5 Reasons Tomato Leaves are Turning Yellow and What to Do

Have you noticed some leaves are turning yellow on your tomato plants? There are different reasons why tomato leaves may turn yellow. Sometimes it is natural while in other cases, it may be an indication of a serious problem that needs to be investigated.

Yellow spots on tomato leaves can result from a simple thing such as excess or too little water in the soil to something much more serious like nutritional deficiencies, pests, and diseases. Conducting a soil test and examining the plant closely for other symptoms can help to determine the exact cause of yellow spots on leaves.

Tomato leaves turning yellow

Why are my tomato leaves turning yellow?

There are several reasons why the leaves on your tomato plant are turning yellow. This includes:

1. Nutrient deficiency

A tomato plant is a heavy feeder as compared to other vegetables and legumes like cucumber or beans. They require plenty of nutrients to grow healthy and produce high yields. Before providing fertilizer to your plants, it is important to carry out a soil test to determine the exact nutrient that is inadequate in the soil.

Tomato plant requires different nutrients to grow healthy. The deficiency of each nutrient will be characterized by different types of yellow spots on leaves.

Identifying where the yellow leaves are located on the plant or which part of the leaves is affected will help you to identify the exact nutrients that your plants require. Deficiency of the following nutrients may result in yellow spots on tomatoes:

  • Nitrogen deficiency: Nitrogen deficiency is characterized by yellowing of the whole leaf. Older leaves that are on the lower plant are the most affected. The plant uses the little nitrogen it gets from the soil on the young upper leaves and hence they remain green.
  • Potassium deficiency: Potassium deficiency causes the outer part of tomato leaves to start yellowing before turning brown and eventually looking burned.
  • Magnesium deficiency: If your tomato plants’ leaves are turning yellow but the veins are remaining green then it means that they are suffering from magnesium deficiency.
  • Calcium deficiency: Calcium deficiency also causes yellow leaves in tomatoes. It is also characterized by blossom end rot. This is whereby tomato fruits will start to develop a brown spot at the bottom that turns black and may start to rot.
  • Iron Deficiency: Inadequate iron in the soil can also cause tomato leaves to turn yellow with green veins.

2. Diseases

Tomato plants are prone to different diseases. Yellow leaves may be one of the symptoms to look out for. Some of the common diseases include:

  • Early blight: This is a fungal infection that causes bulls-eyed-shaped brown spots on older leaves at the lower part of the plant. Leave tissues surrounding these spots to turn yellow color. Eventually, the affected leaves fall off from the plant.
  • Late Blight: Late blight is a very dangerous tomato disease that attacks the plant from the upper leaves. It is characterized by large and oil-looking spots on the leaves and stem. White mold may appear on the margins of spots on the affected parts.
  • Sectorial Leaf Spot: This is also a serious disease that commonly affects tomato foliage and stems. It is a fungal infection that affects leaves on the lower part of the tomato plant. The affected leaves turn yellow before falling off from the plant.
  • Leaf Mold: This is also a fungal infection that affects the lower leaves of tomato plants. It affects leaves that are near the soil where air circulation is poor together with high humidity. The leaves start by turning pale green or yellowish before turning completely yellow.
  • Bacterial spot: Bacterial spots can also cause tomato leaves to turn yellow. It is caused by different species of bacterium xanthomonas. It is more common in green tomatoes as compared to red tomatoes. Tomatoes are prone to bacterial spots, especially during the wet season. The other symptoms of this infection include numerous water-soaked spots on leaves and raised spots on fruits.
  • Fusarium wilt: This is a fungal infection caused by the fungus Fusarium oxysporum. It is common in warm weather, it causes the lower leaves of your tomato plant to turn golden yellow, droop, or wilt, and eventually death of the whole plant. It is a soil-borne disease that enters the plant through the roots.
  • Verticillium wilt: Tomato plants affected by verticillium wilt usually exhibit yellow and brown spots from the middle of veins of the leaves and spread to the edge. Unfortunately, this disease has no treatment but it can be managed by uprooting the affected plant before spreading to others.

3. Pests

Pest infestation in your tomato garden can also cause yellow leaves. Pests that commonly affect tomatoes are aphids, spider mites, flea beetles, whiteflies, hornworms, and cutworms. Most of these pests feed on tomato leaves hence causing part of them to change into a yellow color.

4. Excessive or too little watering

Watering problems such as too much or too little water can cause your tomato leaves to turn yellow. Water-soaked soil may also harbor diseases that can also cause yellow leaves on your plants. Inadequate moisture in the soil can cause plant leaves to wilt and turn yellow before falling off.  

5. Transplant shock

Is your young tomato plant leaves turning yellow after transplanting? If yes, then they may be suffering from transplant shock. In the first few weeks after transplanting your tomato plants from nursery beds into the main field, you will notice some changes in the leaves’ color as the plant adjusts to the new conditions.

How to fix yellow spots on tomato leaves

If you fail to treat or prevent the underlying cause of yellow spots on tomato leaves, it can kill the whole plant or spread to other nearby plants. There are several options you can use to treat or prevent the yellow spots:

  1. Use proper watering techniques. Avoid underwatering or overwatering your tomato plants. Apply water at the base of the plant near the roots and not on the foliage.
  2. Get rid of the diseased leaves and dispose of them properly or burn them off. If the whole plant is affected, uproot and burn it. It helps to prevent the disease from spreading to other healthy tomato plants in your garden.
  3. Apply mulch in your garden or under your plants. Mulching prevents leaves and fruits from touching the soil and hence prevents some soil-borne diseases from affecting your plants. Some fungus stays in the soil and can easily be transferred to the plant through water splashes from the soil when watering, mulch helps to prevent such scenarios.
  4. Get rid of weeds in your garden. Some weeds especially the nightshade family are perfect hosts of pest and diseases that commonly affects tomato plants.
  5. Stake or cage your tomato plants early. It helps to prevent the leaves and fruits from touching the soil that may be harboring pests and diseases.
  6. Ensure that your plants are spaced well. Over-crowding prevents free air flow between plants. Overcrowding and humid conditions provide ample conditions for the spread of various diseases like early blight in tomatoes.
  7.  Practice plant rotation. Planting tomatoes over and over again in one place encourages the breeding of pests and diseases that may attack your plants. It is also important to avoid growing tomatoes where the previous plant belongs in the same family.
  8. Apply a solution of Epsom salt once every two weeks. Tomato plants are heavy feeders but prone to magnesium deficiency as compared to other vegetables.
  9. Use insecticidal soaps or horticultural oil like neem to get rid of small pests such as aphids, whiteflies, spider mites, and flea beetles. Pick and kill large pests like hornworms and cutworms.
  10. Fumigate the soil to get rid of pests and diseases before planting your tomato plants.

Should I remove the yellow leaves on the tomato plants?

Yes, you should remove yellow leaves from tomato plants especially if they are caused by fungal, bacterial, or viral infections. Cut off the affected leaves at the earliest sign. The longer they stay on the plant, the higher the chances of spreading the infection to other parts or other plants.

It is also important to dispose of properly the affected leave. The pests may crawl back to a new plant if the affected leaves are disposed of within the garden. It is recommended to burn them.

Final Thoughts

If you are planning to have high yields and quality tomatoes, it is important to ensure the plant remains healthy with green leaves throughout. Yellow leaves are an indication that your plant is not healthy. It may be suffering from nutritional deficiency, pests, diseases, or poor management.

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