Leaf spot disease is common in both garden and houseplants. Various pathogens are responsible for the differently shaped and colored leaf spots, which are often difficult to combat.

Leaf spot disease manifests itself in differently colored spots

Table of Contents

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  1. the essentials in brief
  2. pests and pathogens
  3. Fight
  4. Prevent effectively
  5. frequently asked Questions

    6. the essentials in brief

    • Leaf spot disease is mostly caused by harmful fungi.
    • Sometimes, however, bacteria or viruses can also be responsible for the infection.
    • There are no effective home remedies, usually only a strong pruning helps.
    • Careful planting and care is important to prevent the disease.

    pests and pathogens

    Fungi, bacteria or viruses can be responsible for leaf spot disease

    First of all: There is no such thing as “the” leaf spot disease, since the characteristic symptoms are caused by many different pathogens. Fungi are often behind the infection, but bacteria or viruses can also be the cause. The type of pathogen determines the form of treatment, which is why you should look closely at the symptoms and differentiate between them. While fungal leaf spot diseases can usually be controlled quite well, combating bacterial or viral forms is difficult.

    tips

    A first indication of the possible pathogen is the weather at the time of occurrence, since some forms prefer to appear in cool and damp, warm and damp or warm and dry weather. A short rain shower (after the leaves do not dry off quickly enough) or morning dew is often enough for an infection.

    Fungal pathogens

    The possible fungal causes of leaf spot disease come from three different genera of fungi. The following table shows what these are and how to distinguish them from their characteristic symptoms.

    Alternaria (molds / sooty mold) Ascochyta (Sac fungi) Septoria (other species of ascomycetes)
    characteristics occur particularly in dry and warm weather with little precipitation occur mainly in cool and humid weather Infestation mainly occurs at temperatures between 20 and 25 °C
    Infection / mode of transmission Spores overwinter in the soil or in plant debris, are transmitted by wind plant seedlings are already affected Transmission often through infected seeds
    damage picture initially tiny, sharply demarcated dark brown to black dots, gradually becoming larger and merging elongated, brown leaf spots with a greyish center, which is often covered with small dark spots initially yellowish leaf spots that run into each other, from which mushroom spores grow in a spherical shape
    course of the disease as it progresses, tubers and fruits are also infested stems also affected with sunken spots, growth disorders leaf wilt and fall

    Typical for all bacterial forms of leaf spot disease is the formation of fungal growths on the affected areas as well as spore deposits, which are often located on the underside of the leaves.

    tips

    Shotgun disease, which mainly occurs on stone fruit such as plums and cherries, is also a leaf spot disease caused by fungi. It is caused by the fungus Wilsonomyces carpophilus and occurs mainly as a result of a wet spring.

    Bacterial and viral pathogens

    More rarely, bacteria or viruses cause various forms of leaf spot diseases.

    • Viral pathogens: You can recognize a virus infection by the mosaic-like spread of the leaf spots. There are currently no effective antidotes, only a vigorous pruning can save the affected plant.
    • Bacterial pathogens: Often caused by bacteria of the species Pseudomonas or Xanthomonas, which mainly spread when wet (e.g. through incorrect watering over the leaves or in the rain) and use injuries (e.g. caused by a plant cut) as a gateway. No known effective antidotes.

    digression

    Not all leaf spots are caused by pathogens

    However, leaf spots can also be caused by certain animal pests (such as the sucking behavior of aphids, etc.) or by physical or chemical causes such as strong sunlight (sunburn), hailstorms or harsh sprays.

    Combat leaf spot disease

    The affected leaves should be removed immediately

    Since there are no effective home remedies for the various forms of leaf spot diseases, the only thing that helps in the event of an outbreak is basically the pruning shears for all variants.
    • Cut off all affected parts of the plant generously.
    • Use freshly sharpened and disinfected cutting tools for this.
    • Disinfect them carefully after use to prevent the pathogens from being transmitted to healthy plants.
    • Never dispose of the infected clippings in the compost or even leave them as mulch (€239.00).
    • Instead, throw it in the trash or (if permitted) incinerate it.

    In addition, fungal infections can often only be treated with a broad-spectrum fungicide, since in many cases not just one, but different types of fungi have established themselves. Severely affected plants - regardless of the pathogen - sometimes only have to be removed and replaced with healthy plants.

    Prevent effectively

    Since leaf spot diseases can often be so difficult to control, effective prophylaxis is particularly important to prevent infection. These measures will help you:

    • Pay attention to a species-appropriate location with suitable light and soil conditions.
    • Be sure to keep the recommended planting distance.
    • Pay attention to the rules for a healthy mixed and subsequent culture, as not all plants get along with each other.
    • Never pour from above, always pour directly onto the ground.
    • Fertilize moderately and have a soil test carried out regularly.
    • Give preference to organic fertilizers.
    • Strengthen your plants with home-made plant manure made from stinging nettle or field horsetail.

    "You can also prevent infections by using plants that are resistant to leaf spot diseases (certain cucumber varieties, ADR roses, etc.) or disinfecting the seeds with garlic or field horsetail broth."

    frequently asked Questions

    Which plants are most commonly affected by leaf spot diseases?

    In principle, almost all garden and indoor plants can be affected by leaf spot diseases. However, ornamental plants such as peonies, chrysanthemums, hydrangeas, phlox, cherry laurel, rhododendron and ivy, useful plants such as various fruit trees, cucumbers, courgettes, pumpkins and tomatoes or indoor plants such as the popular flamingo flower (anthurium) are particularly at risk.

    My fruit trees are affected by leaf spot disease. Can I still eat the fruit without hesitation?

    Since leaf spot diseases usually only affect the leaves, the fruit should not be diseased - provided the tree or shrub is not too badly affected and the fruit is able to grow and ripen. You can therefore eat apples, pears etc. from diseased trees without hesitation.

    tips

    Leaf spot diseases occur during the entire growth period between April and September, whereby the spores overwinter on the diseased plant, especially in the case of fungal causes, and the diseased plant can become diseased again in warmer temperatures the following year.

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