Tomato Sunscald: When Tomatoes Get Too Much Sun
Do your tomatoes look dry and cracked, or even a little burned? It's quite possible your tomatoes have something called sunscald. Luckily, this is a common ailment, and can be both prevented and remedied. In this article, gardening expert Logan Hailey examines why tomato sunscald happens, and how to treat it.
Tomatoes are one of the most sun-loving crops you can grow, but they can still get sunburnt just like people. Sunscald is a physiological condition that causes tomatoes (and their pepper cousins) to turn pale white or blotchy yellow due to intense heat and sunlight. This can happen to the fruits or the leaves of your tomato plant.
But once it happens, what should you do? And better yet, can sunscald be prevented? As with most tomato problems, prevention is actually the best first step. Sunscald really can’t be treated, but since it’s not an official “disease” it won’t necessarily affect all tomato fruits.
Are you ready to learn a little bit more? Let’s dig into everything you need to know about tomato sunscald, including causes, and prevention!
What is Sunscald?
Tomato sunscald is a condition where the fruits turn white or pale due to overexposure to direct sunlight. It can also happen to peppers, eggplants and other garden veggies.
Sunscald can be caused by a range of plant problems that cause the plant to defoliate or lose significant quantities of leaves. This results in fruits that are exposed to intense sunshine rather than being naturally protected beneath the foliage.
The major symptoms of sunscald include:
- Whitish or pale gray blotches on unripe or ripening fruit.
- Large pale regions on the sun-exposed part of a tomato fruit.
- The blotches turn into blisters.
- Sunken areas form beneath the sunburnt region.
- The fruit around the sunken spot keeps growing, causing splitting.
- Black mold or rot developing beneath the sunscald parts.
- Paper-like pale skin.
While sunscald can often lead to other fruit diseases, you can differentiate it by noticing exactly where the blotches are coming from:
- If it starts where the sun enters the garden and hits the tomato, it’s likely sunscald.
- If the spots are blackened or located on the bottom of the fruit, it’s probably blossom end rot.
- If the areas appear white or fluffy, it’s likely due to powdery mildew.
While these are just a few tomato diseases that look similar to sunscald, there are plenty more to consider before officially diagnosing sunscald.
Sunscald happens when developing fruits are exposed to too much direct sunlight. Sunscald is not necessarily a plant disease, but rather a physiological condition. Anything that causes defoliation or a lack of foliage cover can cause sunscald, including the following.
Blights, mildews, and viruses can aggressively defoliate a tomato plant, causing large portions of the leaves to wither and die. This means there isn’t enough of a canopy to shade and protect developing fruits, leading to sunscald.
If you remove too many leaves from your tomato plant, the fruits can become over-exposed to sunlight. This is the most common cause of sunscald.
When tomato plants are extremely stressed out, they don’t produce the lush healthy leaves needed to support their fruits. When a plant feels like it’s nearing the end of its life, it will sometimes “stress-flower” and grow fruits as a last-ditch effort to reproduce. The result is sunscalded fruit dang.
Although tomatoes are some of the most heat-loving plants, sweltering summer conditions can cause severe stress.
Although sunscald is unsightly, it doesn’t actually affect the edibility of the fruit. As long as there are no secondary infections of black mold or rot on the tomato, you can simply cut off the sunburnt part of the skin and eat the rest of the fruit.
How Do You Treat Sunscald?
Unfortunately, once sunscald takes hold of tomato there is nothing you can do to reverse the condition. The fruit has already been damaged.
However, since this is not a disease or pest, you can easily prevent it from happening to other developing fruits by simply removing the damaged fruit and using shade cloth tunnels to protect the remaining fruits as they ripen. You can seven use a tomato tube cover or a mesh cloche around individual plants.
7 Ways to Prevent Sunscald
If you want blister-free, bright red (or purple or orange) tomatoes, your best option is to take these simple steps to prevent sunscald. It’s not difficult to prevent, but it may require a bit of planning and forethought in your garden.
Keep Fruit Shaded
Contrary to popular belief, tomatoes do not actually require light to ripen. In actuality, exposure to direct light inhibits synthesis of the skin pigments needed for proper ripening, which can lead to the appearance of sunscald.
The key to preventing sunburnt tomatoes is simple: maintain enough healthy foliage that the tomato fruits are protected from the harsh sunlight. Think of leaves as the plant’s natural sunscreen for its delicate fruits. This canopy layer will provide partial to full shade.
Plenty of water, fertility, and sunshine (for the leaves) are essential for healthy lush plant growth. Then, you can use the following preventative methods to maintain that protective leaf layer.
Pruning is crucial for high-yielding plants because it encourages the plant to channel its energy toward fruit production. However, some growers can get overzealous and accidentally remove too much plant foliage. Pruning should start right when tomatoes get planted. But when you prune too many leaves, the fruit are left naked and vulnerable to sunscald.
Like all plants, tomatoes need their leaves to photosynthesize and produce the energy they need for fruiting. If you remove too many leaves, the plant may get stressed out because it cannot support its basic nutritional needs. This leads to less fruit and more susceptibility to disease problems.
Remember that pruning is a great practice for maximizing your yields and preventing diseases. You just don’t want to overdo it! I like to keep at least 1-2 leaves above every flower cluster to provide protection for developing fruit.
Avoid Overhead Irrigation
Tomatoes should be irrigated from the base whenever possible. Overhead sprinklers can lead to water settling on the skin of the fruits, which magnifies more sunlight towards them.
The droplets of moisture hanging out on the plant make intense sunshine even worse. Moreover, overhead irrigation can also lead to disease issues that further defoliate the plant and harm fruit quality.
The best irrigation options are soaker hoses or drip lines along the base of your tomato plants. This keeps the foliage and fruit as dry as possible.
An inch or two of mulch around the base of tomato plants works wonders for preventing water setting on low-hanging fruits and leaves. This is especially useful in rainy climates where heavy rains can lead to droplets splashing from the soil up onto the lower portions of the plants.
Straw, chipped leaves, or landscape fabric are great options for preventing soil-borne diseases while simultaneously suppressing weeds and conserving soil moisture.
Actively Prevent Diseases
Tomato diseases indirectly cause sunscald because they weaken the plant and reduce the amount of leaf coverage. If leaves are yellowing, withering, and falling off, your tomato fruits will be left unprotected from the sun’s harsh rays.
There are a few things you can do to help prevent most diseases, namely the following:
Tomato Disease Prevention Tips
- Maintain proper air flow between plants with pruning (but not over-pruning)
- Choose drip irrigation, soaker hoses, or water from the base of plants
- Use neem oil or compost tea to prevent pathogens
- Avoid overwatering or drought conditions to keep your plants strong
- Remove any leaves that look infected or diseased
- Remove and destroy old plants after every season
Grow Heat Tolerant and Disease Resistant Varieties
Plant breeders have developed some impressive tomato seeds that are resistant to diseases like verticillium wilt, fusarium wilt, late blight, and more.
These tomatoes have resilience to pathogens built into their genetics, making them less susceptible to defoliating diseases that could lead to sunscald. Look for disease resistance codes like F, LB, V, TSWV, EB, and FW in seed catalogs. We love ‘Early Girl’, ‘Sungold’, and ‘Big Beef’.
In areas with extreme summer sun, you can also opt for heat-tolerant tomatoes like ‘Grand Marshall’, ‘Estiva’, ‘Florida 91’, and ‘Heatmaster Hybrid’. These cultivars can withstand intense temperatures and have been bred to maintain plenty of foliage to protect the developing fruits.
If you repeatedly have issues with sunscald or other fruit problems in the late stages of tomato ripening, consider harvesting a little sooner during the “breaker stage”.
This is the point where they just begin to show signs of turning from green to ripe. If you cut them off the vine, you can eliminate a lot of diseases, pest, blemishing, and sunburning risks that may come in those final stages of ripening.
Then, ripen the tomatoes indoors in paper bags or near a banana. The flavor should be just as delicious and you can preserve the quality of your precious tomatoes that you worked so hard to grow.
Tomato sunscald is an easily preventable condition caused by a lack of leafy canopy over the fruits. Tomato plants naturally want to protect their flowers and fruits from intense direct sunlight by growing layers of leafy foliage above them. If you over-prune, overhead irrigate, or face plant disease, your tomato plants may lose the lush canopy they need to shield susceptible fruits from the summer sun.
While sunscald is preventable, there is nothing you can do once it starts bleaching your tomatoes. The best option is to harvest early, cut off the sunscalded parts, and use shade cloth to protect the remaining ripening fruits on the plant.