# Sunburn & sunscald

- URL: https://backyardgrapes.com/diseases/sunburn/
- Category: Disorder
- Affects: Leaves, Fruit clusters
- Severity: moderate
- Favored by: Heatwaves and intense sun, especially after sudden exposure from leaf removal or over-thinning; reflected heat and water stress make it worse.
- Easily confused with: Botrytis bunch rot (grey mould), Sour rot

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

**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 — Cultural / prevention:**
- 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.

**Treatment — Organic / low-toxicity:**
- 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.

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.

**Image credits:**
- Sunburned green grape berries with brown, sunken patches on the exposed side of a cluster — [Photo: Sandra Julian, American Vineyard Magazine](https://americanvineyardmagazine.com/preventing-sunburn-on-grapes)
- 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](https://www.ipmimages.org/browse/detail.cfm?imgnum=5335093) (CC BY-NC 3.0 US)
- Chardonnay cluster with sunburn scald and raisined berries — [Photo: Agne27, Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Damaged_and_sunburnt_Chardonnay_clusters.JPG) (CC BY-SA 3.0)
- Sunburned Riesling grapes: a cluster with shrivelled, browned berries next to unaffected berries — [Photo: Joanna Gambetta, SevenFifty Daily](https://daily.sevenfifty.com/preventing-grape-sunburn-wine/)

**Sources:**
- [Sunburn on Grape](https://fruitscout.mgcafe.uky.edu/sunburn-grape) — University of Kentucky, Department of Plant Pathology
- [Sunburn in Grapes: A Review](https://pmc.ncbi.nlm.nih.gov/articles/PMC7819898/) — Frontiers in Plant Science (PMC)
- [Grape sunburn damage prevention assessed in novel study](https://www.wineaustralia.com/news/articles/grape-sunburn-damage-prevention-assessed) — Wine Australia
- [Missing Links in Predicting Berry Sunburn in Future Vineyards](https://pmc.ncbi.nlm.nih.gov/articles/PMC8545822/) — Frontiers in Plant Science (PMC)