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Potato late blight is the main disease that affects both plants and tubers. Statistics show that about 10-15% of potato crop losses are associated with late blight. Sometimes the yield is reduced to 50%. Experienced summer residents and gardeners know that it is necessary to take measures in time in order to prevent this disease. Protecting potatoes from late blight is very important. What is this disease, and what are the main methods to combat it?
Causes and signs of late blight
The main reason for the development of potato late blight is pathogens – oomycetes (lower fungi). The incubation period of the fungus is 3-16 days, so the disease progresses very quickly. Their mycelia are found in potato seeds previously affected by late blight. Soil and plant debris also serve as one of the main sources of the disease. The probability of potato late blight disease increases with the presence of microorganisms in the seeds and soil. When the stems germinate, the disease in the form of released zoospores rises along with moisture through the soil capillaries, and the tubers become infected from the tops.
The optimal conditions for the development of the disease are a certain temperature regime: + 15-25 degrees Celsius and humidity over 90%, especially with drip-liquid moisture. Potato late blight spreads rapidly with dense planting. Very often, the onset of the development of the disease is observed after heavy dew has fallen. With the onset of heat, fungi slow down their spread. Late blight spots dry up, and new healthy leaves grow, thus rejuvenating the stems. So the heat will help fight the disease.
The main signs of the disease are dark spots on the leaves, which quickly spread throughout the plant. As a result, after a while, brown spots appear on the stem and the tissue dies. If you look at the underside of the leaf, you can see the spores of the fungus in the form of a white coating. The main difficulty is that these harmful spores are easily spread by wind or through water in rainy weather. If you notice the symptoms of potato late blight in time, then there is still a chance to save the crop. Late blight of potatoes in a few days can cause darkening, curling and drying of the leaves. And the potato tubers themselves will become covered with hard spots and become a source of disease for neighboring tubers.
Methods of prevention
There are several methods for the prevention of potato late blight disease: choosing a place for planting, using disease-resistant potato varieties, and treating with special preparations. Let’s consider these methods in more detail.
Earlier it was said that one of the main sources of late blight is the soil. Therefore, you should choose leveled fields for planting potatoes, since it is in depressions (places with higher humidity) that there are foci of the disease. The soil should drain well and not be heavy. The place for a plantation or vegetable garden should be sunny and well ventilated. You also need to increase the distance between planting different nightshade crops to avoid infection. It is worth choosing varieties that are resistant to infection and observing seed shifts. The same crops cannot be grown in the same place for more than 4-6 years. The best predecessors for potatoes will be perennial grasses, winter crops, flax, beets, corn. If this is not possible, then you can sow the area with mustard or radish. These plants need to be mowed down and buried in the soil. It has been proven that the risk of infection with a fungus can actually be reduced by 3 times by alternating potato plantings in 2-3 years.
If you use already infected seed material, then late blight disease is guaranteed. But how to identify infected tubers? To do this, it is advised to warm up the planting potatoes for 10-15 days at a temperature of 15-18 degrees. Under such conditions, you can see the first signs of the disease and discard the diseased seeds. Next, you need to carry out the treatment with some fungicides or drugs, which increase the resistance of potatoes against late blight. Among such funds are noted Immunocytophat, Agat-25K.
Important – when selecting planting material in the fall, you need not to throw away the damaged tubers, but burn them! After that, the seeds must be well dried and sent for storage.
It is worth paying attention to varieties resistant to late blight. Among them are noted: Arina, Verb, Sante, Visa, Lazar, Tomic, Rosara, Oredezhsky and others. The varieties listed are not completely resistant to potato late blight, but they have varying degrees of susceptibility to the disease. There are varieties in which only the stems, or only the tubers, will not be infected. It is important that some mutations may occur that will reduce the resistance of the variety, or new strains of the disease may appear. As you can see, you will not be able to completely protect your crop from late blight disease only by choosing the right potato variety, but in this way you can reduce the rate of development of the disease and delay the time of epiphytosis. There is an option for planting early varieties of potatoes. The disease simply does not have time to completely infect the plant, and the crop will be saved.
Harvesting potatoes should be carried out in sunny weather, as high humidity contributes to the preservation of spores of the late blight fungus. It is important to dry the tubers well and prevent injury.
One of the methods of disease prevention is the application of mineral fertilizers, namely potash and phosphorus. At the beginning of the development of the culture, it is worth increasing the dose of potassium by 2 times, and phosphorus by 1,5. In addition to potash and phosphorus fertilizers, wood ash can be applied as a top dressing. Carefully monitor the application of nitrogenous fertilizers. Excess nitrogen retards tuber development, resulting in greater susceptibility to disease.
In order to contribute to the thickening of the skin of potatoes, it is necessary to loosen the soil and mow the tops. Also for this purpose, the chemical preparation Reglon Super is used.
In dry and cool weather, you can not water the potatoes by sprinkling, but only run a hose into the grooves. If you see diseased plants, they need to be cut and burned. Weeds can also create a favorable microclimate for the development of late blight. They can interfere with the uniform application of fungicides or harbor fungal spores.
Treatment
Potato late blight is an incurable disease, but measures can be taken to prevent the development and spread of the disease. There is a certain scheme for processing potatoes to prevent and combat ailments. The first time it is necessary to carry out the treatment when the tops grow by 25-30 cm. In this case, it is recommended to use systemic preparations or mixtures. With a frequency of 10 days, it is worth spraying the potatoes with a solution of copper sulfate, based on 10 liters of water, 2 grams of vitriol. You can also spray the plants with 1% Bordeaux liquid or a solution of copper sulfate (10 grams per 20 liters of water). Watering with a solution of manganese is allowed.
Already before the potatoes begin to bloom, it is worth carrying out another processing. It is advised to use the drug Epin. If weather and other conditions indicate to you that the risk of the disease is low, then you can apply the protection of potatoes from late blight with resistance inducers: Silk, Krezatsin, Immunocytophat.
After one to two weeks, it is recommended to treat with contact fungicides (for example, copper oxychloride, Efal, Ditan M-45). If spraying is carried out for a preventive purpose, that is, the plants are not infected, the dose of the agent should be halved. It is important to remember that the fungus adapts to systemic fungicides.
If the potato is already infected, then Ridomil Gold MC, Oxyhom, Ridomil MC are used against the fungus. Processing can be carried out no more than twice with an interval of 10-14 days, but only until the flowering period. Bravo is used after the potatoes have faded. Spraying interval 7-10 days. At later stages, in order to fight tubers with the disease, it is allowed to carry out treatment with Alufit. Remember that even with a slight infection of the tops, severe damage to the tubers is possible. Therefore, you should protect the tops with a fungicide until it dies off completely.
It is important to remember that if it rains after treatment, it must be repeated.
The people know very well how to deal with potato late blight. These methods are effective for use at any time of the growing season. It is recommended to spray the plants with a mixture of milk with a few drops of iodine. Good results are brought by the treatment of stems with infusion of arrows and cloves of garlic. To prepare the preparation, garlic must be rubbed in an enameled bowl, poured with water. After 12 hours, it is necessary to strain and you can spray the plants.
It is impossible to completely cure potatoes from late blight disease, but it is necessary to fight it in order to preserve the potato crop.
Video “Late blight and protection against it”
The video tells about a serious potato disease – late blight, about the causes and ways to deal with it.
