Tomato Sunscald: What To Do About Sunscald On Tomatoes

Tomato Sunscald: What To Do About Sunscald On Tomatoes

By: Nikki Tilley, Author of The Bulb-o-licious Garden

Sunscald commonly affects tomatoes, as well as peppers. It’s generally the result of exposure to sunlight during extreme heat, though may be caused by other factors as well. While this condition is not technically dangerous to plants, it can damage fruits and lead to other issues that could become a problem.

Symptoms for Sunscald in Tomatoes

On tomatoes, sunscald will appear as a yellow or white-spotted area on the side or upper part of the fruit that has been directly exposed to the sun. As the fruit ripens, the affected area may become blistered before it finally turns thin, wrinkly, and paper-like in appearance. At this stage, the fruit becomes more susceptible to secondary fungal problems, like Alternaria.

Causes of Sunscald Tomatoes

To find cause of sunscald in tomato plants, you should look towards one of the following possibilities:

  • Is the fruit exposed to direct sun?
  • Is the weather dry and hot? This is the most likely cause.
  • Have you pruned lately or disturbed the vines while harvesting? The removal of foliage or broken vines can also expose the fruits to sun damage.
  • Have plants recently lost foliage due to pests or disease? This too can lead to tomato sunscald, as the fruits have no cover from the sun’s blaring heat.
  • Finally, when did you last fertilize and with what? A lack of nitrogen once the fruits have set can contribute to this problem as well.

What to Do About Sunscald on Tomatoes

While there is little you can do once you see sunscald on tomatoes, there are things you can do to help prevent this condition. Growing tomato plant varieties that have heavy foliage can help protect the fruits from the sun’s rays, especially during intense heat.

Disease-resistant types can also prevent sunscald by guarding against leaf drop associated with many diseases.

Keeping plants properly spaced can reduce sun exposure and using tomato cages or staking tomato plants will minimize the need for any pruning.

The use of fungicide throughout the season can help control any fungal issues that do pop up, especially those responsible for leaf drop (which leave the fruits exposed).

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Tomato Diseases

Early blight, a fungal disease, is a common problem east of the Mississippi and in the Far West. The first signs of trouble appear on the lower leaves as small brown spots with concentric rings in their centers and yellow margins. Affected leaves eventually turn yellow and fall from the plant. Fruits may also be affected. Warm, humid weather favors the spread of this disease.

To help keep early blight in check, clean up all tomato plant remains at the end of the season -- disease-causing spores can survive over the winter on plant debris. Mulch plants to reduce splashing spore-carrying soil onto leaves during rains, avoid wetting the foliage when you water, and make sure there's good air circulation around plants by not crowding them.

Some chemical fungicide sprays can control early blight if applied regularly when weather conditions are favorable for the spread of the disease. Check with your local county Extension agent to find out what fungicides are recommended in your state. Be sure you read the label and follow all the directions carefully when using any pesticide.

Late blight is another fungal disease that affects tomatoes in the same geographical areas as early blight. Leaves develop bluish gray spots, then turn brown and drop. Fruits develop dark brown, corky spots. Wet weather with warm days and cool nights sets the stage for this disease, which also infects potatoes.

To control late blight, avoid wetting the foliage when you water, use an approved fungicide regularly and clean up tomato plant debris in the garden at the end of the season.

Leaf spot can be caused by several different kinds of fungi. It's often a problem in the southeastern states and some northern areas that have warm, moist weather. Septoria leaf spot is common in the Northeast, mid-Atlantic and Central states gray leaf spot is common in the Southeast. Septoria begins with many small brown spots with black specks in their centers older leaves are affected first. Eventually infected leaves turn yellow and drop. Gray leaf spot is similar, except that the spots have gray centers.

The fungi that cause these diseases live on old tomato plant debris in the soil and nearby perennial weeds. Rotating crops from one spot to another in the garden each year is one way to keep this disease in check. Clean up the garden well at the end of the season, avoid overhead watering and apply an approved fungicide regularly.

Notes on Disease Prevention

Rotate your crop of tomatoes each year to avoid soil-borne diseases. Some serious diseases can live in the soil for several years. Try to wait three years before planting tomatoes where they grew before. Also, avoid planting where potatoes, eggplants or peppers grew the previous season, because some diseases attack all these vegetables and live in the soil from year to year.

Plant resistant varieties. Many tomato varieties are resistant to Verticillium and Fusarium wilts, for instance. Most seed companies list resistance to these diseases by putting F (Fusarium) or V (Verticillium) after the variety name. N stands for resistance to nematodes, the tiny worms that plague many southern gardens, causing stunting of the plants and poor crops.

Don't smoke in the garden -- you can infect plants with tobacco mosaic virus, a disease that can really cut down on the harvest. Look for a T after the variety name for resistance to this disease. If you smoke, wash your hands with soap and water before handling tomato plants.

Clean up the garden well at the end of the season. Many disease-causing organisms spend the winter in plant debris in the soil. Destroy any obviously infected plant material rather than composting it.

Help is available if you need it. Your local county extension service can help you identify diseases and recommend remedies. Many offices publish pamphlets with pictures and descriptions of tomato plant problems you may encounter in your part of the country.

Fix tomato woes like blossom drop, leaf roll, sunscald: Gardening basics

Closeup of the "legend" tomato developed at the OSU vegetable farm near Corvallis. Excessive nitrogen and overhead watering can cause problems with tomatoes.

Are your neighbors' tomatoes plump and juicy and yours struggling? Brooke Edmunds, a horticulturist with Oregon State University Extension Service, troubleshoots common problems:

Tomatoes can suffer from a number of problems, including leaf roll, sunscald and blossom drop

Blossom drop – Usually caused by dry soil and dry winds, but also may be the result of a sudden cold spell, heavy rain or too much nitrogen. Typically, not all blossoms will fall off, so be patient and wait for the next set of flowers.

Blossom-end rot­ ­­– If the end of the fruit farthest away from the stem turns brown or black, it's a condition caused by irregular watering practices and calcium deficiency and is most common in western Oregon. Water deeply and regularly. Add lime to the soil in the fall to increase the calcium level for next year's crop.

Early and late blight – These are fungal diseases, characterized by spots on lower leaves and stems that appear water-soaked. Avoid overhead watering, and remove diseased leaves.

Growth cracks

Extremely fast fruit growth can cause growth cracks. This may be caused by periods of abundant rain and high temperatures, or can happen when it rains or you water plants after a period of drought.

Cracks may radiate from the stem end of the fruit or may encircle the fruit. Cracks are often invaded by secondary fungi and bacteria that further rot the fruit.

Maintaining even moisture by watering regularly and mulching the soil around the tomato plant can help reduce growth cracks.

Varieties differ in susceptibility to cracking, and variety descriptions may be helpful in choosing a plant less likely to crack.

Pros and Cons of Pruning Tomato Plants

Below, I have included a table that summarizes the pros and cons of pruning tomato suckers. More detail on the pros and cons follows the table.

larger fruitless fruit
easier to
more work
to prune
less disease
from soil
more disease
from cuts
on plants
more plants
if you root
sunscald on
plants with
fewer leaves

Pros of Pruning Tomato Plants

There are several advantages to pruning the suckers on tomato plants:

  • Larger fruit – with fewer suckers, there will be fewer flowers, and thus fewer tomato fruits on the vine. The plant can then focus its energy on growing fewer but larger tomatoes.
  • More manageable – with fewer suckers, it is easier to tie tomato plants to a support. It is also easier to harvest the fruit when it appears.
  • Less disease from soil – according to the University of New Hampshire Extension, keeping plants off the ground reduces fungal diseases, such as early blight. Pruning off the lower suckers keeps the plant from touching the soil, where diseases may lurk.
  • More plants – if you wish, you can try to root any tomato suckers that you cut off of a plant. If you are successful, you will get even more tomato plants, although they will have a much later start than your original plant.

Cons of Pruning Tomato Plants

For all of the advantages, there are also some drawbacks to pruning the suckers on tomato plants:

  • Less fruit – if you prefer lots of fruit, pruning is not for you. You will get fewer flowers and fruit from both indeterminate and determinate tomato varieties if you prune them. You can learn about how to get more fruit from tomato plants in my article here.
  • More work – it will take more work up front to prune the suckers from your tomato plants.
  • Infection – when you cut or break off part of a plant, there is a risk of infection by bacteria or viruses through the opening. You need to weigh this risk against the reduced risk of disease from the soil getting onto low-hanging branches.
  • Sunscald – if you prune off too many suckers, the tomato plant will have fewer branches and leaves as it grows. This reduced canopy will offer less protection against sunlight. If there is not enough protection for fruit, they may get sunscald spots, which also invites mold and other problems.

Sunscald: Too Much of a Good Thing

pecies can get too much of a good thing. When foliage or fruit is exposed to excessive sunlight, plant tissue can get a bit of sunburn, generally referred to as sunscald. Sunscald is often exacerbated by high temperature and drought.

Sunscald symptoms will appear as yellow or white lesions on foliage and/or fruits. The lesions eventually may turn brown and/or shrivel. Foliage that is commonly affected includes impatiens, hosta, rhododendron, garden beans, peas, peppers and tomatoes.

Fruits that are frequently victim of sunscald include tomatoes, peppers, strawberries, raspberries, blackberries, grapes and apples. In many cases disease and insect damage to the foliage, or excessive pruning, results in the fruits becoming over exposed to sunlight. Once the fruit is damaged, other soft rots may invade the fruit to cause further damage.

Encouraging healthy foliage by proper positioning in the garden, appropriate fertilization, pruning and pest control can help prevent sunscald on garden plants. Using tents or screens to provide light shade in late afternoon may also help. Moving susceptible perennials and shrubs to more-protected locations, particularly away from the afternoon sun, may be warranted.

Young trees, particularly thin-barked species such as apples, crabapples, cherries, maple, tuliptree, ash and poplar, may also experience sunscald. Prevent sunscald to young trees by wrapping the trunks with paper or plastic tree wrap products that are specifically designed for this purpose. These wraps should be applied in late fall or early winter and removed by early spring to avoid overheating the young bark during the growing season. After two or three growing seasons, the bark should no longer need wrapping.

Fusarium and Verticillium Wilt

Fusarium and Verticillium wilt are caused by fungi in the soil that enters your tomato plants through the tender, young roots. The fungi then plugs the vessels that gets water from the roots to the stems. As you can imagine, your plants will begin to decay due to lack of water flow. On sunny days your plants will appear wilted, then appear to recover during the night (wilting may first appear in the lower or upper leaves of the plant, causing discoloration). Eventually leaves will die backward from the leaf tips as the wilting spreads throughout the entire tomato plant. Fusarium wilt is the most common tomato plant disease in regions with warm weather regions as well as in cooler regions during the periods of warmest weather.

To avoid these tomato plant wilt diseases, make a point to plant tomatoes bred for disease resistance (Heirloom tomato varieties in particular not bred to withstand these types of diseases are particularly susceptible to tomato wilt). Look for plants labeled with an "F," "FF," or "FFF" (for Fusarium variations), or with a "V" (for Verticillium). Be sure not to overwater your tomato plants--a wilted plant does not mean it needs more water, so check the soil. If it's dry, then go ahead and water.

If your tomato plants are affected by any of these wilt diseases, extract and destroy them. Do NOT place them in your compost pile. Do not plant tomatoes, peppers, potatoes, or eggplants in affected soil for four to six years because of residual fungus that remains in the soil (corn and beans won't be affected). Keep affected soil well weeded as their roots continue feeding on the fungi.

Watch the video: Tomato Leaves Turning White Tomato Sunscald