Backyard Grapes Identify & treat grapevine problems
Viral moderate severity

Grapevine red blotch

Grapevine red blotch virus (GRBV)

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

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
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
Red blotch disease symptom on a Pinot noir vine, with red-blotched leaves and clusters near harvest Oregon State University Extension Service

Description

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.

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 options

Cultural & prevention

Start here — habits that stop problems before they spread.

  • 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.

Organic / low-toxicity

Gentler sprays and biologicals for active outbreaks.

  • No cure exists — clean stock and roguing are the strategy.

Conventional fungicide / pesticide

For severe cases. Always follow the product label.

  • None directly; vector management is still being researched.

Sources

This entry is based on the references below. Read them for full detail and for spray timings and rates valid where you live.

  1. How to protect vineyards from grapevine red blotch disease (GRBD) — Oregon State University Extension Service
  2. Grape (Vitis spp.)-Grapevine Red Blotch Disease — Pacific Northwest Pest Management Handbooks (OSU/WSU/UI)
  3. Grapevine red blotch disease: A comprehensive Q&A guide — PLoS Pathogens (PMC)
  4. Grapevine Red Blotch-Associated Virus — North Central Integrated Pest Management Center