Common Tomato Plant Problems – Let the Leaves Tell the Story

Growing tomatoes in a home garden is a popular hobby for millions of people around the world. Why?…because there is NOTHING like a fresh, juicy tomato from your very own garden.

Unfortunately, tomato plant problems are also very common. Problems may include harmful insects, diseases and improper care or fertilization. It doesn’t matter whether you grow your tomatoes in a garden, in a pot, on your deck, upside-down, right-side up or sideways, most tomato plants can fall victim to any or all of these problems.

The leaves of your tomato plants are a great early indicator of potential problems. Regular, weekly inspection of your tomato plant leaves will allow you to notice changes early and detect problems while they can still be easily controlled. If a problem is allowed to go undetected, it may become incurable and result in a total loss of the plant or crop.

Yellow leaves

Symptom: Yellow, uncurled leaves begin to form at the bottom of the plant and may work their way up the plant.

Cause: Yellow leaves are a common problem and may be caused by many things. If yellow, uncurled leaves appear at the base of a tomato plant, it may just be a sign of the plant aging and beginning to die off from the bottom up. It may also be caused by a nitrogen deficiency in the soil.

Other factors may cause yellow leaves including pest, fungus and bacterial infestations but these causes usually result in deformed or curled yellow or brown leaves. For example, if the leaves are turning yellow or brown higher up on the plant, it may be a sign of early or late blight. Have your soil tested at a local nursery to confirm the nitrogen-deficiency diagnosis.

Remedy: If the soil does have a nitrogen deficiency, supplement the soil with well-rotted manure or compost, both of which are high in nitrogen. You can also apply a nitrogen-rich fertilizer. If the soil test results do not show any deficiencies, continue to explore other causes including wilt or blight.

Shiny, sticky, deformed leaves

Symptom: Leaves are deformed, sometimes yellow, and appear to have a shiny, sticky substance on them. Young tomato plants are especially vulnerable to this “small” problem. Do not confuse this with “rolled” leaves which is a normal occurrence and not harmful to many tomato plants.

Cause : Aphids are small, pear-shaped insects that congregate on the top growth or underside of leaves. Aphids damage tomatoes by sucking plant sap and excreting a sticky substance on the foliage and fruit. Inspect the deformed leaves or normal leaves in the vicinity and you should be able to see these insects.

Whiteflies and spider mites are also nearly invisible insects that can cause similar symptoms. Spider mites cause small yellow specks and fine webs on leaves. Whiteflies will actually take flight when you brush the plant.

Remedy: Use an insecticidal soap or general-purpose garden dust to control any of these insects.

Brown patches on leaves

Symptom: Black or brown spots develop on plant leaves and they begin to fall off the plant. The plant may also produce fruits with a sunburned appearance.

Cause: Early Blight is a fungus that survives during the winter on old vines left on the garden floor. Cleaning up old vines from the prior season, rotating crops and spacing plants properly to allow for good air circulation are good first steps in avoiding this problem.

Remedy: Preventative measures should be considered first, ie. crop rotation and cleaning up debris from prior growing seasons. If you suspect your plants have Early Blight, remove all diseased stems and foliage and dispose of in the trash. Do not add the plant debris to your compost pile. A general-purpose garden dust can sometimes be effective in controlling the disease if caught in the early stages.

Brown, dry, papery leaves

Symptom: Water-soaked patches appear on leaves that ultimately turn brown, dry and papery. Fruit and stems might also be spotted or have blackened areas.

Cause: Late Blight is caused by a fungus that is favored by wet weather and whose spores can travel great distances and infect large areas.

Remedy: Late Blight can be prevented or controlled in a similar fashion to Early Blight as described above. If the area is severely infected, removing all plants and disposing in the trash may be the only solution.

Large sections of suddenly wilted leaves and stems

Symptom: Fusarium Wilt causes leaves on one branch of infected plant to wilt and turn yellow. Verticillium Wilt first appears as yellowing between the major veins on mature leaves.

Cause: Both wilts are caused by a fungal infestation. The fungus is inherent in the plant and is not caused or affected by external sources such as weather or care.

Remedy: Unfortunately there is no treatment for a plant infected with Fusarium or Verticillium Wilt. It will spread rapidly through the plant and eventually kill it. The best remedy is to quickly dispose of the entire plant in the trash. Do not add the debris to your compost pile. To limit the risk of wilt reappearing in the future, seeds or seedlings should be selected carefully. Many varieties are resistant to wilt and although it doesn’t guarantee it won’t occur, it significantly limits the risk.