Potato blight, also known as late blight or late blight, is a very common disease in potatoes. It is caused by the harmful fungus Phytophthora infestans, which occurs primarily in damp and rather cool weather. This is how you can prevent or fight an infection.

If the leaves of the potatoes warp, it is often too late

Table of Contents

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  1. the essentials in brief
  2. causes and distribution
  3. damage picture
  4. Combat potato blight
  5. Effectively prevent potato blight
  6. frequently asked Questions

    7. the essentials in brief

    • The disease occurs not only in potatoes, but also in tomatoes and other nightshade plants.
    • It is caused by the harmful fungus Phytophthora infestans and occurs primarily after damp weather.
    • The dreaded tuber blight does not necessarily occur together with late blight, since only the above-ground parts of the plant can be affected.
    • Choose the most resistant potato varieties possible for a crop, with early potatoes generally being less susceptible.

    causes and distribution

    When the weather is warm and humid, potatoes are mainly infected by the dreaded late blight (also called potato blight, even if the disease does not only affect potatoes) between the beginning of July and the end of August - and until late autumn. The disease usually only occurs in connection with rain, in dry weather there is usually no danger. The causative agent of this fungal disease is the harmful fungus Phytophthora infestans, which is usually transmitted by wind, unclean garden tools, infected seeds or poor hygiene. It sticks to the moist leaves and can penetrate into the plant more easily on these surfaces because they are swollen and soft.

    Phytophthora infestans often overwinters in potatoes left on the field or stored, which in turn - used as seed potatoes in the following year - represent a renewed source of infection. The fungal spores form at temperatures of around 16 °C and damp weather lasting more than ten hours. They are then transmitted by the wind, for example to neighboring plants. Incidentally, the fungus can also survive in the ground after its spores have infiltrated there with the rainwater. For this reason, a permanently damp substrate can also lead to an outbreak of the disease.

    damage picture

    Potato blight is first seen when the leaves curl up

    "A single infected seed potato is enough to destroy the harvest of an entire acreage."

    Infection with potato blight shows the following symptoms:

    • Yellowing of the leaves at the onset of infection
    • then formation of gray or brown leaf spots
    • Formation of white-grey fungal growth on the underside of the leaves
    • All of the potato haulm dies off within a few days
    • Tuber infestation does not always occur at the same time as late blight
    • Affected tubers have grey, sunken spots
    • Browning of the tubers under the skin

    The insidious thing about blight is that infected potatoes look healthy for a long time and only begin to rot after prolonged storage. For this reason, you should not set up earth heaps and the like near the cultivated areas, and no tubers should be left on the field after harvest.

    Combat potato blight

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    If the potato blight has affected the plants, cut off the leaves immediately and discard them. Never throw the affected plant parts on the compost, as fungal spores can remain there for a very long time. In the next year, these may then cause a new infection. It is better to dispose of the leaves with the residual waste. After the leaves have been removed, the tubers can remain in the ground for at least three weeks until the shell has hardened.

    digression

    Plant potatoes in a different spot each year

    Since the fungal spores in the soil and in plant residues survive for a very long time, you should change the areas under cultivation for nightshade plants such as tomatoes and potatoes every year. This is especially true if an infection has already occurred in the previous year. Plant marigolds in the bed instead, as they clean the soil.

    Effectively prevent potato blight

    If possible, the potato cabbage should not be wetted when watering

    However, the most important measure to combat potato blight is effective prevention. The following tips will help you contain the disease:

    • Be sure to keep the recommended planting distances and do not plant the potatoes too close together.
    • Don't plant potatoes and tomatoes (and other nightshades) in close proximity to each other.
    • Change the area under cultivation every year and keep to the crop rotation.
    • Never pour from above, always pour directly onto the ground.
    • If possible, water early in the morning so that the moisture can dry off quickly afterwards.
    • Watering in the evening, on the other hand, promotes fungal infestation.
    • Fertilize moderately and especially avoid over-fertilizing with nitrogen.
    • Support the plants' defense system with home-made plant manure (e.g. horsetail or garlic tea) and rock flour.(14.13€)

    By the way, the pre-germination of the tubers, which you can position in shallow bowls or egg cartons in a bright and frost-free place in early spring, also has a good preventative effect against potato blight. Under the influence of light, short, green sprouts sprout from the eyes of the tubers after just a few weeks. This pre-germination gives the plants a head start in growth so that they mature earlier and infestation with the fungal disease can be prevented at an early stage.

    digression

    These potato varieties are resistant to potato blight

    There are no varieties that are really resistant to potato blight due to the diversity of the pathogen. Instead, however, you can use disease-tolerant or disease-resistant varieties that are less likely to become infected. This applies above all to potatoes of the varieties 'Annabelle', 'Bettina', 'Caprice', 'Donella', 'Granola', 'Lolita' and 'Mariola', but also to some commercial varieties in particular.

    frequently asked Questions

    Can you still eat tubers infected with potato blight?

    Potatoes affected by blight should not be eaten

    Since the fungus Phytophthora infestans, which causes the disease, produces carcinogenic toxins during its metabolism, it is not advisable to use even slightly infected potato tubers. Even cutting out brownish areas is of no use in this case, as invisible fungal threads still run through the potatoes. Therefore, remove and dispose of infested bulbs and do not eat. They should not be fed to animals either.

    Are potato blight and late blight of tomatoes the same disease?

    In fact, tomato late blight and potato blight are caused by the same fungal pathogen, Phytophthora infestans. It's the same disease, so don't grow nightshade plants in close proximity to each other or in a row in the same bed.

    tip The mounding of the potatoes also protects them from rotting to a certain extent. This step is best done in early summer.

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Vegetable garden