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Tomato Leaves Turning Black – Why?

Tomatoes are very low-maintenance plants and are grown in almost every country of the world. 

In fact, tomato seeds are currently being developed to be grown in space!

However, these plants don’t come without complete difficulty. 

If you notice your tomato plant’s leaves are turning black, this means that your plant needs attending to as soon as possible. 

Read on to diagnose the problem, and learn how to cure it!


Why are Tomato leaves turning black?

If your tomato plant has leaves that are turning black, they most likely have a disease such as late blight, bacterial speck, or bacterial canker. A common disease also is septoria leaf spot leading to tomato leaves turning black. Diseases can be treated using chemical or natural fungicides and can be prevented by purchasing disease-resistant seeds and practicing cleanliness when handling tomato plants.


Reasons why tomato leaves turn black


Late blight

Blight is a disease that has been known to frustrate and puzzle gardeners all over the world. It spreads rapidly and can wipe out a whole field of crops in a very short amount of time.

There are two different forms of blight: late blight and early blight. Late blight displays symptoms of dark spots on the edges of your tomato plant’s leaves, whereas early blight does not.

These dark patches may even grow towards your tomato plant’s stem. Small dots of white mildew may also grow on the infected areas. 


Bacterial speck

Bacterial speck is a common plant disease that occurs around the world regardless of the environment or temperament. 

Symptoms include small black spots around the surface of the leaves, that are mostly more prominent on the undersides. 

These spots can sometimes have a yellow ring them, especially if the plants are more mature and these spots can be raised or sunken in to touch. 

Unlike most tomato plant diseases, bacterial speck also affects the tomato fruit. As the disease progresses, black spots will begin to grow on the skin of your tomatoes. 

Eating fruits infected by bacterial speck can cause illness, and it is suggested that no fruit that appears to be discolored is consumed at all. 


Bacterial Canker

Bacterial canker is a disease that attacks the fruits, foliage, and stems of a tomato plant. 

Symptoms include discoloration of the leaves, beginning with the tips becoming brown and crispy, and as time progresses the veins and centers of the leaves will turn a black or brown color. 

The stems will also turn black if left untreated, and the tomato fruits themselves will grow white spots

Often it is the case that bacteria canker has come from an infected tomato seed. This disease spreads very rapidly, and just one infected plant could wipe out a whole greenhouse of crops.

Unclean gardening tools or pots that have not been cleaned before use can also spread this disease.

It is important to practice cleanliness when handling your tomato plant to prevent infections. 


Septoria leaf spot

Septoria leaf spot is a fungus that predominately affects the leaves of a tomato plant. 

Early symptoms include yellow spots appearing on the undersides of older leaves, that will eventually turn a dark blackish brown. 

Another identifying feature is the spots having a light brown halo around them.

From here, the leaves will become dry and limp, before completely falling off. 

Septoria is usually caused by your tomato plant being too moist; maybe a result of heavy rainfall or overwatering. 

A severe bought of septoria leaf spot can leave a tomato plant completely unable to bear fruit, as it has become too weak and damaged.


How to treat black tomato leaves

There are many fungicides on the market to treat tomato leaves that are turning black, many of which specialize in treating specific kinds of diseases.

These can be purchased from garden centers and plant nurseries, and usually need to be diluted and then sprayed directly onto the leaves. 

If you would prefer to use a less harsh and more natural solution, you could choose to create your own fungicide. 

Mix 1 teaspoon of baking soda with 4 cups of lukewarm water, and add in a drop or two of liquid soap. 

Spray the solution all over your plant and its leaves, and repeat once a week until you start to see signs of improvement. 


Preventing tomato leaves from turning black

One way to prevent tomato leaves from turning black is to choose varieties of tomato plants that have been created to be resistant to disease. 

For example, some tomato seed packets will state that they are blight resistant.

It is also suggested that you don’t plant your tomatoes in the same area every year, and especially not when you’re planning to use the same soil

If you plant your tomato plants in pots, be sure to bleach the pots thoroughly after the season is over. 

Diseases can harbor themselves in soil and stay dormant during the winter seasons, ready to pounce on your new crops the next season. 

Some gardeners even go a step further in making sure that their plants are protected from disease. 

Washing your tomato seeds in hot water (around 120 degrees Fahrenheit) for 30 minutes before planting can kill diseases that are living on them. 


Frequently Asked Questions about Tomato Leaves Turning Black


Should I cut black leaves off of my tomato plant?

If only a small number of leaves have begun to turn black, you could cut them off in an attempt to stop the rest of your leaves from being affected. If most of the leaves are black, avoid pruning them and try other methods instead.

Author Bio

Daniel Iseli

Taking care of houseplants and gardening are my greatest passions. I am transforming my apartment into an urban jungle and am growing veggies in my indoor and outdoor garden year-round.