From Gardener's Supply (www.gardeners.com)

Troubleshooting Tomato Problems

What's wrong with my tomatoes? Learn how to diagnose and treat

tomato hornworm
tomato hornworm

Fresh, vine-ripened tomatoes are one of the great joys of summer. However, sometimes diseases, pests and/or environmental stresses get in the way of our tomato harvests.

The best way to avoid tomato troubles is to start with healthy plants. They are better able to fend off diseases and pests than stressed or weak plants. Choose a planting site in full sun and keep the soil evenly moist throughout the season. Provide a steady source of nutrients, too. At planting time, add a granular fertilizer that's made for tomatoes, such as our Gardener's Best Organic Tomato Fertilizer. During the growing season, treat your plants to a water-soluble fertilizer, such as Plant Health Care.

Even the best-cared-for plants can be plagued by problems. Diagnosing the culprit is the first step — is it a disease? An insect? An environmental condition? Here are some of the most common tomato problems and recommended solutions. Keep in mind that problems with your tomatoes will depend on many factors, including your soil and climate, as well as localized disease and insect pest outbreaks.

Signs and Symptoms

Fruit with black sunken areas on the blossom end are a sign of blossom-end rot. Although it looks like a disease, blossom-end rot is caused by a calcium deficiency, usually aggravated by drought or uneven watering, root damage and/or excess nitrogen. Fortunately, blossom-end rot will usually occur on just a small number of fruit, especially at the beginning of the harvest season. To prevent it, provide sufficient water to plants to keep soil moist throughout the growing season and apply a thick layer of straw mulch to help conserve soil moisture. You can also combat the problem with a ready-to-use spray called Rot-Stop, which is an all-natural formula for blossom-end rot. More information on blossom-end rot.

Blossom-end rot
Blossom-end rot. Photo: Susan Romanoff

If few flowers form on your tomato plants or the flowers drop before setting fruit, possible causes include

  • Nighttime temperatures above 70 degrees F or below 50 degrees F
  • Daytime temperatures above 85 degrees F
  • Drought stress
  • Excess nitrogen
  • Too little sun

The most common cause is temperature, so the problem usually resolves itself when weather improves.

Dark, concentrically ringed spots that cover the lower leaves and stems are a sign of early blight.

To prevent and control the spread of blight, spray with Actinovate or Copper Fungicide. Also, limit the spread of the disease by not getting water on the leaves when watering and not handling plants when they are wet.

More information on early blight.

Early blight on tomato leaf
Early blight disease on a tomato leaf, indicated by the concentric rings.

Water-soaked patches and lesions on stems, foliage and fruit are signs of late blight. Outbreaks spread quickly under favorable conditions because the pathogen can produce huge numbers of wind-dispersed spores. Track outbreaks on the map at usablight.org.

When late blight is detected in your region, consider preventative spraying with Actinovate or Copper Fungicide.

Late blight
Late blight disease can manifest as blackened stems and foliage.

Holes chewed in leaves and fruits can indicate the presence of a tomato hornworm. This large caterpillar has white diagonal stripes and a black horn projecting from the rear. Handpick these caterpillars (drop them in soapy water as you pick them). More information on tomato hornworm. Holes chewed in tomatoes can be the work of slugs. There is nothing worse than picking a tomato and finding a slug happily working its way through it. Slugs can be thwarted with iron phosphate-based slug pellets and beneficial nematodes.

More information on slugs.


Tomato hornworm
The tomato hornworm is relatively easy to control.

Small holes in fruit and tomatoes that collapse when you pick them might be the work of tomato fruitworms. These moth larvae bore into fruits and consume them from within. Once the larvae are in the fruit, the only remedy is to destroy the infected fruit. If fruitworms are a severe problem in your area, start the plants under row covers and keep them covered until they flower.

Cracks in fruit are generally caused by uneven watering. Use a soaker hose or irrigation system, to apply water directly to the soil, moistening the entire root zone each time you water. Apply mulch to help retain moisture.

More information on cracking and catfacing.

Yellowed, distorted and curled leaves may be a sign of an infestation of aphids. Check for aphids on the undersides of leaves or clustered on new growth. Aphids are easily controlled with a strong jet of water or an application of neem oil. More information on aphids. Distorted, yellowed leaves can also signal tobacco mosaic virus. To prevent tobacco mosaic virus, wash hands thoroughly after smoking or using other tobacco products before heading to the garden. Infected plants should be removed and discarded (not composted).

Wilting foliage might be a sign of insufficient water. But if the lower leaves are wilted and plants are stunted and do not recover after watering, fusarium wilt is likely the cause. Infected plants should be removed and discarded (not composted). More information on fusarium wilt.

Troubleshooting tips for tomato problems
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Last updated: 2/26/19


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