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Why Are My Tomatoes Wilting and Showing Black Spots?

By: Jessie Keith

Why Are My Tomatoes Wilting and Showing Black Spots?

“I’m having trouble identifying the disease(s) that is affecting my ‘Black Krim’ tomato plant (and now may have possibly 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 physiological, but watering did not seem to help.  By early July, rains had returned and the leaf curl did not go away.  I then started seeing healthy lower leaves turning grey-black in just days, often starting at the outside edge of the leaves.  Most recently, however, I’ve starting seeing leaves covered in black spots with possibly light-grey centers (these are leaves 18-24” above ground).  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 scattered small lesions and the wilting point towards TSWV, but no spotting/discoloration of the fruit is apparent (even on infected stems) and the leaf lesions don’t seem to show circular rings.

I’ve been using B. subtillus spray since transplanting, and liquid copper sulfate spray more recently.  Neither seems to be having much effect.  This plant was also treated with Trichoderma harzianum strain T-22 to prevent Fusarium wilt (a problem I’ve had in previous years). 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. Unless a gardener plants the most disease-resistant tomato hybrids and has the most aerated raised beds and dry weather, diseases are to be anticipated–especially those of the fungal and bacterial flavor. You’re asking about at least two at once, so I will piece away at your question in an orderly fashion, starting with the photos that you shared of leaves and stems showing signs of black spotting and sootiness.

Black Spots on Tomato Leaves

When black spots like these do not cause leaves to turn yellow and die (or senesce) it usually indicates a surface mold rather than a systemic one. Your spots do not appear to be caused by grey leaf spot of tomato (Stemphylium spp.) or tomato spotted wilt virus (TSWV). Bacterial speck was another pathogen that I considered, but the small, black spots caused by this disease should have a yellow halo. The specks also do not tend to form clusters on leaves like yours.

It looks more like a light infection of sooty mold or related surface fungi. Sooty mold tends to take hold in the presence of sucking insects and the honeydew they produce. Have you observed any aphids, leafhoppers, whiteflies, mites, or the like, on your tomatoes? Even a small population can encourage sooty mold. Moreover, the fruiting bodies can be difficult to see with so little of the disease on leaves, even under a macroscope. Spraying and dry weather conditions will also discourage the development of fruiting bodies and mold spread.

Sooty mold is easily treated. Mix one teaspoon of gentle detergent to 1 gallon of warm water. Dip a clean cloth or sponge into the mixture and wipe down infected leaves and stems. The black mold should come off. Let me know if this is what you observe.

Tomato Leaf Curl

Without seeing a photo, it is difficult to determine what could have caused the significant leaf curl, wilt, and death on your tomatoes. It is certainly not tomato yellow leaf curl virus (TYLCV) because this disease causes leaves to turn yellow and contort over a longer period of time. Herbicide damage and dramatic temperature changes can cause leaf curling and fast necrosis. Herbicide damage is the most common cause. It can appear on old or new growth, depending on what tissues came in contact with an herbicide (click here to see an image of glyphosate drift on tomato.) Broad mites (Polyphagotarsonemus latus) are sucking insects that can cause leaf curl and death of tomato foliage when populations are high. The sucking insects also create honeydew, which can encourage sooty mold.

To determine whether mites are present, do the white paper test. Take a clean piece of white paper, hold it beneath the leaves, then tap the leaves onto the paper. If you have mites, lots of tiny specs will fall, and eventually, they will start crawling around. These are spider mites. Spraying the tops and bottoms of leaves with insecticidal soap and wiping them down will remove spider mites quickly. Multiple applications will be required.

Disease Resistant Tomatoes

Just for future reference, here are some tasty tomatoes with excellent disease resistance. They may not have the allure of unique heirlooms like ‘Black Krim’, but they are tough and tasty.

‘Galahad’ (F3, GLS, LB, N, TSWV): The new, 2020 All-America Selections Winner ‘Galahad’ is a big, red, slicing tomato with excellent flavor that resists five diseases!

‘Granadero’ (F2, PM, TMV, V, N, TSWV): Sauce tomato lovers should try this super disease-resistant paste tomato with uniform, red, well-flavored fruits. It is also an AAS award winner.

‘Mountain Merit (F3, LB, N, TSWV, V): Lots of large, red tomatoes with good, sweet flavor are produced on this compact bush tomato.

‘Toronjina’ (F2, LM, TMV): Highly disease-resistant plants produce lots of sweet and tart, orange cherry tomatoes on shorter indeterminate vines.

Sakura(F2, LM, TMV, N): Red cherry tomatoes are produced early and in abundance on this long-vined, highly disease-resistant tomato.

Please follow up! I would like to know if any of these potential assessments are correct. For a more definitive analysis, send some of your diseased leaves to your local extension agent. (Click here to learn more.)

I hope that your remaining tomatoes produce well.

Happy Gardening,

Jessie Keith

Black Gold Horticulturist

About Jessie Keith


Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.

2 Comments

  1. lrondrunkard

    Thanks for the response. I should have mentioned that a black spot will exist on both sides of the leaf. Under the scope, more developed spots show a grey depression in the middle and I am now seeing a hole form in the middle of the oldest spots. The spotting is also starting to appear on the neighboring Husky Red Cherry (no leaf yellowing, and so far, no indication that the plant is being harmed). The same spotting has also appeared on the Rutgers, but there, leaves with spots have a general yellowing and eventual browning, unlike the Black Krim where the leaves just turn grey/black. On all plants, some of the spots are larger and irregular and are appearing on the petioles and fruit stems, as well as the leaves.

    I’m seeing no sign of mites or aphids. and herbicide damage seems unlikely given where these plants are located and that this plant is between (and intertwined) with two other tomatoes that have shown no wilting. One interesting thing to note is that no new vines have wilted in the past few weeks. Severe leaf curl still exists on some older leaves of the non-wilted vines but whatever caused the wilt seems to be on pause. I’m suspecting that, even though the plants were treated with Trichoderma harzianum, the wilt may have been Fusarium that wasn’t able to fully kill the plant. The treatment only promises “resistance” not immunity.

    The leaf curl may have just been a result of the very dry conditions in June. But I’m still at a loss for what is causing the spotting. Is it simply Alternaria? B. subtillis and copper sulfate treatments seem to be having little effect, though, and they are supposed to work.

    As for getting the plants tested, I can’t find any places that test for diseases. The Johnson Co, KS extension doesn’t indicate they do it, nor does the Jackson Co. MO extension where I live. For plant matter, they only seem to test nutrient contents.

  2. Jessie Keith

    Are you certain that the black spots on your tomato leaves and stems are pathogenic? It is quite moist at the base of your tomatoes. Have you observed any bird’s nest or artillery fungus? When they release their spores, they move far appearing as black spots that attach to everything. It is a fungus that survives on decaying wood, often on bark mulch, so you would not see any fruiting bodies on your tomatoes. It’s just one more possibility. As far as your wilt, it certainly could have been fusarium wilt. I hesitate to give a definitive answer without seeing the damage. Of course, a test would be the only true decider. Fusarium wilt (Fusarium oxysporum sp. lycopersici) is the most common tomato wilt. At its first signs, older leaves wilt, turn yellow, then brown, and then fall. The stunted plants will eventually die. To beat it, look for resistant varieties, discard diseased plant material, and rotate on a three-year cycle. Verticillium wilt (Verticillium albo–atrum) is less common than fusarium wilt and typically seen late in the season when soils are cooler, so it is less likely to be your pathogen. Its first symptoms are v-shaped blotches on the lower leaves, followed by browning veins and blotches. Symptoms then spread upwards, causing wilting and leaf damage. If you were to cut into the stem, the internal veins would be brown and discolored from the ground up to 12 inches. Treat it as you would fusarium wilt. I’d keep looking for a potential testing source. Sun Gro Horticulture (www.sungro.com) tests, but they usually serve large greenhouses. Best, Jessie

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