Why potato rot during storage? And how to avoid it

Why potato rot during storage And how to avoid it
Why potato rot during storage And how to avoid it

Although potatoes are available at markets all year round, we want our own incredibly tasty, digestible, and environmentally friendly potatoes. But often home-grown potatoes are impossible to preserve until spring.

After the New Year holidays, the tubers begin to “go bad”, developing unpleasant odors and even (as written in the newspapers) explosive conditions, with gases building up in the enclosed space. So, what causes potato rot in tubers and how can you avoid it?

Let’s deal with the causes and make a plan for preserving the harvest of our favorite potatoes.


Potatoes can be affected by fungal and bacterial diseases during the growing season and during storage. Among the fungal infections, the most damaging are Phytophthora infestans, Fusarium wilt, and Alternaria leaf spot.

Phytophthora infestans

Phytophthora infestans refer to the most dangerous fungal disease. This fungus affects the culture during the growing season (it can destroy up to 70% of the crop in a short time) and is transferred to storage with the tubers.

On the surface of the tubers, hard gray spots appear, which are easily found on the flesh when you cut open the potato. As the fungus grows, the process of tuber decay begins.

Control measures
If the plant is infected during the vegetative stage, the potatoes must be sprayed with a 2% chemical disinfectant to water solution. If the infestation is suspected to be complex (i.e. several fungal diseases), use a bio fungicide, etc.

Optimal storage conditions are well ventilated, without light, with 80-90% humidity and air temperature not higher than 35-37°F (2-3°C). High temperatures of 68-75°F (20-24°C) are required for the development of phytophthora. Therefore, it is not recommended to store potatoes in the high temperatures of the living room.

Fusarium wilt

As with Phytophthora infestans, it affects the tops and tubers during the growing season. Excessive soil moisture (prolonged rainfall) and high temperatures contribute to the rapid spread of the disease.

During the vegetative stage, the external symptoms of the disease appear as gray spots on the leaf surface and general wilting and drying of the plants. Affected plants wilt within a day. a distinctive feature of culture failure caused by Fusarium wilt is a blue-black ring on the stem cuttings (blood vessels clogged with fungal mycelium).

Tubers placed in storage are covered with white patches, or the epidermis wrinkles and becomes dry where gray-brown spots are present (without any obvious reason for violating storage rules). The cut shows dark cavities filled with fungi.

Control measures
Its harmfulness is very high. Mycotoxins of this disease are preserved not only on crops but also on processed products. They affect the nervous system in humans and cause the death of birds and animals. Tubers affected by Fusarium wilt disease (as well as other products – flour, juice, jam, animal feed) cannot be used as food.

During vegetation, spray plants with 1-2% solution of biocide.

Optimal storage conditions are the same as those for preventing phytophthora. It is recommended to treat tubers with organic fungicide phytosporin (bio fungicide, which does not affect human and animal health) when they are put into storage. Harvest potatoes systematically (be careful not to break the outer skin, as infection can spread quickly to neighboring tubers).

Alternaria leaf spot (potato dry spot)

This disease is similar to phylloxera in its damage to potato yields. It affects all parts of the plant (stems, leaves, and tubers). It is most common in mid-and late-season potato varieties recommended for winter storage.

During the growing season, lesions appear as large concentric spots on leaves and stems. The spots gradually turn brown or dark brown with a brownish tinge. On the surface of the tuber, sunken spots appear and gradually shrivel. On the cut surface of the tuber, the affected area is necrotic and differs from healthy tissue by having hard dense, dark brown flesh.

Control measures
Treat tubers with biological and other preparations from the recommended list at the time of preparation for planting. During the growing season, carry out the same treatments as for the previously mentioned diseases.

Optimal conditions for potato storage are the same as those used to prevent the aforementioned diseases.

The aforementioned diseases (Phytophthora infestans, Fusarium wilt, Alternaria leaf spot), as well as Rhizoctonia, scab, rot, and anthracnose, are mainly spread by seed. Therefore, growing and breeding disease-resistant potato varieties that can adapt to external conditions is a key basis for preserving tubers during winter storage until the next harvest.

What causes potato rot in tubers
What causes potato rot in tubers


In addition to fungal diseases, potatoes are also susceptible to bacterial diseases. The source of infection is the rot fungus, which can turn tubers into a gray rotting mass with a pungent, unpleasant odor within 2-3 months.

The bacterial infection occurs under poor storage conditions (poor ventilation, high temperatures, and high humidity). The pathogenic bacteria penetrate the tubers through external injuries (cracks, cuts made during excavation, etc.).

The bacterial infection is spread mainly by seeds, but during the vegetative phase, it attacks not only tubers but also plant organs (stems, leaves, roots, and stolons).

During the epiphytic year, the bacterium kills up to 50% of the crop in the field and up to 100% of the crop during storage. Healthy tubers are mostly infected by phytopathogenic bacteria during preparation for planting, careless harvesting (with various mechanical damages), and sorting before storage.

Among bacterial diseases, potatoes are most often affected by wet bacterial rot, button rot, ring rot, and black tibia.


Yield losses can range from 1-2% to 50-70%. Bacterial diseases affect the nutritious parts of the plant and the tubers. It is difficult to get rid of the bacterial infestation, this is because there are still no varieties resistant to this disease.

When planting infested material, many potato seedlings drop or the seedlings are very weak and do not develop well. As the potato plant ages, the lower part of the stem turns black (hence the name “black stem”) and the leaves turn yellow, brittle, and hard.

The leaves twist into a boat shape, and the leaves themselves grow at an acute angle to the stem. When excavated, the mother tuber is decayed and spongy.


A bacterial infection that affects all parts of the potato plant. Its symptoms during the growing season are similar to those of Blackleg in that the above-ground parts wilt and the mother tuber rots.

A distinctive feature of the disease is a mosaic of light yellow tones on the leaves, as well as swollen leaf nodules. From the mother, tuber grows 1-2 weak stems. At harvest, pitted rot can be seen on the diseased tubers; when cut, the diseased tuber tissue has circular lesions of vascular tissue or yellow subcutaneous blotches.


Ralstonia is one of the most devastating bacterial diseases. It is characterized by a rapid disease course. It affects about 200 plant species, including potatoes.

It is prevalent mainly in areas with warm climates. The sources of infection are diseased tubers and soil, weeds, and irrigation water. The pathogen penetrates the tubers of new crops through mechanical damage, stomata and fills the vessels of stems, stolons, and roots with mucus masses, causing plant wilting and death.

Symptoms of the disease manifest externally at the flowering stage as wilting of the leaves at the end of the shoots. The green leaves turn brown, curl in half and hang down. The roots of the stems become soft. Bacterial slime accumulated in the interior (vascular ring) is released through cracks in semi-decayed stolons, stems, and decayed tubers.


All bacterial rot diseases (as shown above) are characterized by widespread wilting of stunted potato bushes during the growing season and rapid decomposition of tubers into a slimy mass during storage. A large proportion of the rot is a soil pathogen that can remain in the soil for a long time, affecting the healthy material grown.

Therefore, the main measures to protect the crop from bacterial infection are the use of local potato varieties resistant to bacteria, mandatory fall and spring disinfection of the soil before planting, treatment of planting material to inhibit soil infection during tuber germination, preparation of storage facilities and sorting of tubers before putting them into storage.


Based on all of the above, it is clear that poor preservation of tubers in cold periods begins with violations of cultivation and harvesting techniques for this culture. This is followed by storage facilities (cellars, basements, vegetable plots, balconies, huts, etc.) that are not prepared for storing the product, improper selection of potato varieties, and violation of storage techniques.

All these causes lead to different fungal, mold, and bacterial diseases attacking tubers; they also promote the rapid spread of tubers, causing yield losses not only during the growing season but also during storage.

In order to protect potatoes from rot during storage, it is necessary to properly prepare plots for this crop. Fertilizers, fertilizers, pest, and disease control methods can be applied only in accordance with the technology and recommendations.

In planting (for the purpose of long-term storage of tubers in cold periods) it is necessary to use only experienced, medium, and late varieties (by maturity date), resistant to fungi and other diseases. Before sowing, it is necessary to carry out the necessary treatment of seeds.

During the vegetative phase, you need to treat the plants at the beginning of the disease, rather than waiting for a large-scale infestation. It is more practical to follow a pre-determined program of preventive treatment.

Only absolutely healthy and undamaged tubers should be stored in prepared storage.

Meeting the basic requirements for tuber preparation, planting, care and harvesting will minimize crop pests during winter storage.


  1. When several potato varieties are grown on a plot, each variety should be harvested separately.
    Only medium-, late-maturing and late-maturing potato varieties should be stored. early maturing potato varieties after December are no longer suitable for consumption and remain as planting material, or are used as animal feed.
  2. To ensure the full maturity of the tubers, trim the potato leaves 10-15 days before harvest.
  3. Potatoes are usually harvested in dry, sunny weather. If the weather is rainy, the potatoes should be gently dried and the picking dirt cleaned off by hand (to prevent mechanical damage, as fungal or bacterial infections can penetrate the tubers in this way).
  4. Mechanically damaged and diseased tubers should be stacked in separate piles.
  5. Healthy, undamaged potatoes should be moved under a canopy (shaded from the sun) or to a well-ventilated dark room for 5-7 days to allow the upper skin to mature (thicken). To prevent potatoes from turning green, they must be protected from light. When exposed to light, lycopene is formed and the tubers should not be eaten.
  6. Before storage, they should be purified and dried.
  7. To prevent decay during storage, they can be treated with biological agents “phytosporin” and “antiseptic” to reduce the background of infection. They are harmless to humans and animals.
  8. If potatoes are stored in bulk, it is better to spread 1-2 rows of beets on top. It will absorb excess water and thus protect the tubers from rotting. The beetroot will not be affected.
  9. It is recommended to store potatoes in separate boxes (separate for each variety).
  10. At least once a month, re-clean diseased tubers and remove them.
  11. Good ventilation will protect the stored product from infection and decay.
  12. The temperature of the storage room should be between 35-39°F (2-4°C) and the humidity should be between 80-91%. If the humidity in the room is high, in addition to ventilation, place a container with quicklime and replace the filler if necessary. With the arrival of spring, the temperature in the storage room may rise. Freezing water in plastic bottles with a capacity of 3-5 liters will help to reduce it. Ice containers can be placed in different places. Ice cubes in closed containers will gradually melt and cool the room.

Dear readers

If you still have questions after reading the article, feel free to discuss them in the forum or in the comments of this material. Many experienced gardeners have their own secrets for the effective protection of potatoes against fungal and bacterial infections. We would be grateful to receive your tips.

We will be happy to hear your thoughts

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