Troubleshooting Tomatoes

Boulder County Home & Garden Magazine, Online Feature, Spring 2011

From mushy fruit to yellowed leaves, tomatoes can get sick from viruses, bugs, blight and more. If your plants get problems this guide can help you deal with the culprits.

By Carol O’Meara

Tomatoes can suffer everything from early blight to bacterial speck. If your tomatoes are looking peaked, check their symptoms against this list of possible culprits and cures.

Symptom: Leaves chewed to a nub, large pellets littering the area below the plant.
Culprit: Tomato and tobacco hornworms are large, green caterpillars with white stripes and a soft, flexible horn on the hind end. Like hungry teenagers, they quickly strip plants of leaves and damage fruit.
Cure: Hornworms are easy to control. Courageous gardeners pick them off by hand or you can apply Bacillus thuringiensis (Bt), an organic product that gives hornworms a deadly bellyache.

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Symptom: Small, jumping bugs chewing hundreds of holes in the leaves.
Culprit: Flea beetles are a danger to seedlings, gnawing through leaves fast enough to kill small plants.
Cure: Vacuum leaves with a low-power vacuum to remove the bugs, then dust plants often with diatomaceous earth, a powder made from crushed fossilized diatoms that repels insects. Tip: Empty the vacuum right away, because the beetles are still alive in there.

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Symptom: Leaves turning yellow with purple veins. Fruit is small and tasteless, and the plant looks like sugar was spilled on it.
Culprit: Small, sap-feeding psyllid insects deposit saliva that causes the plant to grow oddly. Look underneath the leaves for the scale-like nymphs. Their waste, called lerps, looks like sugar.
Cure: Tiny psyllids can cause big problems for tomatoes, severely stunting the fruit. At the first sign of these bad bugs, spray with insecticidal soap or dust plants with sulfur.

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Symptom: Green plants starting to yellow from the bottom up. Older leaves have brown spots with concentric rings, and sometimes the stems or fruit are blemished.
Culprit: Early blight is a fungus spread by water, insects and gardeners.
Cure: Pick off diseased leaves and keep the ground free of debris. Dust healthy leaves with sulfur to shield them from infection. Give plants room to grow without crowding, and use drip irrigation to prevent splashing water.

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Symptom: Black, sunken, rotten spots on the bottom of the fruit.
Culprit: Blossom end rot, which is caused by poor calcium uptake. Though calcium is plentiful in our soil, irregular watering and excessive heat prevent the plant from using it.
Cure: Use an irrigation timer to automatically turn on and off the water, and mulch plants to keep the soil from drying out too rapidly.

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Symptom: Fruit with bleached-out soft spots or unripe, green shoulders.
Culprit: Intense sun and high heat are too much of a good thing for tomatoes, causing sun scald, poor fruit set and unripe spots.
Cure: Canopy the plant with shade barrier cloth draped on support poles above the plant.

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Symptom: Limp, wilting leaves that don’t perk up in the evening or after watering. Older leaves yellow and die, and often just one side of the plant is affected. Plant may be stunted with few tomatoes.
Culprit: Fusarium wilt, which blocks the plant’s water-transport system. Some tomatoes are resistant to this disease, but heirloom varieties may suffer.
Cure: Pull and destroy the plant. The problem remains in the area for several years, so plant your tomatoes, eggplant, potatoes and peppers in another spot for the next three seasons.

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Symptom: Mottled yellow and green leaves, or leaves with purple spots. Plants are small, yellow and bushy. Fruit has yellow rings and spots.
Culprit: Tomato spotted wilt virus or impatiens necrotic spot virus. Viruses can cause odd-looking problems. If you notice your plant’s leaves elongating like a shoestring, becoming curled or cupped, it may be a virus.
Cure: Viruses can’t be cured, so pull and destroy the plants.

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Symptom: Leaf spirals or looks stretched out, with cupping or distortion.
Culprit: Tomatoes are sensitive to herbicides. Many gardeners don’t spray their food plants; instead, the damage is from drift. Drift can occur from applying lawn weed killer on windy days.
Cure: Limit weed-killer applications to cool times of the day when the wind is calm.