Potato diseases bring a lot of trouble to potato growers. Photos, descriptions and treatment of scab (rhizoctoniosis), dry rot are the subject of our conversation. After all, potatoes are a staple food in many countries. It is easy to grow in the garden, which makes it popular among gardeners. But potatoes are susceptible to many diseases. The main pathogens are various fungi, bacteria, viruses. Prevention is almost the only means of protection. Many diseases can be prevented if taken in time preventive measures or treatment started at the initial stage.
Scab or rhizoctonia is a common potato disease.
Photo of healthy potatoes and those infected with black scab (right)Description of the disease
Rhizoctoniosis is one of the most common fungal diseases of potatoes. personal plots, called black leg or black scab. It causes especially great damage under conditions favorable for the development of pathogens.
Photo of a stem infected with blackleg Rhizoctoniosis - manifests itself in the form of black scab, rotting of eyes, sprouts, death of roots, as well as “black leg” of stems in wet weather. At the beginning of the development of the disease, lesions on stolons, roots, and stems are reddish-brown. When they mature, they turn into rough, cracked sores. If the cankers are significant, they can encircle the stem, interfering with the normal movement of juices and carbohydrates throughout the plant. Thus, the symptoms of the disease can be seen on the above-ground part and on the tuber.
Sunken brown cankers of varying sizes and shapes can be seen on infected stolons or stems above or below the soil surface. These ulcers can be girdling in nature - in this case the plant dies sooner or later. Young nodules cannot nucleate or develop on such stolons.
Black plaque is the most noticeable sign of the disease. During this phase of the disease, the fungus Rhizoctonia Solani produces dark brown to black growths, as if potatoes were stained in the soil. But this is not the earth, these are the so-called sclerotia located on the surface. They irregular shape, ranging from small flat spots to large raised spots. Although these structures fit tightly to the surface of the tuber, they do not penetrate inside and do not spoil the taste of the potato.
However, if such potatoes are used as seed material, then the sclerotia will inhibit the development of the planted potatoes and may even destroy them. This happens because during the growing season the fungus Rhizoctonia Solani infects root system, the base of plant stems. The movement of nutrients from the leaves to the young tubers is disrupted. The upper leaves curl along the main vein. It appears that they are infested with aphids.
The main source of infection is seed material. Sometimes heavily infected potatoes are not even able to form stems. This symptom is called "no top" and can be confused with the same symptoms as growing from physiologically old seeds.
How to fight, how to protect the crop
Treatment of rhizoctoniasis, black scab requires integrated approach, knowledge of each stage of the disease. One of the most important means of combating the disease is the acquisition and planting of seed material only high quality, which is not infected with pathogenic fungi.
An effective way to combat diseases is prevention - pre-sowing light germination of tubers. The application of rotted manure, superphosphate, and potassium fertilizers reduces the negative effect of the pathogen.
Potatoes are best planted after corn, beets, beans, and peas. Most susceptible to disease weak plants, but it practically does not affect the sprouts of sprouted tubers. Therefore, it is very important to germinate potatoes before planting, so that potatoes infected with rhizoctonia can be discarded before planting. It is equally important to loosen the soil after rain to prevent a crust from forming. In this case, for the mushroom, disease-causing, favorable conditions are not created.
Treatment of potatoes before planting with a 1.5% solution boric acid also protects it from infection with rhizoctonia. The volume of solution should be prepared at the rate of 50 ml per 1 kg of tubers.
The disease is most severe during cold and wet seasons. Microspores persist in potatoes or plant residues for up to two years. When cutting seed material if there are infected tubers among it, for example, when growing potatoes from eyes, infection of healthy ones is possible. Therefore, do not forget to remove diseased bushes from your area. Cut off the tops before digging up the crop so that rhizoctonia bacteria do not have time to get from the leaves to the tubers. Be sure to germinate the seed material in order to remove diseased potatoes in time. Be sure to warm the seed material in the sun, dry it, and green it before putting it away for storage.
Dry rot
Dry rot Description of the disease
Dry rot is caused by several species of fungi of the genus Fusarium, hence the name fusarium dry rot. If, while periodically inspecting the potatoes in the basement, you find dry, depressed spots on the skin, this indicates that they are affected by Fusarium dry rot. These spots are the first symptoms of the disease. As a rule, they appear on the surface of the tuber. Gradually, the pulp under the stain dries out and becomes rotten. At the same time, the skin wrinkles and breaks. In the resulting voids, mycelium grows, that is, mycelium with ripening spores.
Section of a tuber with dry rot Several species of Fusarium fungi cause dry rot. Depending on the species, the spores look like grayish-white, yellowish or pink convex pads.
Where could this potato disease come from? This can be told by the location of the spots.
If dry rot appears on the tubers only at the stolon end (a small indentation on the potato where the stolon was attached), then all the soil in your garden is contaminated with this fungus. Let us explain: a stolon is a lateral underground shoot, at the end of which a potato tuber ripens. This is the potato “umbilical cord” through which the growing tuber receives nutrients from the bush.
And if the potatoes are affected with different sides, then the reason is improper cleaning and poor storage. Most often, the disease begins to rage where there were injuries, cuts, late blight or scab.
Your basement may be too warm. At elevated temperature storage dry rot quickly develops and spreads. As is known, optimal temperature storing potatoes – 1-3 degrees above zero.
Control and prevention measures
Most methods for controlling this potato disease are aimed at preventing injury to tubers during harvesting or storage. Preventing damage to the surface of the potatoes will greatly help prevent infection.
If the soil on your site is contaminated, you should not plant potatoes there for at least five or six years. Green manure or grain crops sown in such a field will eliminate the fungus from the ground, but this may take several years. Therefore, the main thing is to prevent soil contamination. And this can only be achieved by careful selection of seed material.
Is it possible to eat contaminated potatoes?
Is it possible to eat potatoes infected with scab? Or should they be thrown away? Not at all. Select them, remove the damaged parts. Feel free to fry potatoes or make mashed potatoes for dinner.
On the contrary, it is not recommended to eat potatoes affected by dry rot. Even if you have a tuber affected only on one side, you should not eat the supposedly healthy other half. Throw away the entire tuber without any mercy.
To keep your potatoes healthy, select or buy high-quality seed material for planting. Pay attention to the characteristics of the variety, resistance to a particular disease. Dig up potatoes intended for future planting earlier than for food and storage, since the longer they are in the ground, the greater the likelihood of infection. Try to maintain crop rotation.
Sometimes potatoes give gardeners surprises in the form of rotten tubers in the spring, when their stocks are sorted out before planting. Rotten potatoes smell disgusting and cause nearby vegetables to rot. How to prevent spoilage of tubers and keep seed material intact? To answer this question, you need to understand the reasons for potato rotting.
Causes of rotting
How to deal with rot
Rules for storing potatoes
Conclusion
Causes of rotting
Why do potatoes rot immediately after harvesting, why do they start to rot only towards the end of storage? The answer is simple - rot is caused different types infections.
Most often, the development of rot is caused by bacterial infections:
- ring rot appears on potatoes when the first flowers appear.
The disease affects tubers, stems, leaves and stolons. When the tuber is cut, rot is visible, which is located around the circumference. The disease is widespread and destroys up to half the crop. Affected tubers can transmit the disease for several generations without symptoms.
A characteristic feature is a specific yellowish mucus that is released on the cut of wilted leaves; the plants grow dwarf. The disease spreads during harvesting through damage to the tuber skin.
- brown bacterial rot is a quarantine disease.
Potato brown rot destroys up to 70% of the crop in the countries where it is widespread. Since 2011, the pathogen has been detected on ware potatoes coming from warm countries. The disease is still not widespread in Russian planting areas. Infection occurs through the root system.
The first sign is the sudden wilting of leaves, branches and the entire plant. The tuber's vascular ring turns brown and softens. During storage, the pulp turns into dark mucus.
- wet rot turns the tubers into a gray mushy mucus during storage. The disease develops with excessive watering and dense soil.
Wet rot of potatoes spreads quickly when stored in a warm and humid room with insufficient ventilation.
- pitting rot is most often discovered at the end of March. When peeling potatoes, small oily yellow spots are visible. Over time, the affected area expands and the peel bursts in these places;
- Fusarium develops especially actively in hot weather.
Fusarium, or dry rot, on potatoes manifests itself at any time, but especially often during the flowering period, causing the plant to wither. Infection is transmitted through the roots and from one tuber to another during storage.
Dry rot of potatoes affects tubers in the field, but the disease only appears during storage. First, grayish-brown folds appear on them, then the potato pulp becomes loose. And finally, the pulp dries out, cavities with fluffy mycelium appear inside. Fusarium disease of potatoes in storage is transmitted only to tubers with damaged skins.
A fungal disease in the form of rot is late blight, the most harmful and widespread.
Late blight can be identified by the appearance of brown blurry spots on upper leaves, which appear during the closure of the tops. The plant either dries out or rots depending on the weather. Tubers become infected during the growth period; the spots on them are gray-brown, slightly depressed, dense.
Without protective measures, late blight can destroy an entire potato field in 3 weeks. The crop rots during storage.
Important! The infection is not transmitted from one tuber to another.
In addition to the most common types of rot described above, pink, rubber, coal, white, stolon, wound, watery rot and fomoz can also be found.
How to deal with rot
It is impossible to instantly cure any potato disease. The source of infection is located both on the tubers and in the ground. Therefore, to prevent disease and eliminate infection, an integrated approach is always used:
- pre-sowing treatment of tubers with protective agents;
- dressing beds;
- spraying tops;
- processing harvested;
- disinfection of storage areas;
- constant monitoring of potatoes stored for storage.
Important! In the case of bacterial diseases best protection– This is prevention, since there are no complete measures to eradicate the infection.
You should plant only healthy seed material, destroy weeds, treat tubers before planting, observe crop rotation, and apply the optimal amount of fertilizer.
Gardeners knew how to deal with rot even in those days when they were not invented chemical methods protection. To suppress fungal microorganisms, leaves of plants that prevent the process of rotting were placed between the layers of potatoes: rowan, elderberry, wormwood, and sow.
Methods of fighting in our time have expanded through the use chemicals. Before planting tubers or storing them, the following treatment is applied:
- 1% solution Bordeaux mixture or copper sulfate;
- Maxim KS;
- Titus;
- Aktofit;
- Planriz;
- Bitoxibacillin.
When wondering how to get rid of dry rot, we must remember that infection often begins when damaged tubers come into contact with wet soil. Therefore, potatoes should be harvested on dry and warm days, dried before storage, and damaged tubers should be discarded.
The number of manifestations of various infections when processing potatoes before storage with the microbiological preparation Fitosporin is significantly reduced.
Rules for storing potatoes
Before storing potatoes in the cellar to prevent them from rotting, the following preparatory work is carried out:
- remove all remaining vegetables and fruits from last year;
- the walls are whitened with slaked lime;
- shelves and drawers are treated with a 2% solution of copper sulfate;
- A mat treated with a 5% solution of copper sulfate is placed at the entrance.
The air temperature in the cellar gradually decreases with the onset of cold weather. But the optimal one should be kept at +13 °C in the first days. During winter, it should not fall below +2–3 °C with an air humidity of 80–85%. The freezing point of tubers occurs at –1.5° C; at 0° C, the starch in potatoes begins to convert into sugar and the taste of the vegetable becomes sweetish.
Important! You can use beets as a layer of thermal insulation, which better tolerates lower temperatures and protects potatoes from frost.
If an inspection of the stock reveals infected potatoes, you will have to sort through all the tubers and mechanically separate the damaged ones.
Conclusion
Knowing why harvested potatoes rot, you can and should try to prevent the infection from occurring during storage and get rid of it at the first sign of its appearance. Fortunately, the harsh climate of Russia does not allow many diseases to spread throughout the country. However mandatory preventive measures it doesn't cancel it.
“What to do with potatoes so that they don’t rot in the furrow? How to defeat late blight? Is it possible to save berry bushes from birds?
This question was asked to us by Nadezhda Petrovna from Pskov. As it turns out, this problem is relevant now for most gardeners and gardeners. For answers, we turned to our dacha expert Alexey KAZARIN.
Damn late blight
I have never seen such a rainy year in my life. And what to do to protect potatoes from rot? To be honest, I had no real experience. Already these days, in my dacha, late blight is beginning to appear on plants, including tomatoes in the greenhouse.
Warming and dampness everywhere - best conditions for its distribution. Late blight affects not only the potato tops, but also the vegetable itself. Having destroyed aboveground part plants, it then penetrates the tubers during rains. It's her, the damned one, and the reasonannular or bacterialwet rot , with an unpleasant odor
The first signs of late blight usually appear at the beginning of flowering after the tops close. On the leaves, on the upper side, first small, then merging, wet spots appear, which then turn brown. And on the stems, at the border with the soil, a loose whitish coating appears - this beginsconidial sporulation of the fungus.
With the help of wind and rain, the spores are transferred to other bushes, and the infection quickly spreads to the entire area, which becomes brown from dead and drooping leaves. To prevent late blight and rot, strict preventive measures are necessary. Don’t wait until it starts to manifest itself, otherwise it will be much more difficult to fight it.
We don’t wait, we fight!
In such years (and they will now begin to repeat more often), the first spraying copper sulfate(50 grams per bucket) will have to be carried out immediately two weeks after germination, then repeated during the growing season at least 7 - 14 days, and it is especially necessary to do this immediately at the beginning of flowering of the tops. Copper chloride or chloride are suitable for this. More effective for this purpose is the French-made drug RODOMIL GOLD or any other “golds” (“gold” translated as “gold”) intended for farms. They are in a large, about one kilogram, package in the form of a gray powder that dissolves well in water. I bought this box and it has lasted me for several years. Moreover, the drug is universal: the fungicide is suitable not only for protecting potatoes and tomatoes from late blight, but also cucumbers and onions from downy mildew ( powdery mildew), as well as grapes - from mildew. It can only be purchased at plant protection stations. It is necessary to spray first from the bottom of the leaves, and then the entire bush.
Early planting periods contribute to the formation of tubers even before signs of disease appear. But in cold spring Planting too early is also dangerous - the tubers may become infected with rhizoctonosis and then will not sprout at all. In this case, vernalization of tubers and germination of potatoes in sawdust is useful, which significantly shortens the growing season. High hilling before closing the tops also helps. The main thing here is not the height of the ridge, but the change of boundary: the ground is the lower part of the stem. Sporulation does not immediately “take root” here, and covering the border delays the beginning of its development (late blight does not multiply in the ground). Increases resistance to late blight and fertilizing potash fertilizers and microelements - boron, manganese.
IN normal conditions, not in rainy years, mid-early and late varieties. He warned me about this scientist breeder Alexander Udovitsky from Kazakhstan. The tops of such plants are affected, according to my observations, about ten days later, but they still die.
Early planting, early harvesting
I think that now it is necessary to grow only early varieties, the vegetative period of which from germination to ripening is no more than 45-50 days. This is: “Impala” (growing season 45 days). The Bellarosa variety is well established among Pskov farmers (popularly simply White Rose), with light yellow flesh and tall taste qualities, “Alena”, “Ariel”, “Timo”. I'm testing a new one too. early variety“Valery”, the elite tubers of which were given to me for propagation by Udovitsky. During the entire growing period, it is advisable to maintain the soil in a loose state. Why add loose compost, sand and sawdust(better than coniferous species).
And, of course, in this rainy season, it will apparently be necessary to harvest the potatoes a little earlier, without waiting for the tubers to fully ripen. You can do this, if necessary, as early as two weeks after flowering. There is no need to be afraid that such potatoes will not store well, because they still have thin skin. Well-dried potatoes in a dark, dry room gradually become coarser. The main thing is that there are no injuries on it. Before harvesting, be sure to mow the tops so that the tubers hurt less during storage.
Sunflowers will save you from blackbirds
Birds indeed headache for summer residents. There is little benefit from them, without chemicals protection from harmful insects it still can’t be done, and up to 50 percent or more of the berry crop can be destroyed. Blackbirds, forest magpies, and starlings are especially harmful to our gardens. They are omnivorous and gluttonous. They cause great harm not only to currants, gooseberries, strawberries, serviceberry and honeysuckle. In the fall, they spoil apples, pears, and grapes. Magpies and crows often completely “collect” the nuts from the hazel. Therefore, I think it’s not worth attracting birds, for example, by arranging birdhouses for them, as summer residents often do.
The best remedy for birds is to cover the plantings with special nets, available for sale in hardware stores. Covering low bushes and strawberries with light non-fabric materials helps a lot. Last year, my neighbor’s sunflowers helped prevent grapes from pecking in the fall. Birds prefer these oily seeds to berries and are distracted by them, allowing them to ripen without much damage to the owner. Now I plant sunflowers for the children, and partly to protect the vineyard in open ground. In this way you can also distract small birds: tits, wagtails and others.
Scare!
What to do to protect high fruit trees and bushes?
It is, of course, inhumane to shoot birds or poison them. But this would be the most reliable way fight them. It is generally accepted that it is prohibited to catch and poison birds. But according to a long-standing hunting tradition, it is possible. In many countries, hunting for large birds still exists. Among the recipes Italian cuisine, for example, there are quite a few that contain fried, stewed and boiled blackbirds. This doesn’t suit us, and what’s there? However, I think it is also possible to scare away birds in this way. Somehow I bought an air gun for this, but I didn’t have time to shoot, even though I was an excellent shooter in the army. But we should catch these somewhat impudent birds and hang them like a scarecrow. I think it will work well.
It’s strange, but this spring there were whole flocks of blackbirds, magpies and starlings scurrying around everywhere. But in June they suddenly disappeared somewhere. I saw only one dead blackbird once. Now my soul is calmer. I'm really tired of their chirping. Perhaps it's a weed. Or maybe also the result of natural disasters? The future will tell. As for the rest of my advice, read Kuryero carefully and follow them strictly. The main thing is to take care of yourself.
Almost everyone grows potatoes in their garden. It is no coincidence that this vegetable is planted, because it is one of the main components traditional dishes Russian cuisine. Potatoes grow well in almost all regions, including northern ones, and belong to unpretentious plants. But, like any other species, things happen to it. The fruits can rot, causing the entire crop to suffer. Why does this happen, and is there any remedy?
The main reasons for potato rotting in the ground
The vegetable itself is moisture-loving. He demands.
Abundant watering potatoes are needed only during the period of tuber formation, the rest of the time excess moisture will only bring harm.
Still, if moisture standard is exceeded , then this may affect the quality of the crop, and rot may appear on the potatoes. Today, any region is not immune to this, since summer is increasingly rainy. The northern, northwestern and even southern regions. At the beginning of summer, half a month's or even a month's worth of precipitation often falls in one day, which cannot but affect the harvest.
So, they highlight following reasons potato rotting in the ground:
- excessive moisture due to prolonged rains;
- incorrect landing;
- , due to which the entire harvest may deteriorate;
Late blight can spread to the entire area in 2–3 weeks.
- rhizoctoniasis , or black scab (black bumps on a vegetable);
- Alternaria blight (affects the stem, leaves and fruits);
- fusarium, or dry rot (more often caused by improper storage);
- blackleg
(fruits become covered with mucus);
Signs of damage to a bush by black leg in rainy summer.
- wet rot (a fungal disease that penetrates into tubers through cuts);
- ring rot
(appearance of yellow rot on fruits).
Ring rot of potato tuber.
It is worth noting that all potato diseases accompanied by the appearance of rot occur due to improper planting, abundant moisture and rain, as well as improper storage methods.
Potatoes rot in the ground from the rains: how to save the crop in a rainy summer?
After heavy rains, the ground often becomes crusty. Because of it, root vegetables do not receive enough air, as a result of which the potatoes receive little air and can spoil. For a vegetable, it is important that the soil breathes.
Potatoes need to be hilled at least 3 times per season!
If you notice a rotten root crop, it is better to remove it so that it does not infect the nearby roots. A new plant can be planted in its place.
It is very important to control humidity during growth. After the plant has finished flowering, the infected tops can be removed. The fruit will ripen well, in this case summer residents should not worry. This procedure will protect the plant from various fungal infections and rot.
This bush needs to be dug up and seen why it died.
If the tops are not removed in a timely manner, then all the infection will be washed away from her after the next rain into the ground, as a result of which even more root crops may suffer.
Security measures
To protect the potato crop from spoilage and rotting, adhere to the following safety measures:
- Potatoes are not planted in lowlands, but in relatively raised beds
. It is advisable to choose a well-lit place where there will be enough light sun rays. So, the soil will dry out faster from moisture.
A suitable place for potatoes.
- Potato should not be neighbors with tomato, eggplant and pepper. Good neighbors for potatoes: radish, corn. Land on which corn, oats, beets, rye, and flax grew is ideal for potatoes.
- Plants are best planted at temperatures between +15 degrees . Optimal time planting - late April to mid-May.
- If potatoes are planted in a region where there are often rainy summers, then they are planted in high double beds
. Planting depth can reach up to 8 cm. Between the rows there must be at least 30–40 cm. As a result, the potatoes will always be above the level, and the moisture will immediately flow down.
In moist soils, potatoes are planted in high beds.
- So that the potatoes grow better next season, in the fall, it is recommended to plant rye or oats in the area under it. With the onset of spring and after the snow melts, the ground is dug up and seed potatoes are planted. When planting, make the bed high so that the root crop gets enough air.
- Plot with planted potatoes be sure to weed . Remember that weeds often cause moisture stagnation.
- Crops often rot in clay soil. If you are going to plant potatoes in this type of land, then first use fertilizer, and then plant the plants. It's better to choose tall type landings.
- Seed potatoes can be planted whole or in slices. If you choose the second method, then a few days before planting, give the slices time to dry. It is advisable to cut seed potatoes with a disinfected knife. It can be washed in a solution of potassium permanganate. If you still plan to plant the slices immediately after cutting, then use ash, which will prevent rotting. Roll them in ash and place them in the holes.
Processing seed potatoes pink solution of potassium permanganate.
- To prevent rot, it is recommended to treat planting material with Bordeaux mixture, copper casing solution or fungicide.
Diseases and protection against them
In summer, potatoes can rot due to fungal infections caused by heavy rains, moisture, improper planting in clay soil, etc.
There are several types of rot. It can infect stems, leaves, roots, and infect neighboring plants. What to do in this case?
If you notice that the fruits in the ground are rotting, then you can try the drug " Prestige" He provides comprehensive protection fruits
The bushes are fading
If you notice that the bushes have begun to wither and their leaves have turned yellow, then you need to dig up the plant and inspect the tubers. If rotten roots and tops appear, they should be burned immediately.
To avoid potato rotting, be sure to use mineral fertilizing . In this case, in no case should you exaggerate the fertilizer, since excess fertilizing can also cause fungal infection.
Drugs
Sick bushes should be removed, and healthy ones should be treated with a special product.
If you find damage to plants after flowering, notice late blight or other disease , then the tops need to be mowed. Can be treated with a special preparation " Ridomila" Follow the instructions on the packaging.
Other means also help:
- Epin;
- Efal;
- Revus;
- Ditan.
After harvesting, each potato is carefully checked. Rotten fruits should be thrown away or burned immediately.
Damage to the skin of tubers can become a place for infection to enter.
If there is at least one rotten fruit among healthy potatoes, it can eventually infect the entire harvest.
Conclusions
To prevent potatoes from rotting in the ground, they should be planted correctly, choose a well-lit place for planting, and feed the soil correctly.
Potatoes can rot for various reasons, we hope that you have avoided them.
Helps to avoid fungal infections simple measures precautions. If the plant does begin to rot, then special preparations can be used.
The potato harvest is preceded by several months of preparation associated with the hassle of preparing planting material, fertilizing beds, and treating seedlings. Therefore, the disappointment of the farmer, who saw that the long-awaited crop began to rot some time after digging, is difficult to describe in words. To avoid such annoying disappointment, farmers must know about the causes of the problem and effective methods preventing it. They will be covered in this review.
Preventing rot in storage
1. Whitewashing the storage
A cellar, basement or barn used by a farmer as storage for the harvest must be whitened before storing potatoes. Whitewashing the walls will prevent the growth of pathogenic microflora and make the storage microclimate favorable for preserving tubers.
2. Use of smoke bombs
Another effective way getting rid of mold and mildew in storage consists of using smoke bombs. They can be found in specialized garden centers or supermarkets.
3. Treatment of tubers before storage
Widespread antifungal drugs, such as Fitosporin, Maxim, Anti-Rot, etc., are used to treat dug-out, cleaned and dried potatoes before storing them for long-term storage.
4. Proper organization storage
Tubers should be carefully placed in boxes with holes for ventilation. For greater reliability, a layer of tubers is layered with fern or rowan leaves.
5. Timely detection and removal of affected tubers from storage
Periodically, the farmer will need to visit the storage facility in order to sort the potatoes and reject tubers affected by rot.
6. Control over the storage microclimate
Ideal storage of potatoes is possible in a well-ventilated storage facility with a fairly low humidity level. Air temperature also matters - the permissible range is from +2 to +4 degrees.
Video: protecting potatoes from late blight