# Grapevine red blotch

- URL: https://backyardgrapes.com/diseases/red-blotch/
- Scientific name: Grapevine red blotch virus (GRBV)
- Category: Viral
- Affects: Leaves
- Severity: moderate
- Favored by: Spread mainly through infected planting material; an insect vector (three-cornered alfalfa hopper) is implicated.
- Easily confused with: Grapevine leafroll, Grapevine fanleaf virus, Potassium deficiency

**Summary:** Red blotches on leaves that mimic leafroll but mainly delay ripening and lower sugar.

**What to look for:**
- Irregular red blotches across the leaf blade on red varieties, often with the main veins turning pink or red.
- Yellow/pale blotching instead of red on white varieties.
- Delayed, uneven ripening; low sugar (Brix) and poorly balanced fruit.
- Symptoms strongest late in the season, generally from the base of the shoot upward.

**Treatment — Cultural / prevention:**
- Buy certified clean, tested planting stock — the disease travels in infected vines.
- Test suspect vines and remove confirmed infected ones to protect the rest.
- Source from reputable nurseries; don't propagate from symptomatic vines.

**Treatment — Organic / low-toxicity:**
- No cure exists — clean stock and roguing are the strategy.

**Treatment — Conventional (chemical):**
- None directly; vector management is still being researched.

Grapevine red blotch is a relatively recently identified virus that has spread widely
through nursery stock. On the surface it looks a lot like leafroll — red blotches on the
leaves of red varieties late in the season — but there are differences: red blotch often
reddens the main leaf veins (leafroll typically leaves them green), and the leaf margins
don't roll downward as strongly.

What makes it costly isn't the leaves but the fruit: infected vines ripen late and never
reach full sugar, so the crop stays sour and unbalanced. Because the virus is carried in
planting material, the practical defence for a home grower is the same as for the other
grape viruses — start with certified clean vines and remove any vine that tests positive.

**Image credits:**
- A leaf from a Merlot grapevine shows red veins and red blotches on margins and interveinal regions, typical symptoms of red blotch disease — [Photo: Washington State University, Oregon Wine Press](https://www.oregonwinepress.com/beating-red-blotch)
- Grape leaf with reddish-purple blotches caused by grapevine red blotch virus; tested negative for leafroll and positive for red blotch — [Photo: OSU Plant Clinic Image, 2013, Pacific Northwest Pest Management Handbooks](https://pnwhandbooks.org/plantdisease/host-disease/grape-vitis-spp-grapevine-red-blotch-disease)
- Red blotch disease symptom on a Pinot noir vine, with red-blotched leaves and clusters near harvest — [Oregon State University Extension Service](https://extension.oregonstate.edu/crop-production/wine-grapes/how-protect-vineyards-grapevine-red-blotch-disease-grbd)

**Sources:**
- [How to protect vineyards from grapevine red blotch disease (GRBD)](https://extension.oregonstate.edu/crop-production/wine-grapes/how-protect-vineyards-grapevine-red-blotch-disease-grbd) — Oregon State University Extension Service
- [Grape (Vitis spp.)-Grapevine Red Blotch Disease](https://pnwhandbooks.org/plantdisease/host-disease/grape-vitis-spp-grapevine-red-blotch-disease) — Pacific Northwest Pest Management Handbooks (OSU/WSU/UI)
- [Grapevine red blotch disease: A comprehensive Q&A guide](https://pmc.ncbi.nlm.nih.gov/articles/PMC10569545/) — PLoS Pathogens (PMC)
- [Grapevine Red Blotch-Associated Virus](https://www.ncipmc.org/communications/pest-alerts/grapevine-red-blotch-associated-virus/) — North Central Integrated Pest Management Center