Tomatoes are delicious and also healthy. Unfortunately, they are also susceptible to diseases. Here is an overview of the most common diseases of tomatoes and pests.
Tomatoes are one of the most popular vegetables in the garden. Unfortunately, there are also plenty of diseases that can affect the plants and greatly reduce the crop yield.
To avoid throwing your valuable harvest in the trash, it is important that you check your plants regularly. The sooner you notice changes, the sooner you can intervene and fight the pests.
Various tomato diseases and pests can become a serious problem when growing tomatoes. Here you will find help if the home-grown fruits suddenly get unsightly spots, the foliage dries up or bugs spread on the plants, including tips for damage limitation, prevention and control.
What tomato diseases are there?
The fruit rot and stem rot
This rot is caused by a fungus that can penetrate the fruit, especially in injured places on the bark. Especially when the weather is humid in summer, the spores of the fungus can spread unhindered, and the wind ensures transfer to other plants.
You can recognize an infestation by black spots on the bark of the tomatoes, on larger plants the area around the stem can also sink in. Gradually, the plant wilts and the leaves turn yellow.
You’d better prevent this disease by regularly rotating fruit and not using seeds from infested tomatoes for further cultivation. You should place the plants in the bed with sufficient distance from each other to ensure adequate aeration. Immediately remove the infested plant parts and dispose of them in the residual waste – never in the compost. It is also important that you thoroughly clean the climbing aids and destroy the strings with which the plants were attached.
The late blight or brown rot
Also caused by a fungus is late blight. In this case, too, spread is favored by warm, humid weather, and the same is true for dew. Especially in August and September, you should regularly check the plants for possible infestation. Once an infestation has occurred, there is usually no way to save the plant.
The disease shows up as grayish-green spots on the leaves, and the discoloration can range to black. If you look at the underside of the leaves, you will see a grayish or white coating. The leaves often curl up as well.
Infestation usually progresses very quickly, with leaf dieback. However, the fruits and stems may also be infested. Brownish spots appear on the tomatoes, the spots are also hardened and slightly sunken. The fruits then shrivel and rot. Even tomatoes that have already been harvested can still rot up to five days later. Toxins form in the fruit, so the tomatoes are inedible.
When growing tomatoes, it is important to leave larger distances between the tomato plants. Only in this way there is good aeration and after rain showers the plants can dry faster. You should always water only the root area.
It would be optimal if you put a small canopy over the bed or decide on a tomato house right away. It is also helpful to apply a layer of mulch, so that moisture also does not reach the plants from below. You can also make a broth from skim milk and spray the tomatoes with it once a week. To do this, add one package of skim milk in two liters of water. Alternatively, a decoction of onion peel can also help.
Early blight (Alternaria solani)
Early blight is also caused by fungi that are spread by wind. The pathogens also persist in the soil and on tomato trellises. The disease often originates from potatoes, so potatoes should never be planted next to tomatoes.
You can recognize the infestation by round, gray-brown spots on the leaves. The infestation progresses from the bottom up. If the infestation is very severe, the leaves will die as it progresses. Later, you will also see spots on the stems, but they are more elongated in shape. The tomatoes become soft and start to rot from the calyx area.
It is important that you always meticulously clean the wooden poles to which the tomatoes are tied at the end of the gardening season. Since moisture also increases the risk of early blight infestation, you should take the same preventive measures as for the other fungal diseases.
Powdery mildew, another fungal disease, occurs in the garden on many plants. Even the tomatoes are not spared from it. It doesn’t even have to be very humid and warm for the spores to spread unhindered.
The infestation shows itself by a white fungal coating on the leaves and their stems. It appears as if they are dusted with flour, hence the name of the disease.
As the disease progresses, the white spots expand and sometimes cover the entire leaf. Later, the leaves turn increasingly brown and then dry up. The tomatoes themselves do not show any symptoms. It must be said that powdery mildew is rather rare in tomatoes. If there is a disease, then often in late summer, so that then combat is no longer necessary. In the trade you can get tomato varieties that are relatively resistant to powdery mildew.
To prevent the spread of the fungal disease, the affected parts of the plant are removed.
If the humidity is very high in summer, an infestation with gray mold can occur. The spores are then transmitted by drafts, but they can also survive in the soil.
Gray-green spots of varying sizes appear on the leaves and stems of tomato plants. Later, you will also see a gray fungal coating on the leaves. If the stem of the plant is heavily infected, the whole plant may die.
As for prevention of all fungal diseases, tomato plants should be kept as dry as possible during the summer. Adequate plant spacing is important for optimal aeration and faster drying after rain. Remove the infested plant parts and dispose of them in the residual waste, never put them in the compost heap. If you have the tomatoes in the greenhouse and there is a constant infestation of gray mold, you should thoroughly clean the entire greenhouse.
Several fungi are responsible for the infestation with the so-called overturning disease. If the humidity is very high and the soil is acidic, the fungus has an easy time of it. Other favorable factors are waterlogging and heavy compaction of the soil.
Above the surface of the soil, you can see dark constrictions on the seedlings. Due to the fact that they do not have sufficient support, they eventually fall over, hence the name of the disease.
For prevention, the growing soil should be mixed with stone meal and sand. You should think about pricking in time and still water the plants with horsetail broth before transplanting. In the beds, the soil should never be too wet, because waterlogging would be extremely unfavorable. For watering is best to use stale rainwater, which should also not be too cold.
Blossom end rot / leaf curl
If tomato plants suffer from a lack of calcium, blossom end rot can occur.
Spots can be seen on the older leaves, while the younger ones become deformed and remain much smaller; they also take on a dark green color. However, you are more likely to recognize the disease on the tomatoes themselves, as they have watery spots on the flower stalks. These become larger over time and turn brown or. Often these spots are also hardened and sink in somewhat.
To prevent the disease, care should be taken to provide the plants with a steady supply of water and nutrients. If infestation has already occurred, you can administer carbonic acid lime.
Corky root rot
Unfortunately, this fungal disease is late to recognize, because it first appears on the roots. Only later do you see wilted leaves at high temperatures, which also remain significantly smaller. The plant grows very slowly, so of course the yields remain correspondingly smaller. Only after harvest time, when you remove the plants, you will see dead roots that are corky and browned. The fungus may well persist in the soil for several years and can thus lead to new infections time and again.
Already at the time of purchase you should pay attention to particularly robust tomato plants, in addition, a regular crop rotation should take place. After the end of the harvest period, the bed should be dug up as deeply as possible and all plant parts carefully removed and disposed of with the residual waste.
Tomato leaf mold
This fungal infection exclusively affects tomatoes grown in greenhouses. If it is very warm and humid there, the fungus finds ideal conditions to spread. Yellow spots can then be seen on the leaves, and green-brown spots appear on the underside of the leaves, which appear to be covered with velvet. The infestation with this fungus is only visible on the leaves, which visibly dry up.
To prevent the disease, proceed as with blight. If an outbreak has already occurred, water the tomato plants only in the morning on sunny days. Also, provide better ventilation in the greenhouse. When watering, make sure that you water only in the area of the roots, the leaves must remain dry. To allow the air to circulate better, you can remove the lower shoots. If the infestation is very severe, you should resort to a fungicide.
Tobacco Mosaic Virus
In this fungal disease, mosaic-like patterns appear on the leaves, and the plant also drops its flowers. There is bronze discoloration on the plant, and the tomatoes have brown spots at the stem end. The spots are bronze in the young fruits, and corked brown areas appear inside the tomatoes.
Once an infestation has occurred, you cannot save the plant. To prevent it from spreading, remove it immediately. Next year, tomatoes should not be planted in the same bed. As a preventive measure, you can then spray them with a decoction of skim milk or onion skins.
What pests occur on tomatoes?
In addition to the wide range of fungal diseases from which tomatoes can suffer, there are also animal attacks that seriously threaten the tomato crop in case of heavy infestation. Besides classic garden pests such as aphids, whitefly and nematodes, there are a few that specialize in tomato plants.
Tomato leaf miner (fly)
Liriomyza bryoniae is the Latin name of the tunnel digger that eats through the inside of tomato leaves. The fly lays its eggs on and under the leaves. The actual pests are the larvae, because they dig the clearly visible intertwined mining tunnels through the leaf tissue of the tomatoes. With a total development time of 32 days from egg to fly, infestation increases rapidly, especially in greenhouses.
To prevent the spread of the tomato leaf miner fly, infested leaves should be removed immediately. Beneficial insects such as the ichneumon wasp help with natural control.
Tomato leafminer (moth)
Much like the tomato leaf miner fly, the tomato leaf miner moth (Tuta absoluta) goes about its business. The inconspicuous nocturnal gray-brown moth with long, backward-curved antennae is only about seven millimeters in size and spends its entire life on the tomato plant. Females lay around 250 eggs on leaves, in flowers and on young fruit. The damage to the tomato plant first occurs in the upper part on the young shoots and is easily visible. Even the fruits are not safe from the larvae of the leaf miner. Secondary infection with fungi and bacteria is often the result of injured fruit casings. Detection and control of the tomato leaf miner moth is accomplished by pheromone traps. Beneficial insects such as predatory bugs and ichneumon wasps can also be used.
The Bright-line brown-eyel, also known as the tomato moth, is an inconspicuous brown moth whose caterpillars are characterized by an enormous appetite for tomatoes and peppers. You can recognize the four-centimeter-long (1.6 in) caterpillars by their greenish-brown coloring with thin yellow stripes on the sides and black warts.
Like the adult moth, the pests are nocturnal and feed through tomato leaves and fruit. Insect nets or enclosed greenhouses protect against the moth as a precaution. If there is a caterpillar infestation, collect the larvae as soon as possible and relocate them to nettles. Pheromone traps and natural neem-based protectants also help against the vegetable owl.
Tomato russet mite
A major tomato pest is the russet mite Aculops lycopersici. Its life cycle lasts barely a week, so the reproduction rate is enormous. Often the mite passes from potatoes to tomatoes. Since an infestation of tomato russet mite becomes visible on the plants very late, control is difficult. Signs of rust mite infestation are yellowing of the leaves and browning of the main shoots. The flower stalks also discolor, young fruits cork, burst open and fall off, the whole plant dies.
The only effective control of tomato russet mite is the disposal of the entire plant.
Physiological damage to tomatoes
Green collar or yellow collar
If tomato fruits do not ripen properly and a green or yellow ring remains around the base of the stem, it may be that the tomatoes have become too hot. In this case, the phenomenon occurs mainly on the outer fruits, which are directly exposed to sunlight. Too much nitrogen or potassium deficiency can also cause green collar. The fruits are edible, but not very presentable.
To remedy this, shade plants over midday in very exposed locations. Do not fertilize too heavily with nitrogen and choose insensitive light-fruit varieties.
Almost every gardener has experienced this: just before the fruit finally ripens, the skin bursts in several places, and with it the dream of a flawless tomato harvest. Burst fruit on an otherwise vital plant is not a disease but also the result of an uneven water supply. If tomatoes are suddenly watered heavily after a dry period, they literally swell up and eventually burst out of their skins. Water the tomatoes evenly.
When the leaves of the tomato curl upwards like spoons, it is a sign of overfertilization. The phenomenon is also known as leaf curling. Too much nutrient supply or drought stress is usually the trigger and can be easily remedied with consistent watering and slow-acting organic fertilizer.