Phytophthora, late blight of potatoes, how to deal with a dangerous disease

It has long been thought that the most dangerous disease of the nightshade, potato including - late blight - is transmitted only with planting material. In the soil in our conditions, the pernicious fungus does not overwinter. However, in recent years, this truth from agro-medical schools seems to have been questioned. Potato late blight acquired new properties and, it seems, went into a counteroffensive. Therefore, it is necessary to fight against phytophthora all the year round.

  • Causative agent of late blight
  • Control measures and prevention of late blight

Phytophthora(Phytophthora - comes from the Greek, literally means "plant destroyer") - parasitic fungi that cause brown rot in plants. Now they are found in 80 species.

Late blight- fungal disease of plants caused by phytophthora.


In Europe, phytophthora was first discovered in 1830 and for ten years covered the whole territory - from 1843 to 1847 a real epidemic broke out here (agronomists say "epiphytoty").

In the 1840s, the aftereffects of late blight reached a catastrophic level in Ireland, where the population was most dependent on this staple food. The result of epiphytoty was the death from hunger of about 1 million. people and emigration from the Netherlands more than 1 million. human. Even today, the Irish population remains less than three-quarters of what was in the early 1840s. These dramatic consequences of the late blight epidemic arose from the lack of chemical and genetic methods to combat this disease.

In our country, the disease of phytophthora is widespread. The greatest harm it does to potato plantations in the north-western part of Russia. The outbreak of late blight is usually associated with rainy weather. But especially quickly the disease devours planting of potatoes, if cool, wet nights alternate with warm wet days. With such a favorable weather for him, the fungus can spread hundreds of kilometers. And since the potato has a long growing season, is susceptible to the disease throughout the summer, then The danger of epiphytoty is preserved always and everywhere, where comfortable conditions for development develop fungus.

Usually, potatoes fall ill in the second half of the vegetation period, when the plants bloom. Affected at the beginning of the leaves from the lower side - there are more stomata. In these natural openings penetrate the thin outgrowths of the hyphae of the fungus. From the moment of infection of the plant to the first symptoms of the disease is only 4 days. At the beginning of the mass flowering below the lower leaves of the plant appear dark brown patches with a grayish coating. Their dimensions are rapidly increasing. Within a few days the tops can turn into a rotting rotting mass.

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Causative agent of late blight

The causative agent is a lower fungus parasitizing on a living plant, capable of developing on the dead plant remains of potatoes or tomatoes. The mushroom hibernates in the form of its vegetative body - mycelium - in infected tubers, plant remains. The motherland of this mushroom is South America, where the potato originated.

Mushroom phytophthora parasitizes most of its life on living tissues of potatoes - leaves, stems, tubers in the form of a mycelium. With sick seed tubers, he quickly passes to shoots, and from them - to potatoes of a new crop. On the peel there are slightly impressed stains of leaden color, irregular shape. Under the skin of this spot, the tuber tissue is first reddish, and then darkens. If the infection is strong, the stain is diluted.

In the soil, the fungus usually does not last long. But this is usually. In recent years, a more aggressive form of phytophthora has appeared, which previously occurred only in Mexico. Now the disease can manifest earlier, before the budding phase - flowering. Its harmfulness has greatly increased. A characteristic sign of late blight of potatoes or tomatoes was the massive damage to the stems. The development of the disease is noted even under conditions previously considered unfavorable for phytophthora. The resistance to fungus of regional potato varieties has significantly decreased.


The increase in the harmfulness of phytophthora is associated with changes in the composition and properties of the pathogen itself. If earlier he had wintered only in the form of a mycelium on tubers, now the sex structures are formed in the affected tissue - the so-called oospores. They can accumulate in the soil, becoming an additional source of infection. Such contaminated soils for many years become unsuitable for planting the nightshade soils.


Of particular danger is the fact that, in addition to potatoes and tomatoes, the causative agent of late blight parasitizes some wild-growing species of the family of nightshade. For example, on a sweetly bitter nightshade. Moreover, such an "intermediate host" strengthens the formation of oospores, it itself serves as an accumulator of infection. The first symptoms of the disease appear now at any stage of growth, the development of plants, starting with seedlings. The first infectious spots are often found on both the upper and lower leaves, either on the stems at the base or at the point of growth. It happens that even young shoots or shoots are already completely infected. They die at once.

The infected tops with oospores of the fungus, falling into the soil, will serve as a permanent source of accumulation of resting structures. They have kept their vitality for several years. After a winter rest period at low temperatures, oospores spring in spring with high soil moisture germinating by infecting healthy potato sprouts. Thus, primary foci of infection are created, giving rise to the development of the next phytophthora population. When tubers are planted in such soil, they also become infected with late blight. The disease can occur at any stage of growth and development of potatoes.

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Control measures and prevention of late blight

Fight with phytophthora should be almost all year round. It's never too late to check, and if necessary, to sort out the seed potatoes, to remove sick, damaged tubers. In time it is necessary to purchase disinfectants, which will be needed for spring pre-plant dressing. This - TMTD - 80 percent wettable powder, polycarbacin, Dita M-45, nitrafen, formalin.

Simultaneously, store mineral fertilizers. Their use makes it possible to reduce the spread of late blight one and a half to two times. I would just like to warn those who, when using mineral fertilizers adhere to the rule of oil, do not spoil the porridge. Alas, the excess in nitrogen soil, not compensated by potassium and phosphorus, facilitates the spread of the disease, markedly reduces the amount of healthy potatoes.

Even beginners gardeners know the high efficiency of phytophthorosis available to everyone - spring germination of tubers for 20-25 days.

It is worth recalling that in the years with especially favorable for the development of phytophthora conditions without the use of a complex of chemical plant protection is indispensable, a good harvest can not be obtained.

On household plots for potato processing, 5% nitrogen is allowed to be used - 10 g of the drug are consumed per 10 liters of water. The term of the last treatment is 20 days before harvest. The maximum four-fold processing is carried out.


Medex (a mixture of copper sulfate with calcined soda ) is used throughout the growing season. The rate of consumption is 100-150 g per 10 liters of water. The last treatment is 15 days before harvest. Four treatments are possible.

Polycarbacin 80 percent takes 40 grams per 10 liters of water, the last treatment - 20 days before the start of harvest. Four-fold processing.

Copper chloride 90% solution (40 g per 10 liters of water) - 20 days before the harvest, five treatments for the growing season.

Arzeride 60% - 50 g, 20 days before the beginning of harvesting, three-fold treatment.


Well, most importantly, where the new form of phytophthora began to rage, it is necessary to abandon the prevalent practice of growing potatoes from year to year in one place, to provide spatial isolation of solanaceous cultures.

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