Brown to black spots on tomato fruit and leaves are not always a reason to abandon the tomato crop. Infested plants can usually be treated easily.
Table of Contents
Show all- the essentials in brief
- Brown spots on tomato fruits
- Brown spots on tomato leaves
- FAQ
- Brown spots on tomato fruit can be an indication of blossom end rot, late blight, or early blight.
- In contrast to late blight, late blight and early blight, blossom end rot is due to a lack of nutrients.
- Tomato leaves with brown spots can also indicate early blight.
- At the same time, bacterial wilt and leaf spot disease can cause brown spots on the leaves.
the essentials in brief
Brown spots on tomato fruits
It is not uncommon for amateur gardeners to be frightened by brown spots on tomato fruits. The rotten spots can be an indication of serious diseases that sometimes result in a whole crop failure. Some diseases weaken the plants so much that they die before the first harvest.
Blossom end rot, late blight or early blight?
It is already written in the Bible: “You will recognize them by their fruit.” Because if you look closely at the tomatoes themselves, you can tell exactly what disease the plant is suffering from. Blossom end rot forms brown spots at the base of the former flower base, while early blight mainly affects the upper areas. By contrast, late blight and brown blight generally form large brown spots.
blossom end rot
Blossom end rot is easy to recognize and easy to distinguish from other diseases. It is more likely to occur in new planting sites and inexperienced hobby gardeners than in experienced tomato professionals. Because blossom end rot is not a bacterium, but an undersupply of the important plant nutrient calcium. If the interplay of watering, fertilizing and pH of the soil is the same, there will usually be no symptoms of deficiency.
Causes. Neither fungi nor bacteria are causes of blossom end rot. Instead, the plant lacks the mineral calcium, which is responsible for the structure and stability of the cell walls in the tomato fruit. If there is a lack of the important nutrient, then the cell walls collapse.
Symptom. Small, dark spots at the bottom of the fruit appear at the beginning of a deficiency. These spots grow larger and watery-glassy and can take up the entire bottom half of the tomato. The damage picture is completed by a cupping of the end of the flower, which becomes leathery and rotten. Both ripe and unripe fruits can be affected.
Prevention. To avoid blossom end rot, the soil should be adequately supplied with calcium. Organic fertilization from compost and manure is sufficient in most cases. The use of nitrogen should not be overdone. The ideal pH value of the soil is 6.5 to 7. Rock dust can make the soil more basic if the value is too acidic and at the same time provide calcium.
Late blight and late blight
Late blight (Phytophthora infestans) is a fungal disease that usually originates from infected potato plants. Damp and cool summer months favor the proliferation of fungal spores. While tomatoes grown outdoors are more frequently affected, greenhouse tomatoes suffer less often from late blight due to the better climatic conditions.
Causes. The fungus is found in almost every soil and especially on potato tubers intended for planting. Phytophthora infestans therefore spreads through the soil around the potato and can thus reach the lower leaves of the tomato through spray water when watering. There the fungus enters the plant and multiplies rapidly.
Symptom. At the beginning of an infection, the leaves and stems are covered with gray-green spots that are blurred. After some time, these change from brown to black. A white fluff often forms on the underside of the leaf. Even the stem can have brown-black spots. The fruits get brown, concave rotten spots, which are mainly found on the upper half of the tomato. The flesh has hardened under the rotten spots.
Prevention. First and foremost, tomatoes should be planted at a sufficient distance (60-70 cm) from each other and as far away from potatoes as possible. In addition, to prevent the rapid multiplication of the fungus, dryness and ventilation should be provided. Regular exhaustion and a rain cover are ideal for this. Disinfect buckets and climbing aids with boiling water after each season so that no spores are carried over into the following year.
early blight
Another fungus that affects tomatoes in the home garden is Alternaria solani or Alternaria alternata. Like most sac fungi, the early blight pathogen likes a humid climate; but in contrast to late blight, warm temperatures. The fungus or its spores are naturally found in the soil and survive long periods of fallow.
Causes. Alternaria infects tomato plants either via the soil by spraying water or via the roots, via trellises or directly via the tomato seeds. Incorrect watering or insufficient fertilization weaken the plant and make it more susceptible to infection. Humid and warm climates favor the multiplication of the fungus considerably.
Symptom. The leaves of an affected plant show grey-brown spots with a yellowish edge. The patches, which are also dry, occur in an irregular manner and become larger. At the same time, slightly differently colored rings form in the spots. Over time, the leaves curl up and eventually fall off. The early bloom disease makes itself felt on the fruits by brown-black spots at the base of the fruit stalk. The spots are slightly curved inwards, rather hard and show a similar ring structure.
Prevention. Seeds from affected plants should not be used for rearing next year as they are already infected. Here, too, the motto applies: prevent splashing water on the leaves. Good ventilation helps the dew dry. Climbing aids and buckets must be thoroughly cleaned after each season. A field horsetail extract can be sprayed on the leaves as a boost or added to the irrigation water.
Brown spots on tomato leaves
Brown spots also often show up on other parts of the plant: early blight, leaf spot and bacterial wilt cause brown spots on tomato leaves. Deficiency symptoms can also lie behind leaf discolouration. As a rule, leaves with conspicuous spots should be removed to be on the safe side.
Deficiency symptoms in tomato plants
An imbalance in nutrients can be a cause of brown spots on the leaves. A nitrogen deficiency first manifests itself on the lower leaves, where they first turn yellow and then brown. If there is a potassium deficiency, the edges of the leaves turn brown and dry up. Light brown spots that extend to the entire leaf and only allow the leaf veins to shimmer green indicate a magnesium deficiency.
The shape and the limitation of the spots are decisive for a precise determination of the cause
early blight
Brown spots on tomato leaves can be an indication of the fungal early blight. A detailed description of the causes and symptoms as well as tips for prevention can be found in the paragraph above.
leaf spot disease
In general, if the tomato plants are in the immediate vicinity of the celery, this indicates an infection with the leaf spot pathogen. The Septoria fungus specializes in root vegetables, but may also attack tomatoes. Therefore, celery - like the potato - should be planted far away from the fruiting vegetable.
Causes. As with most tomato fungal diseases, infection occurs via soil and splashing water or through already infected seed. Persistent moisture in the air and on the plant parts drives the development and reproduction of the fungus. Compared to the other diseases mentioned, leaf spot disease is rather rare.
Symptom. Starting from the lower leaves, the damage caused by the fungal infestation is shown by watery stains that are dark brown in color. The spot is surrounded by a yellow ring. After some time the leaf dies. A closer look reveals spore receptacles (black dots) on the underside of the leaves. The growth of the plant is sometimes severely restricted, which is consequently reflected in a reduced yield.
Prevention. Above all, healthy seed and sufficient distance to celery plants prevent leaf spot disease. Means and a rain roof improve ventilation and protect against persistent moisture, so that fungal growth is inhibited. Clever pouring methods such as an Olla prevent contaminated splash water. A treatment with field horsetail can also strengthen the tomato and help to combat it.
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Brown spots on the leaves can also be an indication of a bacterial infection. The pathogen has with "Clavibacter michiganensis Smith ssp. michiganensis (Smith) Davies et al.” not only has an absurdly long scientific name, but primarily endangers the entire tomato crop.
Causes. The bacterium enters the plant via injuries to the epidermis, but also via stomata. The pathogen feels most comfortable on young plants and at high temperatures between 26 and 28 °C. Contaminated seeds and tubers are the main ways of spreading the bacterial wilt pathogen. Splashing water can transmit the disease to nearby plants. The bacterium can survive for at least a year on inanimate objects.
Symptom. Brown spots appear between the veins on the leaves, which are more reminiscent of burns from a magnifying glass than of rot. Then the undersides of the leaves turn yellow and the ducts of the shoots become brownish and deformed. If left unchecked, the leaves will turn brown and die.
Prevention. In order to avoid infection with the bacteria, the gardener should take care to keep the soil as loose as possible and to plow the soil well and deeply before and after the tomato season. Otherwise, the spray-free watering, squeezing out and sufficient fertilization apply again so that the plant stays strong.
FAQ
Are tomatoes with brown spots still edible?
As a rule, tomatoes with brown rotten spots should no longer be eaten. Late blight, late blight, early blight and bacterial wilt make the fruit inedible. When it comes to blossom end rot, the experts are unsure. It can only be consumed without hesitation if the brown spots are caused by leaf spot disease.
Can infested tomatoes or leaves go in the compost?
Plants and fruits that develop brown spots due to blossom end rot can be composted. All other causes are either bacterial or fungal and must be incinerated or disposed of in the general waste. Otherwise, the pathogens survive and multiply in the compost.
What Causes Brown Spots on Tomatoes?
Brown spots on tomatoes can be due to a calcium deficiency. Bacteria or fungi are often to blame for the brown rotten spots.
What can be done about brown spots on tomatoes?
It is best to immediately remove the tomatoes that have brown spots. This prevents the disease from spreading. Then the cause of the stains must be investigated in detail in order to take effective countermeasures.