Sunscald on tomatoes can wipe out a harvest fast. Ninety percent of a Caspian Pink crop, gone in a single brutal stretch. That was one Southern California grower’s real tally.
Thinner skinned, slow ripening pink varieties took the worst of the damage.
That same gardener noticed something else worth knowing. Juliette and Cherokee Green held up far better, and caged plants fared better than sprawling ones. More leaves packed into a smaller space seemed to matter.
This site’s fruit problems guide already covers the basics of sunscald. This guide goes deeper. It covers the actual mechanism, real variety differences, and exactly when a scalded tomato is still worth eating.
The short version
Sunscald happens when a tomato loses its leaf cover and gets hit with direct sun. Research traces the real damage to a combination of heat and light working together, not heat alone.
Thick skinned, small fruited varieties tend to resist it better than large, thin skinned ones. Sudden defoliation from storms, disease, or heavy pruning causes the worst cases.
Shading exposed fruit and keeping the canopy full are the main defenses. Minor scald can usually be trimmed and eaten. Heavy scald with rot should be tossed.
What is actually happening inside the fruit
Sunscald looks like sunburn, and most guides leave it there. The real story is more specific.
A 1974 study in Scientia Horticulturae tracked exactly what triggers the damage. Rabinowitch, Kedar, and Budowski ran the research.
Fruit surface temperatures needed to reach somewhere between thirty nine and forty one degrees Celsius before injury began. That is about one hundred two to one hundred six degrees Fahrenheit. Damage peaked after eighteen hours at forty five degrees Celsius.
A longer twenty eight hours at a cooler forty one degrees caused similar damage. Heat alone was not the whole story, though. Light in the visible spectrum turned out to be essential too.
Fruit exposed to both heat and light together developed scald one hundred percent of the time. Fruit that got the same heat with light withheld afterward only scalded sixty eight percent of the time. The light itself was doing real damage, not just the heat.
The researchers described this as an abnormal photodynamic reaction. Heat appears to disrupt how the fruit’s own chlorophyll handles light energy. That turns a normally harmless process into one that burns tissue from the inside.
That is a very different picture than simple sunburn. Under natural outdoor conditions, the same research team measured roughly thirty five percent injury. That figure came after just six hours of peak sun and heat.
Sudden, unbroken exposure during the hottest part of the day is genuinely worse than the same total sun spread across a full day.
Green fruit and ripe fruit scald differently
Washington State University’s Hortsense fact sheet draws a real distinction most gardeners never hear. Green fruit develops a yellowish, light brown, or white leathery patch that often turns wrinkled or blistered.
Ripe fruit reacts differently. The damage there shows up as a flattened, grayish white patch with a papery texture instead.
Both stages can still develop secondary rot in the damaged tissue. University of Illinois Extension names the usual culprits directly, fungi in the Alternaria, Brachysporium, and Cladosporium groups. They move into scalded tissue once its natural defenses are gone.
Which tomatoes are more at risk
Forum experience and university guidance line up closely here. Kansas State University Extension notes that pear shaped and processing type tomatoes resist sunscald better than large slicing varieties.
That tracks with what californian found firsthand. Juliette, a small grape type, and Cherokee Green held up well. Caspian Pink, a large pink heirloom that ripens slowly, did not.
University of Illinois Extension adds that varieties with a naturally dense, slow spreading canopy protect their own fruit better. Peppers get a similar built in advantage when their fruit hangs downward. Tomato fruit clusters do not hang the same way, though.
Caging versus staking matters too, based on californian’s observation. A cage packs more leaf area into a tighter space around the fruit. A sprawling, loosely staked plant leaves more open gaps for direct sun to reach through.
Why the leaf cover disappears in the first place
Every source agrees on the trigger. Sunscald needs a canopy that used to shade the fruit and suddenly stopped.
University of Maryland Extension points to early blight as a common cause. That disease strips lower and inner leaves fast once it takes hold.
Heavy or poorly timed pruning does the same thing on purpose. Storm damage, hail, and wind can strip leaves in a single afternoon too, according to Kansas State University Extension.
Any of those events leaves fruit that spent weeks developing in shade suddenly exposed to full sun with no transition. That abrupt switch is exactly the condition the 1974 research found most damaging.
Preventing it
Keeping the canopy intact matters more than any other single step. This site’s pruning guide covers how to remove suckers and lower leaves without stripping the protective cover fruit actually needs.
Disease control protects the canopy from the inside. University of Illinois Extension recommends a copper based fungicide or a chlorothalonil based fungicide for orchards and market gardens fighting early blight. The schedule there starts once fruit clusters form and repeats every five to ten days.
A home garden rarely needs that full a schedule. The same active ingredient categories still work at a lighter, less frequent rate.
Physical shading covers fruit that is already exposed. Kansas State University Extension suggests cheesecloth draped over vulnerable clusters. Texas A&M AgriLife Extension recommends straw or lightweight row cover fabric for the same purpose on a small scale.
Purdue University Extension takes a slightly different angle. It recommends a tent or screen positioned to block only the harshest late afternoon sun.
None of these sources gave a specific shade cloth density. Match the material to how much filtering your hottest afternoon hours actually need.
Washington State University’s Hortsense fact sheet is direct about one thing. No chemical product treats sunscald once it happens. Prevention through canopy and shade is the only real lever.
Is it safe to eat?
Usually, yes. Kansas State University Extension states plainly that fruit with minor scald is fine to eat once the damaged patch is cut away.
Heavily scalded fruit is a different case. Extensive damage, especially with visible mold or a soft, collapsed texture, means rot has already moved in and the fruit should be discarded.
Kansas State University Extension adds one more practical tip. Removing badly scalded fruit promptly can encourage the plant to set more fruit. The plant stops wasting energy on something already lost.
Frequently asked questions
What actually causes sunscald on tomatoes?
Fruit that loses its leaf cover gets hit with direct heat and sunlight at the same time. Research shows both heat and visible light are needed together to cause the damage. Heat alone causes far less injury than the combination.
Do all tomato varieties get sunscald equally?
No. Pear shaped and processing type tomatoes tend to resist it better than large, slow ripening slicing varieties. Thinner skinned heirlooms and big pink varieties tend to suffer the worst damage.
Can I still eat a tomato with sunscald?
Yes, if the damage is minor. Cut away the scalded patch and eat the rest. Heavily damaged fruit with mold or a soft, collapsed texture should be thrown out instead.
How do I stop sunscald before it starts?
Keep the plant’s leaf canopy full through careful pruning and early disease control. Shade exposed fruit directly with cheesecloth, row cover fabric, or a simple screen. Focus that shade on the hottest part of the afternoon.
Is there a spray that treats sunscald?
No product treats the damage once it happens. A preventive fungicide can still help, though. It protects the leaf canopy from the diseases that cause most defoliation behind sunscald.
The bottom line: sunscald on tomatoes comes from a real, researched combination of heat and light hitting fruit that lost its shade too suddenly. Thick skinned, small fruited varieties handle it better than large heirlooms, and a full leaf canopy is still the best defense. Minor scald is safe to trim and eat, and heavy scald belongs in the compost. For the wider lineup of fruit disorders this fits into, see our tomato fruit problems guide. For pruning without stripping the leaf cover that prevents this, see our how to prune tomatoes guide. For the diseases that often cause the defoliation behind it, see our tomato diseases guide.
SOURCES
Rabinowitch, Kedar, and Budowski: Induction of Sunscald Damage in Tomatoes Under Natural and Controlled Conditions. Scientia Horticulturae, 1974. https://www.sciencedirect.com/science/article/abs/pii/0304423874900351
Washington State University, Hortsense: Tomato, Sunscald. https://hortsense.cahnrs.wsu.edu/fact-sheet/tomato-sunscald/
University of Illinois Extension, Vegetable Diseases: Sunscald of Pepper and Tomato. http://ipm.illinois.edu/diseases/series900/rpd939/rpd939.html
Kansas State University, Horticulture Resource Center: Tomato Sunscalded Fruit. https://hnr.k-state.edu/extension/horticulture-resource-center/common-pest-problems/documents/Tomato%20Sunscalded%20Fruit.pdf
Texas A&M AgriLife Extension, Vegetable Problem Solver: Sun Scald. https://aggie-horticulture.tamu.edu/vegetable/problem-solvers/tomato-problem-solver/green-fruit/sun-scald/
University of Maryland Extension: Sunscald on Vegetables. https://extension.umd.edu/resource/sunscald-vegetables
Purdue University, Yard and Garden News: Sunscald, Too Much of a Good Thing. https://www.purdue.edu/hla/sites/yardandgarden/sunscald-too-much-of-a-good-thing/