Black spots on tomato leaves are a worrisome sight. These can signal plant deficiencies and diseases but figuring out which one can be tricky if you don’t know what to look for.
In this article, we will tackle all the possible causes for these spots and how you can treat each one. Aside from this, you’ll also learn how to prevent these spots from forming.
9 Causes of Black Spots on Tomato Leaves
Tomato leaves with black spots can be caused by the following:
- Anthracnose (Early Blight)
- Septoria Leaf Spot
- Fusarium Wilt
- Verticillium Wilt
- Alternaria Leaf Spot
- Alternaria Canker
- Bacterial Speck
- Bacterial Spot
- Phytophthora (Late Blight)
Here’s an overview of the various causes, how they affect the leaves, how to treat them, and how to prevent them.
After you’re done going through the summary, we’ll get to each one by one.
| Cause | Symptoms | Fixes |
| Anthracnose (Early Blight) | Small dark spots on the older lower leavesLarger spots with dark brown-black concentric ringsDeformed leavesInfected leaves turning fully brownLeaf shedding | Remove infected plants and dispose of them safelyApply copper fungicides |
| Septoria Leaf Spot | Small water-soaked dots under old leavesCenters of the spots eventually turning gray then tan with dark brown edgesSpots eventually increasing in numbers | Remove infected plants and dispose of them safelyTreat plants with fungicides |
| Fusarium Wilt | Yellowing on one side of the older bottom leavesWilting leavesBrowning leavesLeaf sheddingStunted growthVery little to no fruit production | Remove all infected parts of the plant and dispose of them safely |
| Verticillium Wilt | Yellowing, shriveling lower leavesWilting parts of the plant, or the whole plantDark brown-black spots on leaf tips | Remove all infected parts of the plant and dispose of them safely |
| Alternaria Leaf Spot | Round dark brown-black concentric ringsYellow haloAn occasional crack in the middle of the rings | Apply copper fungicides |
| Alternaria Canker | Pronounced dark brown-black concentric rings on leaves, stems, and fruits | Apply copper fungicides |
| Bacterial Speck | Tiny raised black spots | Remove infected leaves and dispose of safelyUse copper-containing bactericides |
| Bacterial Spot | Black spots more prominently raised and larger | Remove infected leaves and dispose of safelyUse copper-containing bactericides |
| Phytophthora (Late Blight) | Starting out as pale or olive green dots, quickly developing into water-soaked, brown-black spots on leaves and stems | Apply copper-based fungicides |
1. Anthracnose (Early Blight)
What is Anthracnose (early blight)?
A fungus called Colletotrichum graminicola can cause dark spots to form on tomato leaves. If left untreated, this can easily spread all over the plant as well as the nearby crops.
What causes Anthracnose (early blight)?
The spores of the fungus are usually found dormant in the soil. The spores become active in warm moist weather, water splashing from the soil, and insects or pests, among others.
What are the symptoms of Anthracnose (early blight)?
The most common symptoms of Anthracnose (early blight) are:
- Dark irregular spots on leaves, especially the older, lower ones
- Concentric dark rings are visible in more prominent spots
- Misshapened, deformed, curled, or cupped leaves
- Fully infected leaves turn totally brown
- Leaves dropping off the plant, also known as defoliation
How do I treat Anthracnose (early blight)?
There are two phases in treating anthracnose (early blight). These are:
- Pruning the infected parts of the plants or removing them entirely and disposing of them safely
- Applying copper fungicides that are available in most garden centers
How do I prevent Anthracnose (early blight)?
There are several ways to prevent anthracnose (early blight) from developing. Some of the most effective methods are:
- Selecting and growing disease-resistant tomatoes
- Improving the soil texture for better soil drainage
- Spacing tomato plants out properly for sunlight to reach the lower leaves
- Promoting good airflow between tomato plants
- Watering the soil instead of their leaves
- Cleaning and sterilizing gardening tools, equipment, and clothing
- Practicing crop rotation to prevent the spores from attacking the plants
- Applying mulch to the soil to protect plants from spores in the ground
2. Septoria Leaf Spot
What is Septoria leaf spot?
Septoria leaf spot is a fungal infection, caused by Septoria lycopersici, that affects tomato leaves by giving them small, dark spots. This disease usually starts from the lower leaves and will continue to spread upwards until properly treated.
What causes Septoria leaf spot?
Septoria leaf spot can be triggered by the emergence of warm temperatures and high humidity. The spores can live in the ground but become activated upon coming into contact with water.
What are the symptoms of Septoria leaf spot?
The Septoria lycopersici fungus causes the lower older leaves of tomato plants to exhibit small water-soaked spots. These eventually turn dark, increase in numbers, and spread throughout the whole plant.
The spots can occur on all parts of the tomato plant at any stage of development. Left untreated, the fungal disease can easily wreak havoc through the whole garden.
How do I treat Septoria leaf spot?
You can treat Septoria leaf spot in two stages:
- Remove all the infected parts of the plants, or the whole plant itself if it is beyond saving
- Apply fungicides on affected plants and areas as directed on the package
Note: Always keep the infected plants away from your garbage bins or compost piles.
How do I prevent Septoria leaf spot?
Like any other fungal infections, Septoria leaf spot can be prevented in the following ways:
- Cultivating tomato plants that are resistant to pests and diseases
- Improving the quality of the soil to encourage better water drainage
- Giving enough space between tomato plants
- Providing good ventilation and sun penetration through proper spacing and pruning
- Watering the soil instead of overhead watering
- Practicing good garden hygiene by regular cleaning and sterilizing of tools
- Incorporating crop rotation techniques to prevent reinfection
- Mulching on top of the soil near the plants to prevent spore growth and spread
3. Fusarium Wilt
What is Fusarium wilt?
Fusarium wilt comes from the fungus Fusarium oxysporum f. sp. lycopersici. This particular strain has three races that affect several plants in the nightshade family, such as tomatoes, peppers, and eggplants.
What causes Fusarium wilt?
The fungus lies in contaminated soil and can easily spread. Fusarium wilt awakens from dormancy when the temperatures are warm, humidity is high, overwatering is constant, and drainage is poor.
What are the smyptoms of Fusarium wilt?
Fusarium wilt can be identified by the following symptoms:
- Yellow parts of the older leaves at the base of the plant
- Wilted and limp leaves at the bottom parts of the plant
- Dark and brown leaves
- Shedding leaves or defoliation
- Deformed or stunted leaf growth
- Minimal to no fruit development
How do I treat Fusarium wilt?
Unlike other fungal infections, Fusarium wilt cannot be treated with fungicides. The only recourse is to remove all infected plants, dispose of them safely, and take preventive measures.
How do I prevent Fusarium wilt?
Prevention is the only cure when it comes to Fusarium wilt. You will be successful in avoiding this deadly fungal disease by:
- Growing tomatoes that have been proven to be resistant to both pests and diseases
- Making sure that your growing medium has good drainage
- Preventing the excessive application of fertilizers high in nitrogen content
- Refrain from watering your plants from an overhead position
- Practicing regular cleaning and sterilizing of your gardening tools and equipment
- Implementing crop rotation in your cultivation techniques
- Incorporating mulch around your tomato plants to lessen water-borne contamination
4. Verticillium Wilt
What is Verticillium wilt?
Two fungal strains cause Verticillium wilt, the Verticillium dahliae and the Verticillium albo-atrum. These two work together to cause irreversible damage to many plants, including tomatoes.
What causes Verticillium wilt?
Fungal spores can lie dormant in the soil for many years before awakening to infect crops and plants. Verticillium wilt spores are no exception as they become more active during warm seasons with high temperatures, humidity, and constantly wet soils.
What are the symptoms of Verticillium wilt?
Verticillium wilt symptoms can be identified through the following conditions:
- Yellow, shriveled leaves particularly those found in the base of the plants
- Wilted leaves, stems, or even the whole plant
- Spotted leaf tips with dark brown coloring
How do I treat Verticillium wilt?
Unfortunately, there is no treatment available for the Verticillium wilt. The safest option is to quickly remove all infected plants and dispose of them safely to avoid further spread and contamination.
How do I prevent Verticillium wilt?
While Verticillium wilt has no available treatment, it can be easily prevented. Here are some techniques you can use to avoid this terrible tomato disease:
- Cultivating tomato plants that have been bred to resist pests and diseases
- Encourage good soil drainage by improving the texture
- Promoting good airflow by spacing your plants properly
- Avoiding overhead watering
- Regularly cleaning and sterilizing your gardening tools, equipment, and clothing
- Considering long-period crop rotation cycles
- Placing mulch around your tomato plants
5. Alternaria Leaf Spot
What is Alternaria leaf spot?
Alternaria leaf spot in tomato plants is caused by two fungal strains, Alternaria tomatophila and Alternaria solani. These are soil-borne fungi but can also be transmitted through touch, water, and air.
What causes Alternaria leaf spot?
Alternaria leaf spot normally awakens from dormancy when temperatures are warm, humidity is high, and the area is constantly wet. Sometimes the spores can lie dormant for years and suddenly develop when the conditions are favorable.
What are the symptoms of Alternaria leaf spot?
Plants with Alternaria leaf spot can display the following symptoms:
- Round concentric rings in dark brown and black colors
- Yellow edges around the dark spots
- Large spots can have the occasional crack in the middle
How do I treat Alternaria leaf spot?
Alternaria leaf spot can be treated in the following ways:
- Remove all infected parts or plants and dispose of them safely if the damage is extensive
- Apply organic fungicides on the infected plants to keep sprayed fruits edible
How do I prevent Alternaria leaf spot?
Alternaria leaf spot can be prevented if you practice the following gardening protocols:
- Planting tomato varieties that have been proven to resist pests and diseases
- Spacing your plants properly to avoid overcrowding and excess humidity
- Pruning your tomato plants regularly to encourage sun reach and airflow
- Avoiding direct watering on your tomato plants
- Practicing regular cleaning and sterilizing of gardening tools and equipment
- Implementing crop rotation cycles to lower the presence of pathogens
- Mulching to reduce the chance of fungal contamination
6. Alternaria Canker
What is Alternaria canker?
Alternaria canker is caused by the fungal pathogen Alternaria alternata f. sp. lycopersici. The spores first attack the lower stems and can quickly spread into other parts of the plant, including the leaves and fruits.
What causes Alternaria canker?
Alternaria canker becomes activated when the conditions are right, such as warm temperatures, high humidity, and constant rain or watering. They can be carried through contact with soil, water, or air.
What are the symptoms of Alternaria canker?
Alternaria canker displays the following signs in tomato plants:
- Black concentric canker sores on the lower parts of the tomato plant
- These cankers can quickly spread through the plant affecting leaves, stems, and fruits
- Untreated plants eventually die once these black cankers take over the entire plant
How do I treat Alternaria canker?
Alternaria canker can be treated with copper fungicides. However, if the damage is extensive, it is best to remove all the infected plants and dispose of them safely.
How do I prevent Alternaria canker?
You can easily prevent Alternaria canker from attacking your plants through the following gardening techniques:
- Growing pest and disease-resistant tomato plants
- Practicing proper plant spacing to allow adequate airflow
- Pruning regularly to allow sunlight to reach the lower parts of your plants
- Watering the soil instead of watering your tomato plants directly
- Frequently cleaning and sterilizing your gardening equipment, tools, and clothing
- Mulching the area around your plants to reduce water splashes
7. Bacterial Speck
What is bacterial speck?
Bacterial speck in tomato plants is caused by the bacterium Pseudomonas syringae pv. tomato. It typically infiltrates gardens through infected seedlings, transplants, tools, and contact.
What causes bacterial speck?
Bacterial speck thrives in cool temperatures and wet weather. Typically, it starts to activate and develop in temperatures that range from 63 to 75 degrees Fahrenheit.
What are the symptoms of bacterial speck?
Bacterial speck in tomato plants typically exhibit the following signs:
- Dark brown or black lesions on stems, leaves, and fruits
- Yellow tissue around the black lesions
- Dark lesions are typically near leaf margins
How do I treat bacterial speck?
Tomato plants infected with bacterial speck cannot be treated. The following are your best solutions:
- Removing all infected plants immediately to reduce the risk of further contamination
- Applying a copper-based bactericide on all suspected and affected parts
How do I prevent bacterial speck?
Bacterial speck can be easily spread through water, so it is necessary for you to implement the following gardening approaches:
- Removing all infected and contaminated plants and plant parts
- Cleaning and sterilizing your gardening tools, equipment, and even clothing
- Refraining from using sprinklers as they cause further spread. Use drip irrigation systems instead
8. Bacterial Spot
What is bacterial spot?
Bacterial spots look similar to specks except for the following distinctions:
- Young spots are yellow or light green before maturing into black or dark brown spots
- The older black bacterial spots are raised and larger in diameter
- Large bacterial spots may occur on the leaf margins
What causes bacterial spot?
Bacterial spot is the result from the infection of four species of bacteria. These are Xanthomonas euvesicatoria, Xanthomonas gardneri, Xanthomonas vesicatoria, and Xanthomonas perforans.
These bacteria can infiltrate gardens through contaminated seeds, seedlings, and transplants. These infected specimens may or may not show bacterial disease symptoms.
What are the symptoms of bacterial spot?
Bacterial spot on tomatoes can cause the following conditions:
- Leaf and fruit spot marks
- Untreated plants eventually shed their leaves
- Defoliation, or the shedding of leaves, can cause sunburned plants
- Overall decrease in fruit production and yield
How do I treat bacterial spot?
As with bacterial specks, you can treat bacterial spot in the following ways:
Remove infected leaves and dispose of them safely to reduce contamination and spread.
Use copper-containing bactericides to combat all species of the bacteria.
How do I prevent bacterial spot?
Prevent bacterial spot by adhering to the following gardening practices:
- Keeping your tools clean and sterilized before and after all gardening activities
- Using drip irrigation systems instead of sprinklers or overhead water, which can cause further bacterial spread
9. Phytophthora (Late Blight)
What is Phytophthora?
Phytophthora infestans is the water mold pathogen that is the main cause of late blight. It is a fungal infestation that lays dormant in plant debris and soil.
What causes Phytophthora?
Phytophthora infestans spores can be found in contaminated soils, insects, or pests. They can also become active in moist cool temperatures and spread through water splashes and carriers such as transplants, weeds, and diseased debris.
What are the symptoms of Phytophthora?
Late blight has the following symptoms,
- Phytophthora starts out with leaves having pale or olive green spots
- These quickly develop into water-soaked dark spots on the stems and leaves
- The dark spots can be dark brown, dark purple, or black in color
- On the lower sides of the leaves, pale gray or white ring-like growths may appear
How do I treat Phytophthora?
Late blight can be treated in the following manner:
- Completing removal and safe disposal of all infected plants
- Application of copper-based fungicides to prevent spread
How do I prevent Phytophthora?
The risk of late blight in tomato plants can be reduced by practicing the following safe and healthy gardening practices:
- Growing tomato varieties that have been bred to be resistant to late blight
- Improving the soil to create better soil drainage and nutrient content
- Keeping your tomato plants well spaced out to encourage sunlight penetration
- Regularly pruning to encourage good airflow
- Not watering your plants from an overhead position
- Using drip irrigation systems instead to water the soil
- Cleaning and sterilizing all gardening tools, equipment, and clothing before and after use
- Implementing a crop rotation schedule for three to four years to reduce the presence of pathogens
- Mulching around the plants to prevent water splashing
FAQs on black spots on tomato leaves
Fruits with black damaged parts are caused by blossom end rot. They can be eaten as long as the damaged parts are safely removed.
Tomatoes that have been treated with fungicide are not safe to eat. However, those that have copper formulations are deemed safe to eat. Just make sure to wash the fruits well with warm soapy water.
It would be wise to avoid eating them since fungus and bacteria are not visible to the naked eye. However, you can always wash them thoroughly in warm soapy water if you really want to eat them.
Fungal and bacterial diseases spread through contaminated items. These can be tools, equipment, and clothing. They can also be spread through the air and water.
