Vector Transmitting Red Blotch Virus Found

Vector Transmitting Red Blotch Virus Found

A vine shows signs of red blotch along a leaf. (Frank Zalom)

A vine shows signs of red blotch along a leaf. (Photo credit: Frank Zalom)

Researchers at the University of California, Davis (UC-Davis) have found the vector that seems to be spreading grapevine red blotch, a major step toward controlling the disease.

A virus known as grapevine red blotch-associated virus (GRBaV) was discovered in vineyards planted with red wine grape cultivars in Napa County in 2008. It creates a disease on vines that presents as red blotches that start on leaf margins or blades and continue onto primary and secondary veins. In white grape cultivars, the blotches appear white or pale yellow.


The effects vary based on cultivars, but vines infected by red blotch have reduced total soluble solids in juice. Titratable acidity and pH can also be affected.

But a team of scientists has discovered that the three-cornered alfalfa treehopper (Spissistilus festinus) carries and is able to transmit the virus that causes red blotch.

“We still have to confirm transmission in the field, but we have some indications now that we have the vector,” said Frank Zalom, Distinguished Professor of Entomology at UC-Davis, who made the discovery with post-doctoral researcher Brian Bahder and USDA virologist Mysore “Sudhi” Sudarshana.

Zalom said there are several other insects that carry the grapevine red blotch-associated virus, but it hadn’t been clear whether one of those insects, a nematode or some other method of transmission, delivered it to grapevines. The team was able to show the three-cornered alfalfa treehopper could transmit the virus in a lab setting. Now the team members will set out to show the same result in a field trial.

“There is a good indication that we’ll be able to repeat that in the field,” Zalom said.

Knowing how the virus is transmitted is key to stopping red blotch’s spread. Zalom said another research path will focus on how to manage three-cornered alfalfa treehoppers.

A grower with a vineyard that has signs of red blotch should flag vines and have them tested by a commercial laboratory. If present, growers will need to decide whether to remove those vines and plant new vines. There is no current method for curing vines infected with red blotch.