The only way to positively confirm which disease is present, or whether a sample contains both, is through laboratory molecular testing, Adkins says.
“At this point, I’d say it’s based on where you’re located,” he says. “If you’re on the peninsula and you see strong TSWV symptoms, I’d suspect GRSV. In South Carolina, people wouldn’t give GRSV a second thought” because TSWV is common.
Thrips spread the virus
Western flower thrips are a confirmed vector of GRSV, Adkins says.
The larvae, or immature thrips, pick up the virus as they feed on infected plants. They remain infectious when they reach adulthood and transmit the virus as they feed on healthy plants.
This is the same infection mechanism that occurs with Western flower thrips and tomato spotted wilt virus.
One of the goals of the multi-state research project is to conduct tests to determine whether other thrips, such as common blossom or yellow flower thrips (Frankliniella schultzei), melon thrips (Thrips palmi) or chilli thrips (Scirtothrips dorsalis), also can vector GRSV, he says.
Mellinger says there’s strong circumstantial evidence that points to F. schultzei also being a vector of GRSV.
In the Homestead area, he found tomato fields with higher GRSV incidence adjacent to watermelon fields with high populations of F. schultzei.
GRSV management strategies
Although little is known about GRSV, Adkins says he surmises that the same management techniques growers use for TSWV would probably help control GRSV.
Those include starting with clean transplants, applying a systemic insecticide at planting, using metallized mulch on planting beds, using selective insecticides to preserve beneficial insects and using TSWV-resistant tomato varieties with the Sw5 gene.
The Sw5 gene also appears to impart resistance to GRSV, Adkins says, citing research results.
For more information on GRSV, download the University Florida EDIS PP282 at http:// edis.ifas.ufl.edu/pp282.