“My succulent house plants have dry leaves in the middle of the stem and black spots. Why is this happening?” Question from Karina of Wenatchee, Washington
Answer: Succulent plants can develop dry leaves when they are being either overwatered or underwatered. The black spots and the fact that leaves are drying and dying in the center of the stem indicates stem and root rot, which is caused by a fungal infection that develops when plants are being overwatered. (Click here for some great images of overwatered succulents.) Sadly, central spotting and leaf death is an indication that your plant is dying and will not recover.
“I have a St.Theresa grapevine that has grown and produced very well. After being devastated by Japanese beetles last year, it developed several distorted leaves. Is it possible the Japanese beetles gave it some virus or disease? I cut it way back. Now, this spring, it has been making a comeback. But I noticed yesterday that some of the leaves at the ends of the new growth look distorted and discolored again. They look like the pictures of Eutypa Dieback. Help! What do I do?” Sharon of Colorado
Answer: Japanese Beetles (Popillia japonica) have been reported to vector some bean viruses, but there is no report or research to support that they spread any diseases of grape (Vitis vinifera). What is more likely is that your vines were weakened by the damage, left more prone to infection, and they obtained a disease. Other grape pests, such as mites, also spread grape diseases and they could have been the vestors. Either way, there are several grape diseases that can cause leaf distortion and discoloration. Here are some possible foliar grape diseases along with identification tips and management suggestions.
Grape Foliar Diseases That Cause Distortion
Grape Anthracnose (Elsinoe ampelina, fungal) causes symptoms on both leaves and fruit. Foliage will appear spotted and have brown lesions that cause leaves to curl. The grapes also develop dark lesions. Apply a Bordeaux mixture spray or Liquid Copper Fungicide to infected vines when they are dormant.
Eutypa dieback (Eutypa lata, fungal disease): Leaves can appear stunted, curled, and cupped. It is easily identified by cutting a stem: infected wood will have a wedge of darker, discolored wood against healthy, lighter wood. It infects older vines that are over five years of age. There is no known cure, so infected vines must be removed.
Getting outside help is my ultimate recommendation. The best way to firmly identify your grape disease is to send a sample to your local extension agent and have it tested in a lab. (Please click here to search for your local extension agent!) Definitive results are necessary because you do not want to destroy your grape if it has a curable disease.
“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.)
“We live in South Florida (Miami). My daughter-in-law has planted an aloe plant in the ground. It’s growing nicely but has black spots on it. Should she be concerned?” Question from Brenda of Miami, Florida
Answer: Florida rains are too much for succulent Aloe (Aloe vera). It is a dryland plant from the Arabian Peninsula that is best suited for cultivation in Southern California and the American Southwest in the US. It requires dry, fast-draining soil, once established. Too much moisture stresses aloes and invites fungal disease. Black spots on the leaves are due to fungal disease, but there are several things you can do to stop its spread.
To grow aloe well where you live, it should be potted. Before potting up your aloe, remove the worst of the infected leaves; just cut them off. Choose a pot big enough to accommodate its root system that has drainage holes at the bottom. Your aloe will need very fast-draining soil, such as Black Gold Cactus Mix. When you are ready to transplant, dig the aloe from the soil, remove the excess soil from its roots, and plant it in the pot with fresh mix. Finally, water it in lightly, and once its foliage is dry, spray it with a natural & organic, copper-based fungicide (click here for an example).
Place your potted aloe in a sunny to partially sunny spot under an eave or covered patio where it will not get rain. This will allow you to water it as needed. I recommend watering no more than twice a month, and water it from the base while being sure to keep its foliage dry.