Tomato plants are perfect for both experienced and inexperienced gardeners.
They need a relatively low level of maintenance and are one of the most versatile fruits in the world, and are an important part of many different cultures.
But like all plants, tomato plants still have their issues.
If you notice a dramatic change in the color of your tomato plant’s leaves then is definitely cause for concern.
Black spots on tomato leaves are one of the main signs of disease, so read on to find out what the cause is and how to treat it.
Black spots on tomato leaves
If your tomato plant is suffering from black spots on the leaves, it has likely been affected by disease or pests. In most cases, you can easily cure this with a common pesticide or fungicide. Diseases can also be prevented by maintaining cleanliness when handling your plant.
The causes of black spots on tomato leaves
Septoria leaf spot
Septoria leaf spot is a very common disease in tomato plants. It is something that all gardeners should be aware of, as it is highly likely that they will come across it at some point in time.
Septoria (Septoria lycopersici) is a fungus that affects a wide range of fruits and vegetables, from potatoes to eggplants.
The fungus lives on and in the soil and can be spread through human contact or unsanitary gardening tools.
It spreads quickly, but can be controlled and even cured if caught as soon as possible.
Symptoms of septoria in tomato plants are circular-shaped spots that appear underneath mature leaves. The spots range between light and dark brown and have a faint yellow halo around the edges.
These spots will grow in size over time, eventually merging and taking over the entire leaf.
As septoria progresses, small black patches of moldy fungal spores may also start to grow on the leaves.
If left untreated, the leaves will eventually become dry and limp, causing them to fall off of your tomato plant entirely.
There are various possible reasons for your tomato plant to become infected with the septoria leaf spot.
It could be due to the leaves of your tomato plant becoming too moist, caused by watering your plant from the top of the leaves instead of from the base near the soil.
This makes the undersides of the leaves wet which makes it easier for the septoria to latch onto.
Often, septoria isn’t caught quickly enough. This is because it often attacks the plant from the undersides of the leaves first, making it hard to spot until the disease has progressed further.
If septoria is left untreated for too long, it can result in your tomato plant becoming so damaged that it is unable to bear fruit.
Check your tomato plant’s leaves fully at least once a week, so that you can catch any signs of it as soon as possible.
Blight is another common disease that has been known to frustrate gardeners all around the world. It thrives in moist environments and appears after heavy rainfall.
It can be very detrimental if it is not tended to quickly, and it was in fact blight that caused the infamous and disastrous Irish potato famine back in the 1800s.
Blight has become such a common issue in tomato plants that varieties of seeds have been specifically bred to be resistant to it.
Blight comes in two forms and is unfortunately incurable if not caught very early on.
It is therefore important to know what the symptoms are, so you can catch them early and dispose of your infected plants immediately.
Early blight symptoms
Early blight disease will begin on your tomato plant after fruits have become to grow. Early signs are small dark brown spots appearing at the bottom of the plant’s leaves.
These will grow over time and start to turn into patches that will turn the leaf tissues a yellow color.
Early blight only affects the foliage of the tomato plant and doesn’t directly do any damage to the tomato fruits themselves.
However, the death of the leaves usually goes hand in hand with damage to the fruits.
Having too many leaves fall off of your tomato plant can lead to having not enough shade to protect the fruits during their growing process. Often, this results in them becoming sun-damaged or getting sunscald.
It is suggested that you treat signs of early blight with a copper-based fungicide.
Mix the fungicide with water and spray it on the leaves every few days until you start to see signs of improvement.
Late blight symptoms
Unlike early blight, late blight can affect plants at any point during their growth.
Symptoms include dark spots that appear on the edges of the leaves and grow upwards towards the stem. It spreads fast and can damage your tomato plant until it is too weak to bear fruit.
Over time a white fungus may start to grow on the stems and leaves, which will eventually result in the death of your tomato plant.
Early symptoms of late blight can also be treated with a copper fungicide, but it is additionally suggested that you remove any infected leaves from your plant.
This is because late blight can spread a lot faster than early blight, therefore needing to be controlled as soon as possible to avoid damage to your other crops.
Aphid bug infestation
Aphids are a common pest among a variety of plants, but they are also very common in tomato plants.
Aphids are small bugs that are dark grey or brown in color. Unlike most plant pests, are visible to the human eye, and look like small dots all over the leaves of your plant.
They usually live on the leaves of the plant, although in some extreme cases they can spread to the stems.
Infestations are usually caused by a flying variety of aphids landing on your plant and laying their eggs, but in some cases, the infestation can be spread from other plants.
Aphids feed off of the sap in plant leaves, and excrete a substance referred to as “honeydew”. The honeydew then collects on the leaves of the plant and creates spots of black mold.
These bugs enjoy shady locations, meaning that they will often be found on the undersides of your tomato plant’s leaves.
Over time, they can cause yellowing of the leaves which will eventually lead to curling and will cause your tomato plant to become so weak that it can no longer bear any fruit.
An aphid infestation can spread and completely take over your plant within a matter of weeks, so it is ideal to check the leaves every few weeks for any early signs.
A popular way to deal with aphid infestation in tomato plants is to spray them with a strong stream of water, such as from a hose. The stream of water will help in knocking the aphids off your tomato plant, eventually drowning them.
Although this method has proven to be quite successful, you should take care when doing so as not to damage the stems or the blossoms of your plant, especially if they have become weak due to the infestation.
Alternatively, if there are only a few bugs on your plant, you can choose to remove them by hand.
Be sure to dispose of and kill them as soon as possible to avoid any spreading to your other plants.
There are also multiple chemical solutions and pesticides on the market for dealing with aphids, particularly handy if you want a quick cure.
Preventing black spots on tomato leaves
The most common mistake that most gardeners make is planting their tomatoes too close.
Ensure that you plant your tomato plants spaced apart to prevent any disease from spreading to your crops.
They should be planted around 18-24 inches apart to prevent the disease from spreading.
Similarly, you shouldn’t plant tomatoes in the same area every year. Rotate them around your garden, to avoid replanting into infected soil.
Diseases can survive on plant debris and soil throughout the winter months, and some even as long as years.
Purchasing disease-resistant seeds is another way to prevent your tomato plant from suffering black leaf spots.
Many varieties of tomatoes have been bred to be immune from certain diseases, such as blight. This information can usually be found on the back of seed packets.
Frequently Asked Questions Relating to Black Spots on Tomato Leaves
Can you eat tomatoes with black spots on them?
It is not recommended to eat any tomato fruits that are discolored, as they could be infected with disease or fungi. Eating diseased fruit could cause you to become unwell.
Can I compost a diseased tomato plant?
Do not compost a tomato plant that has been affected by diseases. Any diseased plants should be disposed of or burnt to avoid spreading this to any other crops.
Marcel runs the place around here. He has a deep passion for houseplants & gardening and is constantly on the lookout for yet another special plant to add to his arsenal of houseplants, succulents & cacti.
Marcel is also the founder of Iseli International Commerce, a sole proprietorship company that publishes a variety of websites and online magazines.