Backyard Grapes Identify & treat grapevine problems
Disorder moderate severity

Sunburn & sunscald

Heat and intense sun scorching exposed berries and leaves — often triggered by over-thinning the canopy.

Sunburned green grape berries with brown, sunken patches on the exposed side of a cluster Photo: Sandra Julian American Vineyard Magazine
Brown, sunken sunscald patches on the exposed side of green berries Photo: Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org Bugwood.org CC BY-NC 3.0 US
Chardonnay cluster with sunburn scald and raisined berries Photo: Agne27 Wikimedia Commons CC BY-SA 3.0
Sunburned Riesling grapes: a cluster with shrivelled, browned berries next to unaffected berries Photo: Joanna Gambetta SevenFifty Daily

Description

Sunburn isn’t caused by any pathogen — it’s heat and ultraviolet light cooking exposed tissue — but it lands on this list because growers so often mistake the brown, sunken patches on berries for a rot. The clue is location: sunscald sits on the sun-facing side of exposed clusters and leaves, concentrated on the hot afternoon side of the vine, and it appears in lockstep with a heatwave rather than spreading berry to berry.

Ironically, sunburn is often self-inflicted. Pulling too many leaves to “let the sun in” — especially all at once, right before a hot spell — strips the dappled shade that protected the fruit and leaves it exposed to full afternoon sun. The fixes are gentler canopy management (thin gradually, keep some cover, favour the morning side), steady watering, and in hot climates a reflective kaolin-clay spray or temporary shade cloth during extreme heat.

What to look for

  • Brown, sunken, leathery scald patches on the sun-facing side of exposed berries.
  • Shrivelled, raisined berries on over-exposed clusters after a heatwave.
  • Bleached, tan, papery dead patches on sun-struck leaves.
  • Damage concentrated on the hot afternoon (west/south) side of the vine.

Treatment options

Cultural & prevention

Start here — habits that stop problems before they spread.

  • Keep a light, dappled cover of leaves over the fruit zone rather than fully exposing clusters.
  • Pull leaves gradually and early in the season, and favour the cooler morning (east) side.
  • Keep vines adequately watered through heat; drought-stressed vines scald far more easily.
  • Avoid heavy, sudden canopy thinning right before a forecast heatwave.

Organic / low-toxicity

Gentler sprays and biologicals for active outbreaks.

  • Kaolin-clay particle-film sprays put a reflective coat on fruit and leaves to reduce heat load.
  • Temporary shade cloth over the fruit zone during extreme heat events.

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. Sunburn on Grape — University of Kentucky, Department of Plant Pathology
  2. Sunburn in Grapes: A Review — Frontiers in Plant Science (PMC)
  3. Grape sunburn damage prevention assessed in novel study — Wine Australia
  4. Missing Links in Predicting Berry Sunburn in Future Vineyards — Frontiers in Plant Science (PMC)