Vine Decline in Florida

For several years, Florida watermelon growers have struggled with a late season vine decline disease.  It is especially devastating financially as all inputs, including harvest in some cases, have been made to the crop at the time the disease becomes noticeable.  Infection rates can rapidly increase from 10 to greater than 80 percent within one week.  Now, recent research published in Phytopathology addresses the cause of this disease, which appears to be the result of viral infection of the plant. 

Researchers from UF/IFAS, USDA, and the Florida Department of Agriculture and Consumer Services collaborated on studies to elucidate the nature of this disease.  During a survey in Hillsborough County in 2003, a sample was collected from a squash plant expressing vein yellowing.  This sample, one of forty taken from the same field, was found to be infected with a virus not previously described in Florida.  It is described as a flexous rod-shaped virion of approximately 840 nm in length.  The proposed name for the virus is Squash vein yellowing virus (SqVYV). 

The host range (which excludes the Amaranthaceae, Apocynaceae, Asteraceae, Chenopodiaceae, Fabaceae, Malvaceae, and Solanaceae), coupled with analysis of its transmission (tested with both whiteflies and aphids), suggest that it is a whitefly-transmitted member of the genus Ipomovirus in the family Potyviridae.  Although originally obtained from squash plants, the researchers were able to induce the watermelon vine decline disease and associated fruit necrosis in the greenhouse. 

What this means to growers in terms of pest management is clear.  As with many other vegetable crops in Florida, a serious whitefly-vectored disease places this pest into the primary category, with much less tolerance for its residence in the field.  Consequently, more growers will probably be applying a neonicotinoid insecticide to their watermelon crop.  This places more pressure on this group of materials, and anyone that is dealing with these must be aware of pesticide resistance and the UF/IFAS researchers associated with this topic.  Dr. Lance Osborne and Dr. David Schuster are both involved in the whitefly biotype and pesticide resistance issues.  Within counties, Eugene McAvoy is also a lead investigator.  Please interact with these programs if you have whitefly/virus concerns.  A good Web site to start with in addressing plans to combat these problems is: http://www.mrec.ifas.ufl.edu/LSO/bemisia/vegetable.htm  (Phytopathology, 97:145-154).