There are two types of leaf spot disease, bacterial and fungal diseases. Both show similar symptoms, the typical leaf spots. The disease caused by fungi is treatable. In the case of diseases caused by bacteria, there are no remedies approved in the home garden. Home remedies are hardly effective. There is no biological control. Leaf spot disease is usually not very dangerous, but it is a sign that the affected plant is not doing well. Either there are care errors or the location or the plant substrate does not fit. Read what there is to know about leaf spot disease in the following text.

Bacterial leaf spot diseases

The bacterial leaf spot disease is caused by bacteria. These penetrate the leaves through injuries or natural openings and cause the typical leaf spots. There are different bacteria. Various plant species are also attacked. Damp and cool weather favor the infection and the disease spreads faster. Dry and warm weather, on the other hand, can slow down or stop the spread of the disease.


Leaf spots caused by bacteria often have a light yellow edge zone. In contrast to leaf spot disease caused by fungal infections, there are no spore containers.

  • Round or angular necrosis on the leaves
  • Often light yellow edge zone
  • Often a broad, noticeable dark margin around the leaf spots
  • Blattränder vertrocknen


In bacterial leaf spot disease, bacteria are of course the cause. The pathogens are transmitted from leaf to leaf through moisture, either through rain or irrigation water. They can also spread to the foliage from damaged areas of bark.

The leaf spots usually do not pose a threat to the plant, but they are an indication of another, more serious disease.


The most important measure is to remove the infected leaves as quickly as possible. In addition, it should never be poured from above, i.e. not over the leaves.
Chemical control is unfortunately not possible.

Fungal leaf spot disease

The fungal leaf spot disease is caused by fungi, mostly of the genus Alternaria, Ascochyta and Septoria. They attack different plant species and genera. The leaf spots, in the middle of which the actual fungus and its fruiting body are located, are typical. The mushrooms thrive particularly well in wet conditions, in damp weather or in leaves that do not dry well. The mushrooms can then multiply strongly. This allows the spots to merge into one another. Alternatively, holes can appear in the leaves (shotgun disease).


The spots on the leaves can vary depending on the type of fungus and the respective host plant. However, the location and care also have an influence on the damage and the spread of the fungus. The spots are usually yellowish at first, then change to brownish and can also turn black.

  • Round gray or brown spots of necrosis, which often flow together to form large damaged areas
  • The leaves can occasionally die off
  • Chrysanthemums, flame flowers, hydrangeas, peonies, rhododendrons and cherry laurel are often affected
  • Also often infested – houseplants
  • Fruit trees are also affected


There are various fungi that cause the diseases, mostly of the genus Alternaria, Ascochyta and Septoria.
Here, too, the leaf spots do not pose a threat to the plant itself, but indicate another, more serious disease.


Prevention is a very useful measure. Since the fungi spread especially when it is wet, it must be ensured that this is prevented as far as possible. There is little that can be done about the weather, but conditions can be improved. For example, the planting distance is very important. If the plants are too dense, this can result in a lack of light, a lack of nutrients or sunburn. In addition, the leaves do not dry well if there is not enough space. The settlement of mushrooms is favored.

It should also never be poured over the leaves. Additional moisture is always unfavorable.

Tip – The best way to protect your plants is to use resistant plants when you buy them. Even that doesn’t provide 100 percent protection, but it’s a good start. Nevertheless, there are a few things that should be considered.

In the case of infected plants, the affected leaves must be removed as soon as possible. Fallen leaves should be raked together after the growing season. In order to avoid the spread of the disease into the next year, the infected material must be destroyed. Scissors must be disinfected after use in order not to transfer the adhering spores to other plants. Never compost cut material. If plants are infected over a large area, it is better to destroy them.

Biological remedies are not available and home remedies are hardly effective either. There are fungicides against some fungal pathogens: Broad-spectrum fungicides are best used, as in most cases there is more than one fungal pathogen.

Frequently asked questions

Which fungi cause leaf spot disease?

Mainly these are mold and / or hose fungi.

Alternaria (mold)

  • More than 40 species, mostly black fungi
  • Spores survive in the soil, even in winter
  • Are carried onto their host plants by the wind
  • Particularly common in dry, warm weather, interrupted by brief rainfall
  • Tiny, chocolate-brown to black dots on young leaves are typical
  • Sharp demarcation from the green plant tissue
  • Circles grow and merge
  • The rest of the plant can also be attacked

Ascochyta (mushrooms)

  • There are beneficial and harmful as well as fungi
  • Over 2,000 species
  • Prefer rather humid and permanently cool weather
  • Brown, elongated spots, even on very young plants
  • Center light gray, with small, black dots
  • Stems also affected
  • Fungal spores grow out of the tissue crevices (spherical and hemispherical shape)

Can leaf spot disease also infect lawn grasses?

Yes, that is possible. The infestation can be recognized by small, watery, brown spots on the leaves. These can get bigger and bigger up to large patches of mesh. The tip of the leaf becomes yellowish. The disease usually breaks out in spring or autumn. If the root neck or leaf sheath also become diseased, the grass dies. You can combat it by mowing the lawn and completely removing the cuttings. Targeted fertilization, which strengthens the grass, is suitable for prevention.

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