9 Reasons Your Tomato Leaves Have White Spots on Them (and What to Do)

Tomatoes are one of the most popular crops grown by home gardeners. They also are commonly affected by pests and diseases caused by fungal or bacteria infections. If your tomato leaves have white spots on them, it can signify that your tomato plant is stressed and struggling.

There are various reasons why there might be white spots on your tomato plant leaves, and it’s important to determine the root cause in order to treat the problem properly. These are the most common diseases and pests that could be the cause, as well as how to fix them.

Powdery Mildew

Tomato plants do not like when water sits on their leaves. If you live in warm climate or have received a large amount of rain recently, it can lead to a fungal disease called powdery mildew. It is one of the most widespread and easily recognized plant diseases. As its name suggests, powdery mildew is characterized by white, powdery spots or patches commonly found on the upper sides of the leaves.

How to Fix Powdery Mildew

Fortunately, powdery mildew is rarely fatal to a tomato plant, though it can affect its health. Its appearance is usually worse than the damage caused. To treat powdery mildew, remove the affected leaves and prune your tomato plant to improve air circulation. You can apply a fungicide—look for one containing potassium bicarbonate, neem oil, sulfur, or copper—or mix up a homemade spray to control the spread of powdery mildew.

To prevent it from returning, water your tomato plants directly at the ground level, avoiding getting the leaves or fruits wet.

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Nutritional Deficiency

Nutrient deficiencies often present themselves on the leaves of tomato plants, which require a lot of nutrients for proper growth and fruit development. If there are spots on older leaves that are yellowing or whitening, it could indicate a lack of nitrogen, phosphorus, calcium, or magnesium in the soil.

How to Fix Nutritional Deficiencies

For a quick fix, give nutrient-deficient tomato plants a boost by applying a seaweed liquid feed. Dilute one capful in a watering can and apply to the leaves once a week. To determine the exact deficiency in the soil, it’s best to conduct a soil test.

Tomato Blight

Blight is a potential devastating disease that can affect a number of different plants, including potatoes and tomatoes. This fungal disease can affect tomato leaves, as well as stems and fruits.

One of the first symptoms of blight are shriveling leaves that have a white fungal growth on their undersides. It is more commonly found on tomato plants grown outdoors; greenhouse tomato plants are less frequently affected.

How to Fix Late Blight

If the tomato blight is minimal, remove all affected tomato leaves and clean any gardening equipment that might have come into contact with the plant to prevent disease transfer. However, picking off the leaves won’t get rid of the problem.

To ensure that blight is fully eradicated, removing the plant and applying a fungicide to the area is your best option. Rotate your crops and plant tomatoes in a different area next year to prevent its return, as blight can overwinter on plant debris and in the soil.

Sun Scald

Tomato plants need heat and sunlight to produce fruit, but too much of it can cause the tomatoes and leaves to be scorched. Known as sun scald, this occurs when a plant is exposed to direct rays of sun during hot weather, and both the fruit and the leaves can be affected. Sun scald in tomato plants can appear as white or brown spots on the leaves.

How to Fix Sun Scald

There’s not much you can do once sun scald sets in. The best way to treat sun scald is to prevent it from happening in the first place. Pruning your tomato plant can help promote fruit growth, but it can also expose the plant to too much sunlight. Make sure to not overdo it. If there’s extreme heat ahead in the forecast, put up a shade cloth to protect the plants.

Whitefly Infestation

It will be easy to tell if your tomato plant is infested by whiteflies: dozens of these tiny, heart-shaped flies will emerge in a cloud when the plant is bumped or disturbed. These pests prefer to feed on new growth and can stress the host plant.

How to Fix a Whitefly Infestation

There are a number of ways to control whiteflies. Start with mechanical options, such as using a garden hose to strongly spray the plant with water, applying sticky traps on the infected plant, and spraying the plant with a premixed insecticidal soap or neem oil.

If the problem persists, add companion plants to attract beneficial insects or add reflective mulch (which often include silver or aluminum) to help deflect whiteflies.

Mealybug Infestation

Mealybugs are the bane of any houseplant owner’s existence, but they are a common pest on outdoor plants too. A cousin to whiteflies, mealybugs and tiny, white insects that cluster together in cottony masses on leaves—especially areas of new growth. If left untreated, affected plants can die.

How to Fix a Mealybug Infestation

You can manage small mealybug infestations with a spray of water from a garden hose. For more extensive problems, spray the tomato leaves with neem oil, which won’t affect beneficial bees. You can also dip a cotton swab in rubbing alcohol and wipe the leaves directly to kill mealybugs.

Leafminer

Leafminers are the larval state of various insects which burrow into the leaves of plants, including tomatoes, to feed on them. The larvae can be white, yellow, brown, or light green, and worm-like in appearance, eating the cells of the tomato leaves as they go, This will leave a squiggly line of dead, whiteish tissue behind.

How to Fix a Leafminer Infestation

First, remove any tomato leaves that have been affected by the leafminers. To prevent them from spreading to other areas of the plant, apply neem oil. If the problem persists, you may want to resort to using insecticides.

The best way to control leafminer damage to your tomato plant is to catch it early. Always be looking for signs of leafminer damage, as well as their eggs, which can be removed and destroyed before they hatch into destructive adults.

Salt Buildup

Mineral and fertilizer salt deposits on tomato plants typically appear as white crystallized residue on the leaves. A salt buildup can be caused by watering your plants with hard water that is high in calcium carbonate, sodium, and/or iron. Watering tomato plants with water that has a high salt concentration will cause an imbalance in the plant, causing it to improperly grow or die.

How to Fix Salt Buildup

The best way to deal with a salt buildup is by leaching or flushing the root zone of the plant. First, test the water you are watering the plant with to ensure it is low in ions. Then, apply a relatively large amount of water to help dissolve the salt buildup in the soil.

Tomato Mosaic Virus

A common disease that affects tomato plants is tomato mosaic virus (ToMV), a plant pathogenic virus that is found worldwide. It can cause the foliage and leaves of the plant to show mottled, yellowish-whiteish areas with a blister-like appearance. It can spread easily, including on contaminated clothes and tools.

How to Fix Tomato Mosaic Virus

Controlling tomato mosaic virus can be difficult, and there is no cure once the plant is infected. If you believe your tomato plant as been affected, immediately pull it from your garden and burn it or throw it away. Monitor the rest of your plants to ensure it hasn’t spread.