Fight against late blight of potatoes

Fight against late blight of potatoes

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The second half of summer is not only a wonderful time when it is already possible to collect the first fruits from cultivated plants, but also the time of awakening of the destructive phytophthora. This insidious disease, affecting mainly nightshade crops, is capable of mowing, if not the entire crop, then most of it. Some gardeners do not try to fight it, but simply choose early varieties of tomatoes, peppers, eggplant and potatoes and harvest before the start of the phytophthora season. Other gardeners are actively, and, most importantly, effectively fighting this scourge. Below, we will talk about ways to combat late blight in potato beds.

What is late blight

Late blight, late blight or brown rot is an extremely common disease of the nightshade culture. To a lesser extent, it can affect strawberries, castor oil plants and buckwheat. It was this disease in the 19th century that caused the great famine in Ireland. And in our country about 4 million tons of potatoes are annually utilized from late blight.

Late blight is translated from Latin as a destroying plant. This disease received this name thanks to its causative agent - the simplest fungus Phytophtora infestans. It multiplies incredibly quickly, devouring up to 70% of the crop in the course of its life. This fungus is spread by zoospores, which can be found in infected soil or potato tubers. Also, phytophthora zoospores may be present in potato storage, if infected tubers have ever been stored there. Zoospores of the fungus that causes late blight spread along with moisture from diseased potato tops to healthy ones. Moreover, the more moisture and the warmer the weather, the faster they spread.

The first signs of the disease will be noticeable on the lower leaves of potato bushes, but then the rest of the tops, along with the underground tubers, are affected. On potato leaves, late blight manifests itself in the form of brown spots with an inconspicuous fluffy white bloom, which is formed by fungal spores. On the stems of potato tops, instead of spots, stripes of dark brown color are formed. However, in humid weather, spots and stripes become wet and rot, which facilitates the spread of new spores. In dry weather, the spots and stripes dry out. Potato tubers affected by late blight also have dark spots, which later begin to grow in depth and width and rot.

Important! Before harvesting potatoes for storage, it is very important to carefully examine the tubers, especially if the potatoes were harvested in late July or early August.

At this time, the signs of late blight on potato tubers are not yet as pronounced as in the autumn harvesting period.

Preventive measures

Before we tell you how to process potatoes before planting against late blight, we will tell you about the preventive measures for this disease. The set of agrotechnical measures proposed below will significantly reduce the likelihood of infection of potatoes with late blight:

  1. Treatment of the soil on a potato bed from late blight and its subsequent mulching.
  2. The choice of tubers as planting material is only those potato varieties that have high resistance to late blight. Among all varieties of potatoes that are resistant to this disease, Vesna, Nevsky, Red Scarlett and Udacha are popular. If potato varieties susceptible to late blight will be used as planting material, then before sowing it is necessary to determine whether they are carriers of spores or not. To do this, potato tubers must be placed for several weeks in a room with a temperature of +15 to +18 degrees. All this time, it is necessary to carefully examine the potato tubers for the presence of darkening, and if they are found, discard the affected tuber. In order to prevent further spread, the remaining tubers must be treated with Fitosporin-M or Agatom-25K.
  3. Compliance with crop rotation in the beds.
  4. Separate planting of nightshade crops in the beds. This measure is necessary to protect different crops from late blight, if one of them is infected.
  5. Compliance with the recommended distance between adjacent potato bushes. Heavily thickened plantings of potatoes are poorly ventilated, as a result of which ideal conditions are created for the spread of phytophthora.
  6. Hilling potatoes. Moreover, the thicker the layer of earth will be at the stem of a potato bush, the less likely it is to develop phytophthora.
  7. Timely removal of all diseased potato bushes with their subsequent burning.

Treatment of potatoes from late blight

Together with preventive measures, pre-sowing treatment of potatoes is almost 100% the key to success in the fight against late blight. Processing potato tubers before planting can be carried out using folk remedies or using chemicals.

Folk remedies

Folk remedies will perfectly help in the prevention of late blight, as well as in its initial stages. But in the event of a large-scale infection, folk remedies will be powerless.

Most often, the following recipes are used in the fight against late blight:

  1. Garlic infusion. To prepare it, you need to finely chop 100 grams of garlic and add 10 liters of water to it. This solution should be infused during the day. Only after that, the ready-made infusion must be filtered and sprayed onto the potatoes. It is necessary to repeat the treatment every week for 30 days. Moreover, each time a new solution must be prepared to process the potatoes.
  2. Infusion of sour kefir. Using fresh kefir in the fight against late blight will not give the desired results, so it is important to take sour kefir. It should be mixed in a volume of 1 liter with 10 liters of water and mixed well. After insisting for 2 - 3 hours, the solution will be ready. With this infusion, potato bushes must be processed every week until the time of harvest.
  3. A very effective method of combating late blight is the use of a solution of copper sulfate, potassium permanganate and boric acid. To prepare it, you need to dissolve a teaspoon of each component in 1 liter of boiling water. After they have cooled down, the resulting 3 liters must be mixed with another 7 liters and the potatoes must be processed. Processing with this solution is carried out twice a season: in July and August with an interval of several weeks.


Chemicals are the most effective means of fighting late blight. But they have one drawback: they can accumulate in tubers and soil. Therefore, the treatment of potatoes with these preparations should be carried out only when other means are powerless and only in the dosages indicated by the manufacturer.

For potatoes, there is one effective scheme for the use of chemicals against late blight. It includes the following steps:

  1. Before planting, it is recommended to treat the tubers with Fitosporin-M.
  2. At this stage, only potato tops are processed from phytophthora. Moreover, its height should be at least 25 - 30 cm. For processing, you can use any drug with a fungicidal effect, for example, Bordeaux liquid, copper sulfate or copper sulfate.
  3. The third treatment of potatoes from late blight should be carried out before flowering. If weather conditions contribute to the spread of late blight, then Exiol, Epin or Oxygumate should be used for treatment. If the weather is warm and dry, then you can limit yourself to drugs such as Krezacin or Silk.
  4. After one to two weeks from the third treatment for late blight, the potatoes must be treated with fungicidal preparations with a contact effect. These drugs include Ditan M-45 and Efal. If the infection becomes large-scale, then these drugs must be replaced with stronger ones, such as Oksikhom and Ridomil. In this case, re-treatment should be carried out after 2 weeks from the first.
  5. After flowering, potato bushes can be treated with Bravo for phytophthora.
  6. At the stage of formation and ripening of tubers, it is recommended to treat potatoes with Alufit.

Important! Processing potatoes with any of these preparations should be carried out only in dry and calm weather.


Processing of potatoes from late blight is carried out until the crop is harvested. In most cases, with the timely start of the fight against potato late blight, it will not be difficult to defeat it. But it is much better to prevent the development of this disease by pre-sowing soil cultivation and careful selection of potato tubers for planting.

We recommend that you watch the video, which will tell you about how to deal with potatoes in case of late blight infection:

Watch the video: Potato Late Blight (December 2022).

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