Potato late blight is a dangerous fungal disease that is difficult to treat due to the ability of the pathogen to develop resistance to fungicides. Farmers focus their main efforts in the fight against late blight on preventive measures, including pre-planting treatment of potatoes, selection of varieties resistant to the fungus, and spraying with copper-containing preparations.
Late blight - what kind of disease is it, what affects
Late blight is a collective concept for many fungal diseases, the causative agents of which are mycelial organisms, lower fungi. In the process of their development, they adapt to a parasitic lifestyle and exhibit pathogenic properties on numerous plants - grass, trees, and shrubs.
Nightshade mushrooms are most often affected by fungi - potatoes, tomatoes, eggplants. But it is not uncommon for signs of the disease to appear on peppers, onions, strawberries, and cabbage. And you can even notice signs of disease on horseradish. The symptoms of the disease are the same in all cultures, but the disease is called differently in different cultures. For example, cucumbers, onions and cabbage have downy mildew, grapes have black spot or mildew, and potatoes have gray rot.
Causes of late blight
Late blight on potatoes is caused by mycelial organisms oomycetes from the genus Phytophthora. Unlike fungi, their cell wall is not made of chitin, but of cellulose. In terms of physiology, they are closer to plants than to fungi, which is why late blight, which causes plant diseases, is placed in a separate taxonomic group.
The microorganism parasitizes nightshade plants (potatoes, tomatoes, eggplants), but can also infect other plants. It reproduces by zoospores that are stable in the external environment. Phytophthora quietly overwinters in the ground even in extreme frosts. Zoospores are well preserved on the soil surface, in last year's tops, tubers, and even on bags or dirty tools, so they are advised to be disinfected after harvesting.
In spring, when the temperature rises above 10°C, zoospores germinate. This is also facilitated by high humidity in the region of 75-90%. It is not without reason that late blight is detected on potatoes especially often in rainy years. Late blight often appears on potatoes planted in swampy fields and lowlands.
Infection occurs in different ways. If you use diseased planting material, the fungus will spread first to the roots, and then to the stem and leaves; young tubers are immediately affected. The same mechanism of spread of the disease when soil is contaminated. Late blight is transmitted to potatoes through the air and infects the tops. Then the spores are washed away by rain, they fall into the ground and infect the lower part of the plant. If the disease is detected in time and the plant is treated, the tubers will remain healthy.
Potato blight - signs, what it looks like, photo of leaves
Since today we will talk specifically about late blight on potatoes, we will talk about the signs of the disease and how exactly to fight the infection on this main vegetable of our table.
The source of the disease is a mycelium with phytospores that lives in the soil. For its further life and reproduction, certain conditions are necessary. Frequent drizzling rains, alternating with sunny weather in the middle of the day, cool nights and heavy dew - this is what is needed for its rapid growth. With the help of the wind and some insects (midges), mycelial spores from the diseased plant are transferred to other bushes.
Signs of disease on potatoes already begin at the beginning of the season and appear during the summer depending on weather conditions:
- air temperature and humidity,
- variety resistance to late blight,
- degree of soil contamination.
In wet, rainy summers, affected plants can be seen in mid-summer; in dry summers, closer to autumn.
First, small dark brown spots appear on the stems and leaves of infected plants, which very quickly increase in size.
Sometimes you can notice a gray coating on the affected leaves - these are spores.
Gradually the leaves turn black, the stems dry out and die.
If no measures are taken, the pathogenic process goes back into the soil, affecting the tubers there. At best, they do not gain weight and lose their consumer properties. Otherwise, they begin to rot in the ground.
Sections of diseased potatoes show areas of affected tissue. Such a vegetable is no longer suitable for food, and during storage it begins to quickly rot and rotten neighboring tubers.
Signs of late blight
According to the description, the incubation period of potato late blight lasts 3-16 days. At first, the disease goes unnoticed, especially when the tubers are initially affected, then brown spots appear on the tops. A white coating is noticeable on the bottom of the leaves, which looks like a thin cobweb. This is the mycelium of the mushroom. After the first symptoms appear, the disease progresses rapidly. The tops wither and dry out for several days.
If you dig up tubers from the soil under an infected bush, you will notice brown spots that unevenly cover the surface of the potato. The cut shows how the fungus penetrates deep into the tuber, brown paths go from the surface to the center, then the potato begins to rot. By the time the harvest comes, there may be nothing left under the bushes.
Affected tubers also deteriorate during storage. After just a few weeks, the entire stock turns into a rotten mass.
Why is late blight dangerous for potatoes and humans?
The main danger of the disease lies in its rapid spread; it multiplies exponentially. Spore forms (oospores) are quite tenacious; they have a dense shell and therefore easily tolerate low and high temperatures. And they do not die in the soil for 3-4 years, or even longer.
In the 20th century, late blight became more active with warming above +8 degrees, almost dying out at +24 and above. The disease of the 21st century is harmful in a wider temperature range - from +3 to + 27 degrees.
Once in a favorable environment (moderate temperature and humidity), oospores germinate into conidia, which are easily spread by wind and rain to neighboring plants, affecting increasingly large areas on the site. In warm moisture, conidia quickly germinate into motile zoospores, which penetrate into plant tissue and begin to parasitize there, gradually destroying them. As a result, the leaves turn black and the nutrition of the entire plant, including the nascent tubers, is disrupted.
Late blight on potatoes is an entry point for various rots on other plants. Tomatoes and eggplants suffer the most. Trying to save the harvest, gardeners have to use various chemicals, which leads to their accumulation in vegetables. Eating vegetables with such additives is unlikely to provide any health benefits.
Methods of soil disinfection
It is impossible to completely defeat late blight, but in order to maximally protect the area from the disease, it is necessary to deprive the pathogen of comfortable conditions for feeding and reproduction. Therefore, before cultivating the soil after late blight of potatoes, all tops and rotten tubers are removed from the garden where it grew.
Especially carefully it is necessary to clean the beds where diseased plants were noticed from plant debris. In small areas, such places are marked with pegs. The collected tops are burned. Sometimes there is advice to bury stems and tubers infected with late blight deeply, but the hole will turn into a time bomb. In a nutrient medium, pathogenic microorganisms multiply quickly, and if the pit is accidentally opened, an epidemic may occur.
Treatment of potatoes for late blight - preparations for treatment in open ground
With late blight, the disease begins from the lower leaves. And if you have already noticed the first brown spots and yellowing of the lower leaves, immediately begin processing the plants.
It is important to spray the plants, thoroughly irrigating the lower leaves and stem, and the upper leaves, of course.
How can you treat potatoes? There are contact and systemic fungicides. Contact ones are cheaper, but if you use them in a rainy summer, you will have to carry out at least 6 treatments. One or two light rains or one heavy downpour will bring all efforts to naught. Therefore, it is better to use system ones, they are more expensive, but reliable. Systemic fungicides can be used from Bayer Consento and Infinito.
Consento
The drug activates plant growth, protects them from various infections and has a therapeutic effect. It is used both for the prevention and treatment of diseases at various stages of development. Among its advantages:
- effective at different stages of disease development and at all stages of plant growth;
- gives a quick and long-lasting effect;
- minimal likelihood of the pathogen becoming accustomed to the product;
- does not wash off during watering and rain for a long time.
Infinito
A systemic fungicide containing the active ingredients fluopicolide and propamocarb hydrochloride. After fluopicolide enters the plant, the agent penetrates into the tissue through the intercellular spaces and causes the death of motile zoospores and further development of the mycelium. And propamocarb hydrochloride acts as a growth stimulant. The protective effect of the drug lasts up to two weeks, depending on the degree of infection and weather conditions. In addition, the remedy
- has a short-term toxic effect,
- non-toxic for birds, bees, earthworms, and water inhabitants;
- increases potato yield.
Quadris
Swiss made product. The active ingredient is azoxystrobin. It destroys the fungus and prevents it from spreading. It has a wide spectrum of action and has a detrimental effect on all mushrooms with the exception of beneficial ones. Besides,
- does not have a detrimental effect on the environment, does not accumulate in leaves and, accordingly, in fruits;
- safe for beneficial soil microflora and its inhabitants;
- does not prevent other biological products from increasing soil fertility;
- Most of the drug after treatment remains in the form of an indelible film, that is, it is both a contact and a systemic drug.
Energodar-Ukravit
The latest Ukrainian-made fungicide with growth-stimulating properties to protect vegetable and melon crops from a complex of dangerous diseases. The active ingredient is propamocarb hydrochloride and fosetyl aluminum. They are used when it is too late to carry out any preventive measures.
Advantages of the drug:
- It has a positive effect on strengthening the plant’s immunity and stimulates its growth;
- Does not cause pathogens to become addictive to the drug;
- Provides protection to untreated plant parts and new growth;
- Convenient to use throughout the growing season.
When using drugs for the prevention and treatment of late blight on potatoes, carefully read the instructions before use. Use protective equipment when processing.
Biological preparations to combat late blight
Biological products are considered environmentally friendly and safe. They contain beneficial bacteria that destroy fungus. They awaken immediately after contact with water, when the drug is dissolved to spray potatoes.
The most popular biological products:
- "Fitosporin-M";
- "Baikal-EM";
- "Late blight."
Biological drugs do not treat heavily infested potatoes. They are recommended for use for prevention or at an early stage of infection.
Important! The integrated use of biological and chemical preparations reduces pesticide stress in plants.
How to get rid of late blight on potatoes
Fitosporin
An excellent remedy for the prevention of late blight. Spraying of plants begins in mid-May, when the plants reach a height of no more than 20 cm. Keep in mind that the peak of the disease begins in mid-June, and when the first signs appear, it is too late to treat with phytosporin.
First, a mother liquor is made from the paste. Do not make mistakes when preparing the solution. A working solution is prepared from the mother liquor. For this, 2 tbsp. l. The mother solution is diluted in 10 liters of water and sprayed. Preventive spraying is carried out in the phase of closing the rows. Repeated treatment is carried out after 7-10 days. Repeated treatment must be carried out, since living phytosporin bacteria need to occupy the entire soil space and begin to fight late blight.
Apply the treatment when there are no weeds under the plants. Otherwise, part of the product will end up on the weeds and not on the plant.
Copper sulfate
Before flowering, treatment is carried out with a 1% solution of copper sulfate (2 tablespoons per 10 liters of water, but no more!). For prevention, spray once. If the disease has already appeared, treat 2-3 times per season. Spraying is stopped 2 weeks before harvest. On tops sprinkled with copper sulfate, conidia cannot germinate and infect other potatoes.
Bordeaux mixture
Phytophthora lives in soils poor in copper. Therefore, during the first hilling, you can do a preventive spraying with Bordeaux mixture, which also contains copper, which inhibits the growth of late blight. It is more difficult to wash off in the rain and protects the potatoes for a week.
The second treatment is carried out when the first signs of the disease appear, the next, third, a week later.
Adhesives (liquid soap) can be added when there is frequent rainfall. In dry weather, do without them, or add 1-2 drops of liquid soap per 10 liters of water.
Potato planting site
Sometimes the microclimate of an area is such that cold air stagnates longer and high humidity persists. This may be a lowland or an area surrounded by forest, which is less ventilated after rain. In such conditions, fungal diseases thrive! But sometimes the reason is different.
This summer the weather has been a real challenge. And not only the skills of gardeners, but also different varieties. Where resistant varieties were planted, the plants suffered less from the disease. And it looks as if “the disease has passed in a stripe.”
Folk remedies for late blight on potatoes
The use of whey with iodine in the fight against late blight has been well proven. The solution is prepared as follows. 2 liters of whey (preferably fermented in a warm place) + 20 drops of iodine tincture and dilute everything to 10 liters of water. You can process not only potatoes, but also tomatoes, eggplants, cucumbers, etc. Spray once a week. If it rains and the temperature drops, spray more often - every 4 days.
Treatment is carried out early in the morning and late in the evening so that it is not hot. So that 0.5-1 hour on the plants before the heat, the solution does not dry out and penetrates inside the leaf and begins its action.
3rd treatment – yeast feeding. For 10 liters take 100 g of pressed yeast or 50-60 g of dry. To activate the process, the yeast is first diluted in a small amount of warm water with the addition of 1-2 tbsp. l. Sahara. After 1-2 hours, the starter is poured into warm water and the working solution for feeding is ready. Yeasts inhibit the growth of pathogenic fungi and act as a growth stimulator. Fertilizing with yeast is carried out once every 10 days, if it is hot, in the rains - every 4 days. To carry out fertilizing over large areas, fine sprayers are used.
What potato tubers should I plant?
What tubers did you plant? Modern potato varieties are bred to be highly resistant to diseases. But gardeners often grow old varieties and plant them for many years in a row. It is known that potatoes degenerate over the years. Even in a normal summer he will get sick.
In addition, they do not take special seed material, but those tubers that remain after winter. Such potatoes have low resistance and are primarily susceptible to late blight.
What tubers did you plant: varietal ones or those that were not eaten over the winter? They say “the miser pays twice.” Spend your money, buy a good variety, and the harvest will be higher! On the same land, with the same labor input, you will get more potatoes!
Prevention of late blight and what to do with potato tops
To protect potatoes from late blight, it is important to carry out timely preventive measures at different stages of cultivation until harvesting. It is better to prevent the disease in the initial stages than to spend more time and money on treatment later.
- Late blight appears in the second half of summer, so now many gardeners prefer early varieties. Such varieties just have time to ripen before its appearance.
- It is necessary to hill up potatoes 2-3 times per season. This is done not only to create adventitious roots and improve plant nutrition. The fact is that high hilling prevents the plants from closing and this can prevent infection of neighboring bushes. And also water accumulates in the depressions between the rows, thereby moisture accumulates at the roots, but not on the leaves of the plants.
- When planting potatoes, do not thicken the plantings. Leave enough space between rows for good ventilation. When plantings are dense, conditions for the proliferation of late blight are preserved. The optimal width between rows is at least 70 cm, and in some cases more. This technique will help avoid infection during rainy summers.
- During the flowering period, you should not feed with organic fertilizers, since organic matter can also give impetus to the development of late blight.
- 2 weeks before harvesting, the tops are cut off so that zoospores from the tops do not transfer to the tubers. All tops are removed from the site or it is better to burn them. In addition, this technique makes the tuber skin thicker, so the potatoes will be better stored in winter.
- Maintain crop rotation. If possible, swap vegetable crops, including potatoes. It is advisable to replant vegetables in this place only after 3-4 years. If this is not possible, choose seed material that is resistant to late blight.
Dear readers, here are the few remedies for the prevention and treatment of late blight. Maybe you know some other means and methods, then write about them in the comments. I will be grateful to you.
Have a good harvest!
Prevention of late blight
1. Well-limed soils are a favorable environment for the development of late blight. Therefore, you should not get carried away with liming. If a lot of lime has accumulated in the soil, you need to restore the natural balance of the soil: add peat and pour coarse sand into the furrows.
2. Fungi prefer a moist environment, therefore it is important to water the plants in moderation and not allow the plantings to become thicker. Water potatoes and tomatoes in the morning so that most of the moisture has been absorbed into the soil by the end of the day. And when growing tomatoes in a greenhouse, be sure to ventilate it.
In addition, humidity often increases during sudden temperature changes (for example, at the end of summer, when it is still hot during the day and the nights are already cold).
At this time, plantings in open ground should be covered with spunbond overnight. First of all, this concerns tomatoes, since not only late blight, but the cold itself can destroy them.
3. Plants with weak immunity are susceptible to any infection. Therefore, make sure that your tomatoes and potatoes receive enough essential microelements (iodine, manganese, copper, potassium and phosphorus). Then garden crops will have less chance of getting late blight.
And to strengthen the immunity of plants, you need to observe crop rotation. So, good predecessors for potatoes are cucumber, zucchini, pumpkin, squash, cabbage, legumes, root vegetables, onions, and for tomatoes – white and cauliflower, cucumber, zucchini, pumpkin, legumes, onions, root vegetables.
4. The development of late blight can be prevented by growing varieties and hybrids that are resistant to fungal diseases. Choose high-quality planting material - and you will not need drugs against late blight.
What factors contribute to the appearance of late blight?
Fungal pathogens are active at high soil moisture. Phytophthora usually develops in the soil in the summer, when an abundance of dew falls on the ground in the morning. The air temperature should be within 15 oC. For this reason, the fungus most often spreads in August. After all, it is during this period that the air in the morning becomes cooler and there is an abundance of precipitation.
How to cure the soil from late blight in the fall? The difficulty of combating the disease lies in the lack of universal solutions. However, there are several methods that make it possible to eliminate the problem. We'll talk about the most effective methods below.
Greenhouse treatment
I will not focus on cleaning the greenhouse - this is a well-known truth. I simply wash my greenhouses with water twice (in autumn and spring), fortunately I have a mini-wash for this.
Disinfection
In the spring, I disinfect the greenhouse using a sprayer - I generously and thoroughly spray all the parts of the greenhouse. I searched and chose how to do this for a very long time! I wanted to disinfect it well and not harm either the greenhouse parts or the soil.
In one of the sources I came across advice to use the product to disinfect premises in medical institutions. I started studying. Liquids like Alaminol were no longer needed due to their aggressiveness towards the environment. As it turned out, all such products contain chlorine in one form or another, which didn’t really suit me, but I didn’t really have a choice. I settled on the veterinary drug Glutex. Apart from the chlorine content, everything suited me: the concentration is very low (5 ml per 1 liter of water), does not harm people and animals, does not need to be washed off, is active against bacteria, viruses and fungi.
I used it to treat greenhouses for three springs, until I saw a video on one of the channels about using chlorine-free bleach for this purpose. After that I breathed a sigh of relief, because... chlorine, even in small quantities, really bothered me.
Last spring I used Bos chlorine-free bleach. You need to dilute it according to the instructions for washing, as a rule, it is 50 g (2.5 tbsp) per bucket of water. Why this particular method? These bleaches are made from perborates. Once in the soil, the product is actively decomposed by soil bacteria without harming them and, as a bonus, enriches the soil with boron. The only limitation: the air temperature must be at least 5°C. Well, the polycarbonate will need to be washed, because... divorces remain. This is a great and inexpensive way!
Perborates are not very aggressive oxidizing agents that perfectly disinfect all treated surfaces, but do not damage the metal and plastic structures of the greenhouse.
Planting green manure
Without chemicals or other solutions, the earth can be completely cleansed with the help of plants. We do not cultivate the land, but sow green manure. What should you sow?
Buy oilseed radish or white mustard seeds. It is necessary to sow in August and early autumn. Before the onset of cold weather, the seeds must sprout and form a root system.
It is in the roots that value lies. In mustard and radish, the root system contains phytoncides, which create a barrier to the proliferation of pathogenic flora. In such an environment, late blight spores die.
Before planting cultivated plants, the roots of green manure are left in the ground: they are cut with a flat cutter or dug up without removing them. During the process of decay, they improve the structure of the soil and enrich it with useful substances.
Green manure saturates the soil with nutrients and phytoncides, which prevent late blight from developing
Disease-resistant potato varieties
Which varieties are better? When different varieties of potatoes grow on a field, the difference is clearly visible: some varieties are more resistant to diseases, others less so. This is primarily noticeable in the leaves. On some bushes they turn black early, on others much later.
The catalogs indicate disease resistance. But everything needs to be checked under specific conditions. Much depends on the soil and microclimate of the site.
On my site, I noticed that the following varieties remained green longer: Laura, Impala, Sandrine, Safiya, Bellarosa, Estrella, Eurostarch, Sudarushka, Manifesto, Yugana, Madeline, Sarovsky.
conclusions
Green manure for late blight on potatoes is an excellent way to prevent and treat fungal infections. But it is better to use it in parallel with fungicides and copper preparations, since a deficiency of microelements is often the cause of fungal damage.
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