Tomatoes are one of the easily grown, long lasting and productive plants that can be grown during summers. They love the heat and are one of the best plants to grow as a beginner in gardening. The plants require very little care and produce fruits in a short span of time. Home grown tomatoes, if taken proper care can produce really sweet fruits. These plants can be easily grown from seeds or can be transplanted from seedlings bought from nurseries. They have the ability to tolerate the summer heat.

However, yellowing of the leaves is one of the common problems seen in tomato plants. Even a well-cared plant can develop yellow leaves. This can be due to a variety of reasons ranging from nutrient deficiency, watering, pest attract or diseases caused due to fungal or viral pathogens. If left untreated, the plants can develop stunted growth, can delay the fruiting and can also cause the leaves to wilt and fall eventually leading to the death of the plant. It is important to identify and understand the right root cause to treat them. Identifying the problem and providing them the right treatment can rectify the problem and save the plant.

Some of the common causes for the leaves of tomato plant turning yellow:

1. Transplant shock:

Transplant shock is seen usually as the main reason for leaves of tomato plant turning yellow. Plants that are bought from nursery and transplanted into the soil or the seedlings/plants that are re potted goes into the transplantation shock. The term transplant shock refers to the stress that is seen in a newly transplanted plant. The newly transplanted plants might not have well-formed or disturbed root system and can result in stress which prevents the roots from absorbing enough water and minerals. These plants can fall prey to pests and disease-causing pathogens and if not given proper care they can wilt and die.

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Some of the causes for transplant stress are:

Injured root
Lack of proper watering
Unsuitable environmental conditions.
Plants not transplanted properly

Tomatoes are heat loving plants. They need a warm climate to adjust and develop to the new environment. When transplanted during colder conditions, the plants undergo a period of transplant adjustment. The older leaves at the bottom of the plant start to turn lighter in colour and finally turn yellow. However, the young leaves at the top appear green and healthy. Transplant shock can slow down the growth of the plants, reduce the size of the leaves, the size of the internodes thus affecting the size of the branches and can also influence flower formation and fruiting.

Solution: Remove the yellow leaves. Allow only healthy leaves to stay on the plants. The yellow and weak leaves can attract pests and diseases. Water the plants regularly and provide enough water till the plants recover from the shock. Provide proper care to the plants. Transplant the plants late spring when the temperatures are warm.

2. Diseases

Proper sunlight, water, nutrients and temperature are the major parameters required to grow a healthy plant. Even if one of these parameters are compromised, the plants can become weak and can attract disease causing pathogens and pests. This can further reduce the plant health and can also cause death of the plant. One of the major symptoms of most of the fungal and viral diseases are yellowing of leaves. Some of the major fungal and viral diseases that show symptoms of the leaves of tomato plant turning yellow are:

Fungal diseases:

The attack of fungal pathogens can lead to yellowing of the leaves. Some of the diseases that shows yellowing of leaves are:

Early blight:

These are caused by a soil borne fungal pathogen. The leaves develop small yellow spots or lesions which increase in size with time and can appear like a bullseye. They can finally turn brown. The leaves close to the soil are affected first as the pathogens travel from the soil to the plants. They mostly attack plants grown in humid conditions.

Fusarium wilt:

It is caused by a soil borne fungal pathogen. They mostly infect the plants during warmer climatic conditions. The infection leads to the yellowing of one side of the leaf or the plant. Since it’s a soil borne pathogen, the older leaves at the base are infected first which spreads to the top. The yellowing can be followed by wilting, browning and the leaves die and fall. This can also have stunted growth and can affect the flowering and formation of fruits.

Leaf spot:

It is a fungal disease caused by Septoria lycopersici. The infection is seen in plants mostly grown in humid, wet conditions. The symptoms are similar to that of the early blight, but appears mostly after fruiting. The leaves at the base start to develop yellow circular spots with dark brown borders and grey centres. The infected leaves turn yellow, brown wilt and fall. The spots formed are smaller compared to the spots formed in early blight and can be numerous.

The control and cure for most of the fungal diseases are the same.

Prevention: Provide enough aeration between the plants to prevent infections. Remove the leaves from the base of the plants. Do not overhead water the plants and water the plants in the morning such that the excess water evaporates by night. Prune the leaves in case of any thick growth.

Cure: Remove the infected leaves as soon as possible. In case of severe infection or the spread of the infection to the upper leaves, use a mild fungicide. Make sure that the leaves do not touch the soil.

Viral diseases:

Viral infections show varied symptoms one of which being the yellowing of leaves.

Tobacco Mosaic virus:

This is one of the most common viral diseases seen in tomato plants. They can infect different parts like the leaves, flowers and fruit and result in stunted growth. The leaves develop yellow blisters and can curl and die.

Prevention: Protect the plants from pests that can spread the disease. Provide enough aeration to the plants. Prune the leaves in case of thick growth. In case of any signs of infection immediately discard the infected part of the plant and destroy it to prevent the spread. There is no particular cure for viral diseases. The best way to protect the plant from viral infection is prevention.

3. Lack of proper sunlight

The requirement of sunlight usually depends on the variety of tomato plants. But in general, for proper growth of the plant, they require at least 6-8 hours of bright direct sunlight. The lack of sunlight can lead to lightening of the leaf color and can be a cause of leaves of tomato plant turning yellow. It can also can reduce the growth and yield of the plant. Place the plants in spots that have bright direct sunlight.

4. Watering problems

Over watering or under watering of the plant can be harmful to them and can result in a weak plant. Under watering or over watering of the plants can turn the leaves yellow. The leaves at the base as well as on the upper part of the plant can turn yellow together. Water the plants regularly, preferably in the morning. Do not allow water to be stagnant. During hot days, check for the moisture content of the soil mid afternoon or in the evening and water them if the soil is dry.

5. Nutrient deficiencies

Yellowing of leaves can also be caused due to nutrient deficiency, mostly nitrogen. Plants grown in nitrogen deficient soil can develop light green or yellow leaves. Provide enough nutrients to the plant. Fertilise the soil ones in a month.

6. Lack of pruning

The tomato plants usually do not require much pruning but when they are grown together in large numbers, or when the foliage growth is thick, lack of proper aeration and sunlight can attract certain pathogens and also prevents sunlight to reach to the leaves present mostly at the base. Pruning helps in increasing the aeration and provides enough gap to expose the leaves to the sunlight.

Plants Care

Leaves of Tomato Plant Turning Yellow – Know the Top 6 Reasons and Solution