Tomato Sunscald: Cause, Symptoms and Preventive Measures
Tomato sunscald is not a disease and can, therefore, be easily prevented. It develops on the face of the fruit that is exposed to the sun. First seen as light patches on the unripe or ripening fruit, it doesn't just affect tomatoes but is a common sight on peppers, squash, watermelon, etc. It always occurs when the fruit is exposed to direct sunlight in already hot weather conditions.
What Does Tomato Sunscald Look Like?
The image above illustrates what an affected tomato looks like during the mid-stages of being damaged. The progress of tomato sunscald with continued exposure to direct sunlight is as follows:
- Light patches of white on unripe tomatoes or yellowish patches on ripening fruit.
- The white or yellow patches begin to blister.
- The shape of the tomato is lost around the affected area as it flattens (some refer to it as being sunken) and the layer becomes thin and papery. It may seem greyish-white at this stage as seen in the image above.
- If the fruit is still growing, this region of the skin does not expand with the growing fruit underneath and it can rupture. To understand why this happens, read my article on why do tomatoes split, it is essentially the same principle, albeit a different cause.
- Black mold forms on the ruptured area as the fruit begins to rot around the affected region before spreading.
Causes of Sunscald Tomatoes
There is just one ultimate cause and that is direct exposure to sunlight in hot weather conditions. However, there are common mistakes that gardeners make which ends up exposing their tomatoes to the scorching sun. I, therefore, list these common mistakes as causes.
- Failure to protect exposed tomatoes either by repositioning them to be under existing foliage or by adding shade.
- Disturbance of the vine while harvesting, especially if you've got indeterminate varieties.
- Unplanned pruning that makes it nearly impossible to protect fruit using existing foliage.
Preventing Tomato Sunsclad
In my opinion, as seen in the introduction, this issue is easily prevented when the following preventive measures are followed:
- Plant smart - If you live in a region where the mercury soars around harvest time it would be wise to plant varieties that are heat resistant. Tomato Dirt has a list of heat-tolerant varieties. Staying away from varieties with sparse foliage is generally a good idea for high heat environments.
- Maintain and encourage foliage growth - Nitrogen promotes the growth of foliage. You should, therefore, fertilize with the right nutrients necessary for a particular stage of growth.
- Water sufficiently and correctly - Water sufficiently so that the plant is never stressed due to too much or too little water, allowing it to grow healthy. Do not water on the leaves in the evenings as dampness over prolonged periods without the sun to dry up the leaves helps pathogens infect the plant. Read my related article for further guidance on the best watering techniques.
- Be a step ahead of diseases - Most tomato plant diseases affect foliage and when they do it is best that you prune the leaf or the affected region to prevent the spread of the disease. Pruning during fruition, however, can leave sheltered tomatoes suddenly exposed.
- Mulch - An inch or more of mulch is always recommended. Mulch is mainly associated with retaining moisture and for its slow release of nutrients into the soil. What is often overseen is the fact that it prevents soil from splashing onto the plant as you water. Many of the pathogens that end up destroying the foliage get to your plant from splashing up onto lower leaves.
- Pruning - Don't over prune, this goes without saying. If you are pruning to shed weight, you could support your plants externally using stakes, a cage, trellis, or any other innovative method that would serve the purpose.
- Shade exposed tomatoes - There are going to be instances where tomatoes are left exposed even if you follow the points above. If you have got exposed fruit and expect high temperatures use a , wet straw, or a shade screen. Keep in mind that your tomato plant is going to need 6 - 8 hours of sunlight to produce energy for the sustenance of fruit growth. Local shading is the best option when possible. Read my related article to understand shade clothhow much sun tomatoes need.
Controlling the Spread of Sunscald
Unfortunately once affected, there's no cure to sunscald on your tomatoes. The good news is that you can slow or stop its progress.
On fruit that is still growing and shows no sign of ripening, the best that you can do is slow its progress by shading the fruit.
If the fruit is already beginning to change color and showing signs of ripening harvest the fruit and let it continue to ripen indoors. This is recommended for healthy fruit too as it prevents many other problems, splitting tomatoes for instance.
Can Sunscald Tomatoes Be Eaten?
Yes, there's no harm in eating affected fruit provided that it hasn't begun to mold. All you need to do is cut off the affected region and use the fruit as you would any other.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.