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Expecting trouble is the best way to keep tomatoes healthy

"Growing Together" columnist Don Kinzler says most remedies for tomato troubles are best as preventative steps rather than trying to fix current problems.

Many tomato problems can be prevented or stopped before it's too late.
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FARGO — It sounds pessimistic, but expecting trouble is the best way to keep tomatoes healthy. If we take no action until we observe rotten fruit and yellow, speckled leaves, the window of prevention is gone.

Most remedies for tomato troubles are best applied as prevention before problems becomes visible. The following are the most common problems with recommended solutions.

Blossom end rot

Blossom end rot is very common and results in the tomato fruit’s lower portion turning shrunken, leathery-brown or rotten-black. The disorder is physiological, which means it isn’t caused by disease organisms, but by the conditions or environment in which the tomato is growing.

Technically, the disorder is caused by calcium deficiency within the plant. Calcium is plentiful in most area soils, but situations cause plants to be unable to absorb the available calcium.

We can help tomato plants utilize soil calcium by maintaining a uniform moisture supply around tomatoes to avoid swings between wet and dry. Mulches greatly reduce blossom end rot. Avoid cultivating within 12 inches of tomato plant stems, because it tears calcium-carrying roots.


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Overfertilizing tomatoes can cause an overabundance of leafy growth and increase blossom end rot, so fertilize modestly, if at all. Calcium sprays are marketed for application to leaves and fruits but research is inconclusive, and timing of application is critical.

Epsom salts are often touted as a home remedy, but nearly all research universities disagree, because the high magnesium content of the salts can make the condition worse.

Some tomato varieties are more resistant to blossom end rot, including Early Girl, Mountain Spring and Celebrity.

Tomato disease
Tomato disease problems are among those most encountered by gardeners.
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Leaf roll

Leaf roll is another physiological disorder in which tomato leaf edges roll upward until they almost touch, becoming tubelike. The lowest plant leaves are usually affected first, and once they roll up, they often do not unroll, even if conditions improve.

It’s worse in hot, dry weather but can occur during periods of active plant growth and high production even if moisture is plentiful. Research shows it does not affect overall growth and fruit production, and there is no known prevention.


Sunscald occurs when fruits are exposed to sun because leaf cover has decreased from insects or leaf diseases. Exposed fruit portions become pale-yellow to white and often have a paperlike texture.

Sunscald is best prevented by maintaining a healthy plant having plentiful leaf cover.


Growth cracks

Growth cracks encircle the fruit, or radiate from the stem end. Not a disease, they’re caused by a rapid surge in fruit growth triggered by a sudden abundance of moisture or heat. Mulching around plants and providing uniform moisture reduces cracking. Some varieties are more susceptible. Plant tags often indicate resistance to cracking.

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Herbicide injury

Herbicide injury from agricultural or lawn weed killers is a common problem affecting tomato plants, which are highly sensitive. Older leaves cup downward with prominent light green veins. Young leaves do not fully enlarge, but become elongated, narrow, leathery and twisted, and stems split and distort. Whether plants recover depends on the severity of spray drift. Fruits from plants affected by herbicides are generally considered unfit for consumption.

Heirloom tomatoes
Blights, sunscald, end rot and more can all affect tomatoes.
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Blights are worrisome because they’re caused and spread by microscopic living disease organisms. Early blight, late blight, septoria spots, verticillium and fusarium wilts are all caused by fungi with symptoms of yellowing leaves, brown circular leaf and fruit lesions, leafspots and plant decline. Control for all is similar.

Some varieties are more disease-resistant as indicated on plant tags by abbreviations like V, F and N resistant.

Fungal diseases easily start in warm, humid, rainy weather. Organisms need moisture to establish. Water plants in the morning so foliage dries before nighttime, and water only the soil rather than overhead sprinkling which splashes organisms from leaf to leaf.

Fungicide sprays can be very effective if applied as preventatives before symptoms occur, or at the earliest signs. A variety of vegetable disease preventers can be found at garden centers, and most contain chlorothalonil or copper as the active ingredients.


Remember to remove and discard tomato plants each fall, because disease organisms live over winter in the soil on leaves and stems. Rotate plants to a different garden area if possible.

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.
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