Causes and Solutions to Tomato Plant Leaves Turning Yellow


Tomato plants are a staple for gardening enthusiasts since they are easy to grow and do not require much space. However, the most common problem you are likely to face is the tomato plant leaves turning yellow. The issue can have many causes, treatments and forms of prevention that you need to learn to ensure a bumper harvest.

1. Diseases

Gardening and caring for tomato plants is a constant battle against diseases that cause their leaves to turn yellow. Below is a breakdown of the causes, symptoms, treatment and prevention measures against the pathogens that spread through the soil.

a). Fungal Diseases

As a preventative measure against early blight, septoria leaf spot, Fusarium wilt and Verticillium wilt, ensure you practice strict crop rotation by alternating the tomato plants every two years. This step will help reduce the chances of these diseases reappearing.

Additionally, you can use mulch that comprises newspapers, straws or wood chips since these will prevent the early blight fungus in the soil from splashing on the plants. Finally, you can water your garden carefully to avoid getting water onto the leaves or watering the tomato plants in the morning. This move will facilitate the growth and spread of the septoria leaf spot and early blight. Plus, buying a top-notch Copper Fungicide can help with treating these diseases.

Fusarium wilt and Verticillium wilt are more difficult to prevent as the fungi remain in the soil for long periods. However, soil solarization, planting fungus-resistant tomato plant varieties and decent garden hygiene can help you avoid these diseases.

1. Early Blight

When it comes to the early blight fungal disease, preventing the issue is the best way to treat it. The condition strikes early in the growing season, and it is characterized by older leaves at the base of the plant having yellow splotches that turn into brown spots with a yellow circle surrounding them. Plus, the fungus will continue spreading until the whole leaf turns yellow.

If early blight is why tomato leaves in your garden turn yellow, you need to act fast before losing the entire plant. First, remove the affected lower leaves and dispose of them as recycling them into a compost might propagate the disease further. Next, mulching the garden and applying fungicides will help curb the issue.

2. Septoria Leaf Spot

Septoria leaf spot, brought on by the soil fungus Septoria lycopersici, causes yellow spots on the bottom of the older leaves. Eventually, the circles will enlarge with a dark brown outer layer, a tan middle and a yellow ring around them. Finally, when the leaves have been entirely covered, they fall and leave the developing fruit exposed as the disease spreads up the stem. Plus, the plant will lack the ability to continue budding since all the yellow tomato leaves fall off.

Fungal diseases should be dealt with immediately by pruning and proper disposal of the yellowing leaves. A dash of baking soda mixed with a gallon of water then generously sprinkled on the tomato plants should work on the fungus. Alternatively, you can buy hydrogen peroxide and add water in the ratio of 1:5 every four days until the garden recovers.

3. Verticillium Wilt

This soil fungus thrives in colder regions that cause the tomato plants to wilt when harvest time rolls around. Next, the bottom leaves turn yellow from splotches that have brown veins spreading from them. Eventually, dark brown spots will develop, and the leaves will fall off, stunting the growth of the tomatoes.

Although the symptoms of Verticillium wilt are similar to early blight, you can differentiate them by checking for the yellow ring that shows up in the latter disease. Furthermore, Verticillium wilt has no chemical treatment measures, and proper disposal of the entire plant is necessary to stop the fungus from spreading.

4. Fusarium Wilt

The Fusarium oxysporum, the fungus that causes yellow leaves on tomato plants, makes the crop wilt on one side. This disease begins at the bottom of the stem and spreads through the leaves to the flowers and tomatoes. Plus, the fungus is more prevalent in warm areas where the soil temperatures can accommodate it.

Treating this disease is not an option, so as soon you see tomato leaves turning yellow, and you identify the problem as Fusarium wilt, remove the whole plant and throw it in the trash. Remember to act before it spreads immediately.

b). Bacterial Wilt

The Rolstonia solanacearum bacterium, more common in coastal regions where the sandy soil is moist, makes the plant symptomatic as the tomatoes ripen. If you damage the roots when transplanting, the bacteria can enter the root system and cause leaves to turn yellow. You can identify the problem by observing the distinct v-shaped indents on the yellow leaves.

Eventually, the tomato plants will die, but the process will happen more slowly if the weather conditions are colder and drier than what the bacteria likes. Unfortunately, you cannot treat this disease. Instead, remove the affected plants and ensure the yellow tomato leaves do not contact the healthy ones.

You can look for plant varieties that are resistant to this disease. Alternatively, space out your tomato plants to improve air circulation in the soil. In addition, crop rotation and keeping your garden clean can help with prevention.

2. Pests

Pests that feed on leaves on tomato plants cause them to turn yellow. Aphids and mealybugs are commonly found on the stem or the bottom of leaves. You can use natural treatment methods like introducing ladybugs or spray the tomato plants with a soapy solution. You can buy the Bonide Neem Oil Spray since it is an excellent natural insecticide against these pests.

3. Environmental and Growth Factors

Taking care of your garden by tending to the soil and ensuring favorable conditions for the crops helps improve your harvest. Hence, if you observe tomato plant leaves turning yellow, you can start by checking for the issues below.

a). Transplant Shock

Transplant shock occurs when seedlings are transferred from a consistent environment to one where conditions fluctuate. You can identify the issue as soon as a week after you transplant the seedlings when the green leaves begin to turn yellow. Still, if you observe that the leaves at the top of the plant continue growing, the problem may be temporary.

Dissolving about 5 grams of regular sugar in a gallon of water then spraying on the garden is a popular yet unproven solution to reviving affected seedlings. Then, over a week, you can slowly introduce the plants to the external environment and put an overhead cover if the days are too hot.

b). Lack of Sunlight

Except for some cherry tomato varieties thriving on 6 hours of sunlight, most alternatives require more than 8 hours. If the tomato plant is not receiving enough sunshine, you may observe yellow leaves if you have planted them in a shaded area. Since developing tomatoes depend on the sun’s light to mature, you can remove any barriers to the sunshine by clearing other plants and weeds around the crops. Buying a raised and movable garden can help you maneuver it to well-lit areas during the day.

Alternatively, the yellowing leaves on tomato plants can be a natural process if only the bottom ones are affected. Thus, it could be nothing to worry about when the crop’s growth remains healthy and productive. Still, you can buy a quality sunlight tester to ensure your plants get the recommended amount of sunshine.

c). Nutrient Deficiency

Tomato leaves turning yellow may be due to a lack of essential nutrients like iron and nitrogen. You can buy chelated liquid iron to boost the content of the former in your garden, and the product can also help with root damage. Worm castings  are excellent organic fertilizers that increase the amount of nitrogen in your garden, but compost or coffee grounds will suffice. Before you make a purchase, it is crucial to find out how you can identify a lack of these nutrients in your soil.

1. Nitrogen Deficiency

When the plant’s lower leaves start turning pale yellow, while those on the top remain green, it may be a sign of nitrogen deficiency. To differentiate this problem from the natural wilt of the first leaves, you need to observe a halt in the growth and production of fruit. Then, carefully add fertilizers rich in nitrogen to treat the issue without causing more harm to the plants.

2. Iron Deficiency

If the youngest leaves begin yellowing at the base and the color spreads through the veins until the entire leaf is pale yellow and falls, the issue may be iron deficiency. Merely introducing iron as a supplement to the soil will solve the issue. However, you need to follow the instructions when dealing with fertilizers, as an improper application could cause more damage.

d). Issues with Watering

Yellow leaves on a tomato plant could be a result of either overwatering or underwatering your garden. During the growing season, tomatoes demand plenty of water but overdoing it will make it difficult for oxygen to circulate through the soil. As the roots suffocate because of too much water, the leaves turn yellow.

Carefully remove mulch at the bottom of the plant to increase air supply and evaporation of excess moisture from the soil. Only adding the prescribed amount of water to your garden involves reliably measuring the moisture content in the soil and setting up an automated drip irrigation system

On the other hand, if you are underwatering your garden, the plant will wilt, and the leaves will turn yellow. The yellowing will start from the edges and spread throughout the leaves until they become pale yellow and fall off.

You should try to slowly water the soil, if it is too porous, to give the roots enough time to absorb the moisture. A quality drip irrigation system can solve this problem, especially when it is automatic.

e). Soil pH Levels

Maintaining the right pH for the soil allows the plant to absorb nutrients well. Adding too much fertilizer can increase the pH of the soil to levels that hinder the plant’s growth and cause yellow leaves that may eventually turn brown. Ensure you diligently follow the instructions for adding fertilizers to avoid negatively altering the acidic and alkaline conditions in the garden.

Frequently Asked Questions (FAQs) on Tomato Plant Leaves Turning Yellow

1. How do you fix yellow leaves on tomato plants?

Yellow leaves on tomato crops could be a result of numerous factors. Therefore, identifying the problem should be your priority, as you can figure out the best course of action once you have a clear understanding of what you are dealing with. Luckily, most of the yellowing leaves issues have quick fixes and may be nothing to worry about.

2. Should I remove yellow leaves from a tomato plant?

If a fungal or bacterial infection is responsible for the plants’ leaves yellowing, you should remove and dispose of them immediately. These diseases can spread via contact, and leaving the affected lower leaves on the plant will compound the situation.

3. Why are the leaves on my tomato plant turning yellow?

Yellowing leaves on your tomato plant may not be a cause for alarm if you are coming to the end of the season. However, you may need to hasten the ripening process of the tomatoes before the days get too short and the nights get too long and cold for them to continue growing. First, prune the yellow leaves and remove any tiny fruit or new bud. This move will redirect plant resources towards the ones already growing, and they will reach maturity before you run out of time.

4. What are the signs of over-watering tomato plants?

If you see a tomato fruit cracked or yellowing, blisters or humps on the lower leaves, you may be adding too much water to your garden. The roots will begin to rot as the soil is not receiving enough oxygen. Trimming off the yellow leaves and removing mulch can help with removing excess water and aerating the soil. 

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