Weather Forecast


Troubleshooting your tomatoes

Fungicides for tomato disease control are most effective if applied as preventatives before symptoms appear. Dave Wallis / The Forum

Gardeners are an optimistic bunch who usually don’t go picking fights. But when it comes to protecting our tomatoes, most of us will gladly join the battle.

It sounds pessimistic, but expecting tomato trouble is the best defense. We don’t think about tomato problems until fruits are rotten and leaves are lemon-yellow, curled and speckled. Then we question the cause and ponder a remedy.

Unfortunately it is often too late because most remedies must be applied as prevention before problems becomes visible. Let’s prepare a plan of prevention while there’s still time for defense.

Blossom end rot is very common and sneaky. On the long-awaited day of harvest, you grasp the red fruit, gently pull it from the vine, turn it over to admire, and you discover the lower half is shrunken, leathery-brown or rotten black.

Plant disease literature is somewhat upbeat about blossom end rot because they call it physiological. Somehow that never cheers me up, and physiological sounds like a condition for which you need to visit a clinic.

Physiological means it is not caused by disease organisms but by the conditions or environment in which the tomato is growing. Technically, it is caused by calcium deficiency within the plant.

Calcium is plentiful in our area soil, but plants are sometimes unable to absorb and use it. Blossom end rot usually happens to the first fruits set when soil temperatures are cool. Plants can’t utilize calcium until soil temperatures warm, and fruits formed later are often fine.

We can help tomato plants utilize soil calcium. Calcium uptake is associated with water uptake, and anything that interferes with water uptake will affect calcium uptake. Maintain a uniform moisture supply around tomatoes to avoid wet/dry swings. Mulches help greatly. Avoid cultivating within 12 inches of tomato plant stems, because it tears calcium-carrying roots.

If you fertilize tomatoes, examine the label for nitrate forms of nitrogen instead of ammonia types that inhibit calcium uptake. Avoid over-fertilizing, which can cause an overabundance of leafy growth.

Calcium sprays are marketed for application to leaves and fruits but research has not proven their effectiveness. Epsom salts are often touted as a home remedy, but Cornell University disagrees because the high magnesium content of the salts can actually make the condition worse.

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

Leaf roll is another physiological disorder in which tomato leaf edges roll upward until they almost touch becoming tube-like. Lower 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 overly 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 paper-like texture.

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

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.

Herbicide injury from 2,4-D farm and lawn spray easily affects 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 stems split and distort. Whether plants recover depends on severity of spray drift.

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, leaf spots 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 preventives before symptoms occur, or at their earliest signs. Garden supply companies have different product names, but the most common garden disease preventives contain chlorothalonil as indicated on the label.

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.

Kinzler, a lifelong gardener, worked as a North Dakota State University Extension horticulturist and owned Kinzler’s Greenhouse in Fargo. Readers can reach him at