What is Red Blotch Disease?
Red Blotch Disease is caused by a virus known as grapevine red blotch virus (GRBV). It was first described on Cabernet Sauvignon in Napa Valley in 2008 but has since been identified in many US wine production regions, including CA, ID, NC, NY, MO, OH, OR, and WA. There are 86 different viruses known to infect grapevines, more than any other perennial crop, and GRBV is only one of them. Although recently identified, GRBV has likely been present for decades. The disease causes canopies to become red and blotchy (in red fruited varieties) or chlorotic and yellow (in white fruited varieties). The disease may delay or hamper fruit ripening, causing reduced wine quality for some varieties and in some regions. Additional symptoms descriptions are available in the further reading section below.
Does the disease spread?
Pathologists believe that an insect vector may spread GRBV, but none has been found to cause spread in commercial vineyards. However, the Three-Cornered Alfalfa Hopper and Virginia Creeper Leafhopper were shown to transmit the virus in lab/greenhouse studies. Further studies continue across the US to investigate other treehopper and leafhopper species and other insects found in and around GRBV-infected vineyards to determine which may be causing virus spread. We do not recommend insecticide use at this time for the purpose of reducing these insect populations in and around infected vineyards. Humans are the only confirmed vector to date, as the most common virus spread is occurring with the use of virus-infected plant material during propagation and planting.
Prevention and Monitoring
The best recommendations to date are to avoid the virus by using "clean" plant material (bud wood or plants). You can obtain clean plants by way of a certification program (certified stock) or sourced from plants that have been rigorously tested and confirmed free of virus. Below are considerations for preventing the virus in vineyards:
- New vineyard plantings: When establishing a new vineyard, buy only certified (or virus tested) plants. Be sure to inquire with the nursery or supplier as to whether the plants you are buying are certified and/or have been tested for GRBV or other important viruses. Certification refers to vines originating from a virus-free mother block that was established with vines from an official state certification program.
- Grafting over: When grafting a new cultivar in an established vineyard, be sure to source clean bud wood by purchasing certified (virus free) bud wood and/or test source vineyards for virus. Secondly, ensure that the vines you are grafting are not infected by testing the vines for virus. Grapevine virus testing is available at commercial labs (see list below).
- Observed virus: If you suspect that your vineyard has virus, mark and monitor symptomatic vines. Symptoms typically are visible during late summer to fall. Take detailed notes on when you first observe symptoms (date and the vine growth stage), monitor, and record changes in symptoms over time. Test symptomatic vines for virus by submitting tissues for analysis. It is also good to test asymptomatic vines in the same block to determine if there may be healthy vines present as well. See virus-testing labs below, and check the lab sampling protocols before collecting and submitting samples. Researchers note that it is best to use dormant tissue in winter, selecting basal cane positions near the cordon/cane/trunk for testing. Sampling dormant tissues during winter will give you the greatest opportunity to detect the virus if it is present. Sampling of leaf tissue early in spring or summer (even late summer) will have high likelihood of not detecting the virus, resulting in false negative results.
- Confirmed virus: If you have infected vines, consider removing them, especially in young plantings. Early detection and plant removal in young vineyards has been shown to reduce the spread of virus. Before removing infected vines, consider the economic impact for your vineyard. The article by Ricketts et. al 2017 in the American Journal of Enology and Viticulture has economic-based rogue and replant scenarios.
- Testing for virus: When testing plants for virus, it is important to test for multiple viruses (often are called "virus panels" by testing labs). This is highly recommended to determine which virus may be causing issues, as there several viruses that may cause similar symptoms (e.g. Leafroll (GLRaV)).
Virus testing labs on the West Coast (alphabetical order)
- AL&L Lab
- California Seed & Plant Lab
- Eurofins STA Laboratories
- OSU Plant Clinic
- WSU Virus Diagnostic Lab
See the resources below for further information about the disease.
- Grapevine Red Blotch Disease- Oregon Department of Agriculture
- Red Blotch Information Fact Sheet- National Clean Plant Network
- Grapevine Red Blotch Disease- PNW Plant Disease Handbook
- Increasing Accuracy of Sampling for Red Blotch Disease - Dr. Achala KC, Plant Pathologist, OSU
Red Blotch Research
Use the resources below to learn more about the research in progress on Red Blotch Disease and its vectors.
- Oregon Wine Research Institute Red Blotch Study Team
- Grapevine Red Blotch – What You Need to Know (webinar)
- California Department of Food and Agriculture research proceedings (include Red Blotch research reports in 2015-2018)
- UC-Davis Research Team working on Three-Cornered Alfalfa Hopper
Below are published, open-access research articles about Red Blotch Disease in Oregon: