How to Identify & Prevent Tomato Sunscald
Tomato sunscald is a common problem that occurs when tomato fruits are exposed to intense, direct sunlight, particularly during hot weather. Unlike a disease, sunscald is a form of sun and heat damage that often affects fruits that become exposed after excessive pruning, leaf loss, or extreme weather.
The good news is that tomato sunscald is usually preventable. Understanding what causes it, recognizing the signs early, and taking the right steps to protect exposed fruit can help prevent further damage throughout the growing season.
What Does a Sunscald Tomato Plant Look Like
Tomato sunscald usually develops on the side of the fruit that receives the most direct sunlight. The affected area may:
- Turn pale, white, or gray
- Look bleached
- Become slightly sunken
- Develop dry, leathery skin
- Turn brown or black as tissue deteriorates
Sunscald typically affects only the exposed portion of the fruit rather than spreading across the entire tomato. In severe cases, the damaged tissue may crack or become susceptible to secondary rot.
What Causes Tomato Sunscald
The primary cause of tomato sunscald is intense, direct sunlight combined with high temperatures. Several growing conditions can increase a tomato's exposure to these conditions and make sunscald more likely.
Intense Direct Sunlight
If you live in an area with very strong sunlight and your tomato plants are fully exposed without any shade, the fruit may be more prone to sunscald. Similarly, tomatoes that are suddenly moved from indirect light to intense, direct sunlight may be more vulnerable to developing sunscald even with some leaf cover.
Extreme Heat
High temperatures can increase the risk of sunscald because the surface of an exposed tomato can become considerably hotter than the surrounding air. When extreme heat occurs together with intense sunlight, the exposed fruit tissue is more likely to suffer sunburn.
Underwatering
Underwatering does not directly cause sunscald, but water stress can make the problem worse. When tomato plants do not receive enough water, they may become stressed, wilt, and lose healthy foliage. Reduced foliage can leave developing fruit more exposed to direct sunlight and heat.
Poor Plant Health
A stressed or unhealthy tomato plant may have difficulty maintaining a dense, healthy canopy. Inadequate watering, severe heat stress, pest infestations, diseases, and certain nutrient problems can contribute to leaf damage or loss.
Excessive Pruning
Healthy tomato leaves provide natural shade for developing fruit. Although pruning can improve airflow and help manage plant growth, removing too many healthy leaves can expose tomatoes that were previously protected by the canopy. Heavy pruning during hot, sunny weather can therefore increase the risk of sunscald.
How to Prevent Sunscald on Tomatoes
The best way to prevent tomato sunscald is to maintain enough healthy foliage to provide natural shade while keeping the plant properly watered.
Choose the Right Varieties
Prevention starts with smart plant selection. Look for tomato varieties with a dense, heavy foliage canopy that naturally protects the fruit. Also, choose varieties resistant to common defoliating diseases like Fusarium and Verticillium wilts (often labeled with "V" and "F" on seed packets).
Water Consistently
Consistent watering helps tomato plants maintain healthy foliage and cope with hot weather. Avoid letting the soil become extremely dry before watering, as sudden changes in soil moisture can stress the plant.
Instead, water deeply and regularly, and consider using a drip irrigation system to deliver water directly to the root zone with less evaporation. During hot weather, check the soil moisture more frequently.
Mulch the Plants
Mulching helps conserve soil moisture and moderate fluctuations in soil temperature, which can be especially useful during hot weather. Apply about 2 to 3 inches of organic mulch around the base of the plant, but leave a small gap around the stem to reduce the risk of excessive moisture around the stem.
Provide Shade
During periods of exceptionally hot and sunny weather, temporary shade can reduce the amount of direct sunlight reaching exposed fruit. A 30% to 50% shade cloth can help protect tomatoes from intense solar radiation while still allowing enough light for photosynthesis. Install the shade so that it reduces the strongest afternoon sunlight without completely blocking light throughout the day.
Prune Carefully
Prune selectively and avoid removing large amounts of healthy foliage at once. If possible, do heavier pruning earlier in the season or before periods of extreme heat. During hot weather, focus on removing dead, diseased, or severely damaged leaves rather than healthy foliage that is providing shade.
Keep Plants Healthy
Healthy tomato plants are better able to maintain the foliage needed to protect developing fruit. Provide adequate water and nutrients, and give plants enough space for good air circulation. Regularly inspect plants for pests and diseases, and address problems early to prevent extensive leaf damage and loss of the natural canopy.
Can Plants Recover from Sunscald
Yes, plants can usually recover from sunscald, especially when the damage is limited. However, sunscalded tissue cannot recover or return to its original condition. Once tomato tissue has been damaged, the affected area will remain damaged. The goal is to prevent further injury. If only part of the fruit is affected, the undamaged areas can often continue to develop and ripen normally.
Can You Eat Sunscald Tomatoes
Yes, slightly sunscald tomatoes are generally safe to eat. Sunscald is caused by excessive sunlight and high temperatures, rather than by a disease or toxin. If the tomato is otherwise healthy, simply cut away the damaged area before eating it. However, if the tomato has mold, an unpleasant odor, extensive soft rot, or other signs of decay, it should be discarded.
Conclusion
Tomato sunscald is primarily a sun and heat damage problem, not a disease. It is most likely to occur when intense sunlight reaches exposed fruit, particularly during hot weather or after the plant loses protective foliage.
Keeping healthy leaves around developing tomatoes, maintaining consistent soil moisture, pruning carefully, and providing temporary shade during extreme heat can significantly reduce the risk.
With the right balance of sunlight, water, foliage, and airflow, tomato plants can continue developing healthy fruit even through challenging summer conditions.
