In warm, humid weather, the risk of infection is particularly high. That doesn’t mean plants are safe from fungus and bacteria in cool, dry weather. Basically, the hobby gardener must never let up in his vigilance, because plant diseases are always lurking to strike. Some spores have even specialized in certain genera. Anyone who acts according to the motto ‘identified danger is averted danger’ will take a good look at the following list of the most common plant diseases. The earlier the first symptoms are diagnosed, the more effective the treatment will be.

fungal and bacterial diseases

  • Grauschimmel (Botrytis cinerea)
  • Powdery mildew (Erysiphaceae)
  • Downy mildew (Peronosporaceae)
  • Fire blight (Erwinia amylovora)
  • Late blight and brown rot or root rot (Phytophthora infestans)
  • Monilia fruit rot and tip drought (Monilia laxa, Monilia fructigena)
  • Leaf spot disease (Alternaria, Ascochyta and Septoria)
  • Fusarium-Which (Fusarium)
  • Verticillium-Welke (Verticillium dahliae und Verticillium albo-atrum)
  • Tree canker (Nectriaceae)
  • Sternrußtau (Diplocarpon rosae)

Grauschimmel (Botrytis cinerea)

This mold has a wide range of prey from more than 230 host plants. It typically settles on dead plant parts and creates a furry-grey covering. Of course, if a plant is weakened by unfavorable cultivation conditions, such as over-fertilization, moisture or standing too close together, the gray mold has no qualms about attacking these plants until they rot and die. The following countermeasures have proven effective:

  • Water moderately and fertilize little.
  • Mulching with straw, brushwood or leaves.
  • Keep leaves and flowers dry.

Powdery mildew (Erysiphaceae)

There is hardly a hobby gardener who has not yet had to endure a confrontation with the ubiquitous sac fungus. In the field, in the greenhouse and indoors, the disease manifests itself as a mealy coating on the upper side of the leaves. In view of the first symptoms, there is an immediate need for action to counteract the spread.

  • Ventilate the greenhouse and room sufficiently.
  • Remove affected plant parts.
  • Spray with a milk-water solution.

Downy mildew (Peronosporaceae)

As an egg fungus, these spores penetrate deeper into the plants and cause a greyish coating on the undersides of the leaves. As a result, yellow-brown spots appear, which spread more and more and endanger the entire plant. Unlike powdery mildew , this fungus prefers a wet environment.

  • When planting, make sure there is enough space between them.
  • Basically do not water over leaves and flowers.
  • Strengthen resistance with copper lime gifts.

Fire blight (Erwinia amylovora)

This notifiable bacterial disease is extremely feared by all gardeners who cultivate pome fruit. Wherever it occurs, it spreads like an epidemic as the bacteria penetrate through wounds in the cell tissue. Flowers and leaves wilt, curl and turn black. So far there has been no rescue. The competent authority sets up a quarantine zone and orders the clearing.

  • As a precaution, always grow resistant fruit varieties.
  • Avoid injuries to leaves, flowers, shoots and fruits.

Late blight and brown rot or root rot (Phytophthora infestans)

If brown, wrinkled spots appear on tomatoes and potatoes in July, spreading from the edge of the leaves to the center, it is probably the widespread fungal infection. If this plant disease is aggravated by cool, damp weather, there is a risk of a complete loss of the harvest. Chemical pesticides are not allowed in the home garden and probably not in the sense of the hobby gardener.

  • Rain-protected cultivation in the greenhouse or under foil.
  • A planting distance of at least half a meter.
  • Do not grow potatoes and tomatoes next to each other.

Monilia fruit rot and tip drought (Monilia laxa, Monilia fructigena)

It is in particular fruit trees that are afflicted by the fungal spores. The damage they cause sounds horrible: rotting fruit covered with white circles, wilted flowers, limp hanging leaves, puny shoot tips. Only courageous action can now save the fruit plant.

  • Remove diseased plant parts completely.
  • Also pick up fruit mummies from the ground.
  • Administer strengthening mineral-organic fertilizer.

Leaf spot disease (Alternaria, Ascochyta and Septoria)

Various species of fungi make garden and house plants difficult to manage by occupying leaves and shoots. Depending on the type of fungus, different colored spots appear. Plants stressed by care mistakes are particularly susceptible. Excessive humidity plays a major role, combined with no or minimal air circulation.

  • Create drier culture conditions.
  • Cut off infected plant parts.
  • Spray permitted fungicides.

Fusarium-Which (Fusarium)

A large number of popular crops are threatened by the sac fungus genus Fusarium in warm temperatures, such as tomatoes, spinach, peas, cucumbers or cabbage. The spores penetrate the supply lines via the roots, clogging them and causing rapid death. If a hobby gardener notices the typical signs of wilting, it is too late to heal the plant. The significant health risks associated with consumption are likely to be particularly dramatic. As a preventive measure, experienced gardeners take the following measures:

  • Consideration of an adequate crop rotation.
  • Targeted cultivation of resistant species.
  • Consistent tillage.

Verticillium-Welke (Verticillium dahliae und Verticillium albo-atrum)

Verticillium wilt operates similarly to Fusarium wilt. The main difference between the two fungal diseases is that the latter is up to mischief at temperatures below 20° Celsius. Thus, cooler weather does not mean a respite for the plagued hobby gardener, because the two plant diseases maliciously simply alternate. Since the Verticillium wilt preferentially affects woody plants, the following preventative measures can be taken:

  • Avoid drought stress by watering regularly.
  • Refrain from applying nitrogen-rich fertilizers.
  • Do not cause injury to the roots.

Tree canker (Nectriaceae)

The name sounds menacing – and rightly so. When a tree suffers injuries, the fungal spores strike and penetrate inside. Of course, it is not actually cancer in the form of uncontrolled cell growth, but a fungal infection. Cuts and frost injuries open the door to pustule fungi, as do autumnal leaf scars after the leaves have fallen. Typical symptoms are the round growths on trunks and branches. Sooner or later, tree canker also causes fruit rot on fruit trees. Since the disease progresses only slowly, a hobby gardener still has the chance to save his wood in this case.

  • Consistent pruning back into healthy wood.
  • Seal any cut immediately with tree wax.
  • Reduce nitrogenous fertilizers to a minimum.

Sternrußtau (Diplocarpon rosae)

This sac fungus infection, also known as black spot disease, is one of the most common plant diseases. Black-brown, dark purple spots spread out on the leaves in a star shape, after which they turn yellow and fall off. Roses in particular are at risk from blackspot. As a result, young shoots are unable to mature before winter and lose their frost hardiness. Direct control is usually not possible. The gardener can do a number of things in advance to prevent an infestation from occurring in the first place.

  • Keep soil nutrient levels high.
  • Dispose of fallen leaves immediately.
  • Put the garlic between the plants.
  • Strengthen repeatedly with field horsetail broth.

Viral diseases

  • Scharka-Virus
  • Apple Mosaic Virus
  • black ring mottle
  • frizz virus
  • cucumber mosaic virus

If the most common plant diseases are highlighted, viral diseases should not go unmentioned. Viruses are much smaller than fungal spores and bacteria. Because they don’t have their own cells, they don’t have a metabolism, so there’s no point in using medicine. Rather, viruses take over the cells of their hosts in order to spread and multiply. In the infected plants, they live in the flow of nutrients, from where they can only be expelled by a strong immune system. Hardly any plant species is spared by viruses, as these parasites are extremely adaptable and are always on the lookout for new hosts.


Among plums, damsons, apricots, peaches and nectarines, it is considered the most important of all, because it caused catastrophic crop failures. Consequently, the Sharka infection is notifiable. Diffuse markings or rings form on the leaves in May and June. Pock-shaped depressions form on the fruit, under which the pulp changes color and acquires a rubbery consistency. Direct control methods are not known. Appropriate defensive measures result from prevention:

  • Lay out close-meshed netting to deter transmitting insects.
  • Propagation only via virus-free rootstocks.
  • Clear and dispose of diseased trees immediately.

Apple Mosaic Virus

Despite the name, this virus is not unique to apples. Rather, the range of host plants includes more than 85 species, such as roses, raspberries or hops. White to yellowish speckles, stunted shoots, stunted fruit and dead areas indicate the apple mosaic virus. Since the disease spreads very slowly, the hobby gardener does not have to sit idly by and accept the damage:

  • Plant tolerant or resistant varieties.
  • Cut out diseased shoots and branches.
  • Do not remove scions from trees that are suspected of being infested.

frizz virus

Strawberry farmers fear the curl virus like the plague because it causes enormous economic damage. Deformed blossoms, ruffled leaves, yellowish, mosaic-shaped structures and a noticeable decrease in the sugar content of the fruit characterize the symptoms of this disease. It is not uncommon for mixed infections to occur, which intensify the extent of the destruction. Here again, the carriers are the aphids and grasshoppers and probably also worms.

  • Use natural enemies of aphids, such as parasitic wasps, lacewings and ladybirds.
  • Make sure the strawberries are getting enough water and nutrients.
  • Apply a soft soap solution regularly until the pests are removed.

black ring mottle

Almost all cabbage varieties are targeted by black ring spot, which is caused by divergent viruses. White cabbage, red cabbage, Brussels sprouts, kohlrabi and cauliflower are covered with patchy lightening, necrotic rings and black depressions. Since aphids are considered to be the main carriers of the plant disease, they should be fought vehemently.

  • Consistently fend off sucking and biting pests.
  • Keep away the beneficiaries of aphids, like the ants.
  • Rigorously counteract leaf bugs.

cucumber mosaic virus

Experts describe it as the most common virus in the home garden. Cucumbers, zucchini, melons, tomatoes, peppers and petunias are among the preferred victims, along with another 80 plant families. In experiments, even 1000 plant genera could be infected. Frighteningly, transmission occurs through a variety of channels, such as contaminated tools, contaminated seeds, soiled gloves and work shoes. The dreaded mosaic appearance, deformed leaves and unappetizing discolored fruits put the gardener on high alert. In view of these mutilations, damage limitation must be practiced.

  • Selectively sort out diseased plants and dispose of them in the household waste.
  • Be meticulous about only working with disinfected tools.
  • Only use certified, virus-free seeds.


If grey, green, red or yellow lichens appear on plants, the hobby gardener is usually concerned. In this case, however, there is no reason for it, because it is a harmless symbiosis of fungi and algae and not a plant disease. They colonize a wide variety of places, which include not only plants, but also rocks, rocks, walls and roofs. They prefer to thrive on the acidic bark of alder, birch and spruce trees without harming them. Attentive hobby gardeners use lichens rather as indicators for a lack of water or a pest infestation. Where they thrive, there is minimal growth – if any – because lichens prefer a calm substrate. Complex control is therefore not necessary.

Plant diseases are the scourge of the ambitious hobby gardener. Above all, fungal and bacterial infections are among the most common problems, closely followed by viruses, which are particularly difficult for crops and ornamental plants. Anyone familiar with the most common plant diseases is not at the mercy of the plague, because a whole arsenal of prophylactic and defensive measures is available.

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