“I can’t figure out what disease(s) is affecting my ‘Black Krim’ tomato plant (which may have now spread to the ‘Rutgers’).” In late June I noticed significant leaf curl of some vines of the ‘Black Krim’. June was a dry month, so I thought it might be a physical problem. However, watering didn’t seem to help. By early July, rains had returned and the leaf curl did not go away. I then saw healthy lower leaves turn gray-black in just a few days, often starting at the edges of the leaves. Recently, though, I’ve started seeing leaves 18 to 24 inches above ground that have black spots and maybe light gray centers. Petioles have similar elongated grey/black spots and some fruit stems (that produced no fruit) have turned completely black. Some leaf lesions are larger and could be the small spots merging. The main stem is not solid green and shows some grey-black coloration. There seems to be no correlation between the vines that exhibit wilt and the vines that have spots. I removed the wilted vines. Some had small dark markings on the interior of the stem while some looked healthy. So far, the fruit, which is still green, has not shown any spotting or discoloration.
The leaves do not turn yellow and brown, like you see with alternaria and septoria. Plus, it this just doesn’t look like the normal problems I get on my tomato plants every year. I’m thinking Stemphyllium or possibly TSWV (or both?), but neither seems to fit those symptoms entirely. I’ve looked at the lesions under a macroscope and no fruiting bodies of fungi are apparent. Plus, the lesions don’t have any mold-like fuzziness. The wilting and scattered small sores point to TSWV, but the fruit doesn’t have any spots or changes in color (even on infected stems), and the sores on the leaves don’t look like they have circular rings around them.
I’ve been using B. subtillus spray since transplanting, and liquid copper sulfate spray more recently. Neither seems to be having much effect. Trichoderma harzianum strain T-22 was also used on this plant to stop Fusarium wilt, which has been a problem for me in the past. I realize that plants don’t all exhibit the same symptoms to the same diseases every time. It’s also possible that both diseases are at work here. Any thoughts you have here would be greatly appreciated. ” Question from S Saving of Kansas City, Missouri.
Answer: Nothing is worse than experiencing debilitating tomato diseases when all a gardener wants is a successful crop. Diseases are likely to happen unless the gardener grows the disease-resistant tomato hybrids and makes sure the raised beds are well-ventilated and the weather is dry. Fungal and bacterial diseases are especially likely to happen. Since you asked about at least two things at once, I will answer your question in sections. First, I will look at the pictures you sent of leaves and stems that have black spots and sootiness on them.
Seeing the edges of your tomato leaves turning black can be alarming. Healthy tomato foliage should be a vibrant green, so blackening leaves often indicate an underlying issue. While it’s normal for lower older leaves to yellow or drop off blackened edges especially on upper younger leaves warrant attention.
There are several potential causes of black leaf edges on tomatoes. By observing your plants closely and considering all the factors, you can pinpoint the culprit and take action to get your tomatoes back to their beautiful best.
Common Causes of Black Tomato Leaf Edges
Here are the most likely reasons for blackened edges on tomato leaves
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Bacterial diseases – Bacterial speck, bacterial spot and bacterial canker can all cause black lesions and leaf edge necrosis. These bacteria thrive in warm, humid conditions.
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Fungal diseases – Early blight, late blight and Septoria leaf spot fungal diseases create dark black spots on leaves that can merge and blacken leaf edges.
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Environmental stress – Fluctuating moisture levels, extreme temperatures, strong winds or poor nutrition can stress plants, leading to blackened foliage.
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Herbicide damage – Drift from nearby herbicide applications can twist, curl and blacken tomato plant leaves.
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Sunscald – Intense afternoon sun coupled with stressed roots can scorch leaf edges black.
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Natural senescence – Lower leaves naturally turn yellow then black as the plant ages. This is normal for the lowest 1-3 leaves over time.
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Insect pests – Thrips, spider mites and other piercing-sucking insects can damage foliage and cause black spotted leaves. Look closely to detect them.
The most common causes of black leaf edges are bacterial or fungal diseases. To identify the exact problem, closely observe the pattern and progression of the black lesions.
Diagnosing Bacterial Causes
Bacterial tomato diseases display distinct symptoms that can help pinpoint the specific bacteria present:
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Bacterial spot initially creates small black water-soaked spots on younger leaves near the top. Spots merge into large black patches surrounded by yellowing tissue.
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Bacterial speck results in tiny black spots on leaves, no larger than a pinprick. The spots give leaves a speckled appearance.
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Bacterial canker appears first as black edges and tips of leaves. Stems and fruit develop raised black lesions and cracks. Entire leaves turn black and die.
For all bacterial infections, the black spots and patches start small then spread rapidly under warm, moist conditions. Nearby rain, overhead irrigation and high humidity encourage these bacteria to proliferate.
Identifying Fungal Culprits
Several common tomato fungal diseases also manifest as black leaf edges:
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Early blight first appears as dark colored spots on older lower leaves. Concentric rings form in the spots. Eventually the lesions grow together and whole leaves turn black.
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Late blight emerges as dark, water-soaked irregular spots. These tan lesions turn black, appearing greasy or slick. Fuzzy white mold develops under humid conditions.
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Septoria leaf spot creates small circular spots that start gray but become black over time. Eventually the tiny spots merge and blacken larger areas of leaves.
Fungal diseases develop slowly at first then accelerate into severe infections. Examine the patterns and speed of the spots to determine if a fungus is the issue.
Environmental Factors
Even without diseases or pests, tomato leaf edges can turn black due to environmental stresses:
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Moisture fluctuations – Blackened leaf edges may arise after periods of very dry or very wet soil. Keep soil consistently moist but not saturated.
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Temperature extremes – Hot sun followed by cold nights can stress plants. Provide shade and wind protection to fluctuate temperatures gradually.
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Poor nutrition – Insufficient nitrogen causes lower leaves to yellow then turn black. Fertilize tomatoes regularly per package directions.
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Herbicide damage – Nearby spraying can cause twisted blackened leaves almost overnight after exposure to drifting chemicals.
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Sunscald – Intense afternoon sun and heat coupled with stressed roots can blacken leaf margins. Shade plants during hottest part of the day.
Monitor environmental conditions closely to determine if stresses are contributing to your tomatoes’ blackened leaves. Making adjustments to shelter, shade and irrigate plants can help remedy environmental issues.
Typical Patterns of Leaf Blackening
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Bacterial diseases – Black spots start small then rapidly expand in warm, humid weather. Younger top leaves affected first.
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Fungal diseases – Leaf spots emerge slowly then accelerate into severe infections. Lower leaves affected first.
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Environment – Blackening happens in response to specific stresses like drought or herbicide exposure.
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Senescence – Older lowest leaves yellow then blacken over time. Progresses upwards gradually.
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Sunscald – Leaf edges of upper exposed leaves blacken during intense midday sun.
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Pests – Chewing pests make ragged holes. Sucking insects cause silvery speckling then blackening.
Solutions for Black Tomato Leaf Edges
The first step is to accurately diagnose the cause. Once you know why your tomato leaves are blackening, here are potential solutions:
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Improve airflow and reduce watering if fungus is suspected. Remove damaged leaves promptly.
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Add a bactericide like copper spray if bacterial spot, speck or canker are present.
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Check for nearby herbicide use if symptoms appeared suddenly after nearby spraying.
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Provide shade cloth if black edges are caused by sunscald.
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Rule out environmental factors and make adjustments to soil moisture, temperatures, wind protection or fertilizer.
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Monitor for pests like thrips that can be treated with insecticidal soap or neem oil.
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Accept natural lower leaf yellowing and drop. No action needed for normal senescence.
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Remove infected plants immediately if late blight is confirmed to avoid rapid spread.
Preventing Tomato Leaf Blackening
While some fungal diseases will always pose a threat, proper practices can reduce the likelihood and severity of blackened tomato leaves:
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Select disease-resistant tomato varieties when possible.
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Inspect plants carefully before buying at nurseries and reject any with spots.
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Disinfect tools and wash hands between plants when pruning or staking to limit spread.
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Stake or cage tomatoes to keep them off the soil and improve airflow.
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Water at the base of plants using soaker hoses or drip irrigation to minimize foliage moisture.
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Space plants appropriately and prune overgrowth to encourage good airflow.
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Apply mulch or otherwise prevent splashing of soil onto lower leaves during watering.
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Remove suckers and lower leaves touching the ground to reduce disease entry points.
Staying vigilant for symptoms and addressing issues promptly can limit damage, but the best defense is prevention.
When to Worry About Black Tomato Leaves
While an occasional black leaf here and there is no cause for concern, significant blackening of multiple leaves should put you on high alert. When the edges or large sections of leaves rapidly turn black, take immediate action to treat the likely underlying disease or pest issue.
Leaf blackening on just the oldest 1-3 leaves is often natural senescence and requires no intervention. But blackening of younger upper leaves demands prompt attention and treatment to protect your tomato crop.
Don’t panic if you notice a few black edges on older seedling leaves or lower foliage. But significant blackening of multiple leaves should prompt close inspection and diagnosis. Catching and treating tomato problems early increases your chances of still harvesting a bountiful crop.
Black Spots on Tomato Leaves Causes and Solutions
FAQ
What do overwatered tomato leaves look like?
What does tomato blight look like on leaves?
Why do tomato leaves have black edges?
Tomato plant leaves will have black edges if they develop bacterial or fungal infection, especially late blight, Septoria leaf spot, bacterial canker, and bacterial speck diseases. If the disease hasn’t started to spread, you can sometimes stop it from going any further.
Why do tomatoes turn black if left untreated?
The stems will also turn black if left untreated, and the tomato fruits will grow white spots. Often it is the case that bacteria canker has come from an infected tomato seed. This disease spreads rapidly, and just one infected plant could wipe out a whole greenhouse of crops.
How do you stop a tomato plant from turning black?
Spray the solution all over your plant and its leaves, and repeat once a week until you see signs of improvement. One way to prevent tomato leaves from turning black is to choose varieties of tomato plants created to resist disease. For example, some tomato seed packets will state that they are blight resistant.
How do you know if a tomato plant has black spots?
It starts with small black spots that are most often found on the underside of the leaves. In more mature plants, you might also notice a yellow ring around the spots, which can either be sunken in or raised. If left untreated, the skin of your tomatoes will also have black spots on them.
