
McAvoy: Symptoms of watermelon vine decline include a slight internal yellowing of stem tissue in the crown area, wilting vines, scorched and brown leaves, defoliation, and rapid mature vine collapse. Frequently, fruit are observed with greasy necrosis (brown) on the interior portion of the rind that render the fruit unmarketable.
What kind of damage can this disease do to watermelon?
McAvoy: Watermelon vine decline strikes as the crop approaches harvest or soon after first harvest. Disease progress is rapid. Symptoms may develop and affect more than 80% of the crop within a week to 10 days. Fruit quality is greatly reduced by the disease.
Gene McAvoy
Are there any suggestions on scouting for the disease?
McAvoy: The watermelon vine decline virus is transmitted by the silverleaf whitefly. Monitor the crop regularly for the presence of adult whiteflies.
What cultural practices should growers deploy to reduce the likelihood of disease?
McAvoy: Sanitation is important. Growers should strive to eliminate any cucurbit weeds and promptly and efficiently destroy crops within five days of final harvest to decrease whitefly numbers and sources of viruses. It is best to destroy crops block-by-block as harvest is completed rather than waiting and destroying the entire field at one time.
Other cultural practices that will help reduce the likelihood of vine decline include separating fall and winter cucurbit crops in time and space and avoiding planting new crops near or adjacent to old, infested crops. Delay planting new fall crops as long as possible and remove spring crops as early as possible to increase the summer crop-free period and avoid carryover of disease and pests.
What are some management options for controlling the disease?
McAvoy: Management is similar to that of other whitefly-transmitted viruses in vegetable crops — such as tomato yellow leaf curl virus in tomato — and consists of a combination of techniques aimed at keeping whitefly numbers low. These practices will help delay the initial whitefly infestation and slow the introduction of viruses into the crop. Use a soil-applied systemic insecticide at planting for whitefly control. If foliar applications of neonicotinoids are applied instead of soil drenches at transplanting, these should be restricted to the pre-bloom applications because of potential toxicity to bees. Use of UV-reflective mulches, which repel migrating whiteflies in the first few weeks of the crop, may help delay the introduction of virus.
Subscribe Today For
