Sergey Banadysev, Doctor of Agricultural Sciences, Doka Gene Technologies LLC
In international practice, potato storage diseases include only those that can progress significantly in the post-harvest period, and the development of which largely depends on storage conditions: late blight and pink rot, anthracnose, bacterial rot (ring, dikea, pectobacterium, tuberous scab), oosporosis , wound watery (pithy) rot - typium, silver scab, phomosis, fusarium.
Storage diseases cause great economic damage, as they increase losses and degrade the quality of tubers and planting potatoes.
The growing market for washed packaged potatoes places high demands on defects that are visible on clean tubers (scab,
phytophthora, dry and wet rot, mechanical damage), so the appearance of additional problems with the quality of tubers during storage is highly undesirable.
Each disease has specific biological features, conditions of development and methods of control.
soft rot during storage is usually caused by bacteria of the genus Pectobacterium and Dickeya. Soft rot infection enters tubers in the field through infected stolons of mother plants. In storage, bacterial soft rot is opportunistic and can cause
serious problems in combination with other diseases.
External manifestations of soft rot damage: infected areas become dark (to dark brown), with impregnated
water peel texture.
The internal soft putrefactive tissue has a moist, mushy or creamy texture, contains white or grayish-brown
slime. Affected areas are outlined by a black border separating them from healthy tissue. After the rot dries, the affected areas become white as chalk (photo 2). If the infection has covered a large volume of tubers, a characteristic ammonia smell appears in the storage.
A batch of tubers heavily affected by this disease may have one or more of the following characteristics: chamber volume seems
decreasing; a thick dark liquid flows out of containers or air ducts, an increased temperature and / or an unpleasant odor is noted in the room.
Reasons for the development of the disease:
• extreme wet conditions during growth and harvest;
• ineffective weed control (weeds tend to accumulate this infection);
• infected seeds (they increase the chances of developing the disease in progeny tubers);
• harvesting of immature tubers;
• harvesting at temperatures above 20°C;
• Excessive air leakage in the vault, as well as faulty shutters;
• loose moisture on tubers (condensation, poor airflow/ventilation);
• a large amount of soil in a batch of tubers;
• other diseases such as watery and dry rot.
A large number of "bruises" on the tubers and improper wound healing also contribute to soft rot infection.
Control: current official information confirming the use of bactericides or disinfectants for
little direct control of bacterial soft rot in storage. But it is known, for example, that the synthetic antibiotic streptomycin is widely used in countries characterized by high temperatures and humidity (India, China), as well as in the USA.
Dry rot (fusarium) is a fungal disease caused by Fusarium sambucinum and other Fusarium spp. The fungus enters the tubers through
wounds and bruises caused during harvesting and handling operations. Dry rot symptoms usually first appear around wounds about a month after the tubers are stored. The diseased tissue becomes light brown to black in color. Large, deep, concentric rings that break under light pressure can form on any part of the tuber.
Completely rotted tubers shrivel and mummify. Cavities under the rotten area are usually lined with white, pink, or bluish Fusarium mycelium. Tubers may be soft and moist if soft rot is also present. Inside, the infected areas of the tubers are black and white, with a crumbly mass (photo 3).
There are distinctly fenced off areas between the healthy tissue and the affected one. Their outer surface may be sunken and wrinkled.
Sometimes white or pink fungi can be seen outside. Dry rot development can result in secondary bacterial soft rot.
Conditions conducive to the spread of the disease: dry and warm weather. Keep in mind that the disease can spread quickly if potatoes are not properly treated during the first 2-3 weeks.
In the list of basic recommendations for preventing crop infection
soft rot highlight the following points:
- Thoroughly clean storage and containers before use (and disinfect if diseased potatoes have previously been stored there).
- Store potatoes grown from healthy certified seeds, with controlled watering and nutrition, in conditions of well-built protection against weeds, insects and diseases.
- To ensure the normal formation of the peel and ripening of the crop. Clean with care and avoid bruising, do not clean in the rain. If soft rot infestation is suspected, place batches close to access doors so they can be removed quickly if they start to go bad. If a high percentage of disease is detected during pre-harvest checks or harvest, use low humidity and continuous ventilation during curing/early storage.
- Organize the correct exposure of healthy potatoes for 2-3 weeks at a temperature of 10-13 ° C and a humidity of 95%. Keep main storage temperature below 5°C. Do not use moisturizer. If the disease is noticed after treatment, then the decrease in temperature to holding conditions should be rapid, with plenty of ventilation air. Prevent the formation of condensation on tubers. Ventilation systems that can provide a continuous but low velocity air supply prevent free moisture build-up. Use continuous ventilation without humidification for severely affected areas. Isolate such parties, if possible.
A favorable environment for the growth of the disease is created in storage facilities if too much soil is supplied there along with potatoes. Potato bruises during harvesting and processing contribute to rapid infection.
Control: Minimize bruising during harvest and handling. Avoid harvesting when the flesh temperature is low because cold potatoes are very susceptible to bruising. Before harvesting, make sure that the potatoes are properly skinned and ripe. Remove excess dirt and clods of earth during cleaning and before the treatment period. It is recommended to carry out treatment at 13°C and 95% relative humidity, which promotes wound healing. Wound healing should be completed in 2-3 weeks. After completion of treatment
period, gradually reduce the temperature at a rate of 0,5 ° C per day to the level of long-term storage.
Pink rot is a relatively new dangerous fungal disease caused by the oomycete Phytophthora erythroseptica. External signs of damage: wilting of the aerial parts of plants, symptoms of chlorosis on the leaves.
Potato tubers become infected through sprouts, lentils and wounds, usually in the field. Affected outer tissue on the tuber may have
brown discoloration, especially around natural openings (lentils) and in sprouts. Internally, the infected area spreads in an almost straight line through the tissue of the potato. When affected tubers are cut, the inner tissue becomes spongy and turns pink after 30 minutes (photo 4). In later stages, the affected tissue may exude a clear, odorless, watery liquid when compressed.
Conditions conducive to the spread of the disease: excessive moisture in the fields at the end of the growing season and hot weather (air temperature above 35°C).
Control: Avoid over-watering at the end of the growing season, especially when temperatures are high. Examine low-lying stagnant areas of the field; if symptoms of pink rot are found, do not remove such areas. If the disease is detected after the potatoes have been stored, ensure sufficient airflow and a temperature of 7-10°C for the drying time. If
only a small part of the batch is affected, treat healthy potatoes at 10°C. Subsequently, apply rapid cooling at
continuous ventilation.
Watery wound rot is a fungal disease caused by the oomycete Pythium ultimum (a soil fungus that infects through lesions and natural holes in the potato skin). Internal affected areas are usually clearly separated from healthy tissue by a dark border. The rotten tissue has a spongy texture, while the affected areas can only be inside, leaving the peel intact (photo 5). The cut fabric becomes white, gray and dark brown. The disease may appear within 2-3 weeks of storage. The first sign of a problem is the appearance of wet spots on the bottom rails of containers due to wetting with watery liquid from affected tubers.
Conditions favoring the spread of the disease: Extremely high humidity followed by a short period of dryness during tuber maturation. The disease is especially disturbing if the temperature of the tubers exceeds 20°C. Pythium increases the risk of infection with bacterial soft rot, but wound rot itself does not spread in storage.
Control measures for watery rot are aimed at preventing situations that favor infection and disease. They include in
choose fields with good drainage and no history of disease, at least a three-year crop rotation. Avoid excessive
irrigation, especially at the end of the season, to allow enough time for haulm desiccation and good skin formation. Tubers should be harvested in cool, dry conditions when the skin has matured and the flesh temperature has dropped below 20°C.
If the symptoms of the disease began to appear in the storage, then the temperature in the room should be reduced to 12-15 ° C and the circulation of dry air should be increased. Fungicide treatments during the growing season and storage in the fight against Pythium ultimum are quite effective - just like
and in the fight against rose rot, silver scab, anthracnose and fusarium. This will be discussed in detail below.
Phomosis (gangrene) - an increasingly widespread fungal disease of stored potatoes. First
symptoms of gangrene are small round dark indentations that may appear dark gray or brown. The indentations resemble thumbprints and may coalesce and overlap (photo 6). The spots usually have a tendency to stretch across and thus differ from the concentric rings characteristic of Fusarium. Gangrene rots are often very dark and have a clear border with healthy tissue.
Conditions conducive to the spread of the disease: Phomosis infection most often occurs when the harvest is delayed due to cold and wet weather. The infection enters the tubers through damage to the skin. A favorable environment for the development of gangrene can also form in storage if potatoes are stored in colder conditions (compared to the standard) and / or high-quality healing of skin damage is not carried out.
Control: the best prevention of the disease is to reduce damage during processing. The second necessary condition for preventing the spread of infection is the annual cleaning and disinfection of the storage. Early harvest and dry curing will also help avoid problems. At the beginning of storage, the fungicides thiabendazole and imazalil are effective in controlling the disease.
Anthracnose or black spot of tubers - a widespread disease, the causative agent is the fungus Coccodes Colletotrichum. Tuber manifestations of the disease are brownish-gray discoloration of the skin, rounded or irregularly shaped areas (photo 7). Lesions can take on a silvery sheen, making it easy to confuse anthracnose with silver scab. The main difference is spots of irregular
shapes with fuzzy margins and regularly spaced black dots.
Control: use of certified seed, treatment of tubers that does not necessarily limit anthracnose,
but improves plant health and energy, reduces stress and thus increases resistance to anthracnose. Use of balanced fertilizer and sprinkler irrigation to reduce plant stress, timely destruction of weeds (reservers of latent anthracnose infection). Exclusion of soils with unregulated water and air regime, which tend to form a thick crust. Crop rotation with crops that are not susceptible to the pathogen - such as cereals, soybeans, corn. Sufficiently deep plowing
which contributes to the decomposition of plant residues. Harvest immediately after potato ripening. Accurate control of temperature and humidity in storage: high temperatures and condensation of water vapor contribute to the development of the disease.
Silver scab. The causative agent is the fungus Helminthosporium solani. The disease is ubiquitous. The main sources of infection are affected planting tubers. Symptoms of the disease can be detected already during harvesting or shortly after laying in storage:
these are inconspicuous light brown, without shine, spots of various sizes and shapes (photo 8). By the end of storage, the disease reaches mass development, and the affected tissue acquires a well-defined metallic or silver sheen. Mushroom on the surface of spots
develops conidial sporulation and small punctate black sclerotia.
With a strong defeat, the potato peel begins to wrinkle, its throughput increases, as a result of which moisture loss occurs. Silver scab is a classic storage disease. Often, when stored in storage, the crop looks free of it, and
by the time of landing, 100% infestation is detected. During transportation, diseased tubers come into contact with healthy ones, and under conditions of a sharp change in temperature, humidity, shaking and ventilation, a massive manifestation of symptoms and overinfection of healthy tubers occurs.
Control: Practice good crop rotations, at least a three-year rotation. The use of seeds without the presence of a silvery coating. Checking purchased seeds for the presence of silver scab. Separation of seed lots of different generations during storage (should not be placed in the same storage). Use of registered seed tuber products at planting.
Harvesting potatoes immediately after the peel is strong. Adequate setting of the combine. Thorough cleaning and disinfection of storage and all equipment before the new season. Checking potatoes for silver scab infestation before storage. Separation of lots with silver scab from those with almost no infection. Application of post-harvest treatment for disease control during storage. Treatment of tubers in conditions of high temperature (10-15°C), humidity (90%) and good ventilation (highest air flow). Immediate cooling of potatoes after treatment to the desired level of main storage. Organization of storage in conditions
special temperature regime: at the lowest optimum range for a given direction of potato use. Prohibit partial shipment if long term storage is planned.
mixed infection. Tubers are rarely affected by only one pathogen. As a rule, analysis of a diseased tuber confirms
the presence of several types of pathogens (photo 9).
Mixed fungal and bacterial infections cause much greater losses than individual infections. Apparently, different pathogens stimulate each other's growth.
Since storage diseases can lead to large crop losses, the fight against them must be systemic, including directly.
at the storage stage. On the example of a number of diseases, it has been proven that the risk of diseases can be reduced by minimizing mechanical damage (which stimulate the development and spread of all warehouse diseases) and the use of varieties with genetic resistance to pathogens.
Disease control is a fundamental component of a seed storage management system. Few of them occur
in storage, the main sources of infection are usually seeds or soil.
Therefore, the main protective effect is provided by the selection of healthy predecessors, work on uninfected fields, the use
high-quality seed material, good soil drainage, optimal watering, timely and high-quality harvesting.
The following actions contribute to reducing the likelihood of developing diseases:
• timely removal/drying of tops to ensure a reliable, durable peel;
• Efficient harvesting to quickly fill storage;
• optimized airflow for efficient drying and cooling;
• prevention of formation of condensate;
• good hygiene of storage and equipment.
Harvesting in conditions when the potatoes have already formed a strong skin, gentle organization of transport and storage
- all this is important for ensuring the safety of products, since diseases penetrate into tubers mainly through external damage. During harvest, cracks and cuts in tubers are inevitable and pathogens spread throughout the batch of potatoes. But whether the disease develops in storage depends on three key factors:
• the amount of disease inoculum, usually fungal spores or bacteria, present on the tubers;
• microclimate conditions;
• natural tuber resistance to disease.
Containment of diseases at the storage stage is possible by minimizing damage, quick drying, high-quality healing of damage, temperature and humidity control, and hygiene. Schematically and in the context of diseases, this is shown in Table 1.
Universal storage disease control techniques:
• Harvesting dry, healthy potatoes with a pulp temperature between 7 and 15°C. Maximum removal of damaged tubers on a combine, providing conditions for the high-quality performance of this work.
• Careful preparation of storage and air supply system. It is important to make sure in advance that sufficient airflow rates are provided in all areas of the storage. Add portable active ventilation systems to rooms with general ventilation. Good air movement is absolutely essential for storing problem potatoes.
• Correction of drying, curing and cooling regulations. Problem potatoes are usually wet and infested with rot-causing organisms, the farmer's task is to cool and dry the crop as soon as possible. Cool quickly to final storage temperature (3-5°C). Do not moisten diseased potatoes.
• Run the fans (install more if necessary) in continuous operation until the crop is dry. The circulation of air through the potatoes must be carried out constantly during the entire problem period, even if there are no conditions for the use of outside air.
• Ensuring the movement of air through the product layer. Rotting potatoes and dirt create obstacles. Fans with high air flow pressure are required.
• Daily monitoring of storage. Infrared "guns", thermometers in various zones provide a good indication of the average temperature.
• Exclusion of exposure to warm outside air on cold potatoes (otherwise a layer of free water will condense on the tubers). Water on the tubers tends to choke the potatoes and creates a favorable environment for soft rot bacteria. The air temperature should be about 1 degree C above the desired tuber temperature.
Fungitsidы can be applied during loading, during storage and when shipped from storage.
Active ingredients used to treat potatoes against diseases before storage:
• RF - fludioxonil, benzoic acid, colloidal silver, Bacillus subtilis;
• Germany – imazalil, pencicuron, prothioconazole;
• England, Belgium - imazalil, thiabendazole;
• France – flutalanil, mancozeb, pencecuron, prothioconazole, fludioxonil;
• Canada - thiabendazole, fludioxonil, azoxystrobin, difeconazole, phosphorous acid, potassium phosphite, Pseudomonas suringae;
• USA - azoxystrobin, fludioxonil, difeconazole, sedaxan, mancozeb, flutalanil, penflufen, prothioconazole, thiophtanate-methyl,
phosphorous acid, potassium phosphite, chlorine dioxide, peroxyacetic acid.
Seed treatment should provide protection against diseases and pests, stimulate plant development and be sufficient
technological.
The effectiveness of the operation directly depends on the quality of its implementation and the correct selection of preparations; it should be based on an understanding of the intended purpose of specific fungicides and taking into account the phytopathological problems of a particular batch of planting material and a particular field. In the official state catalog of pesticides of the Russian Federation, tuber dressing fungicides are registered as a means of controlling rhizoctoniosis, common scab and silver scab. However, there is no data on the effectiveness of drugs against
anthracnose, wound watery rot, soil late blight infection, which have become widespread in recent years. So, the long-known TMTD is positioned as a remedy against late blight, rhizoctoniosis, scab, wet bacterial rot and fusarium. This raises reasonable doubts, since only the most modern three-component fungicide Idicum has a comparable spectrum of action (against oosporosis, phomosis, anthracnose, fusarium, rhizoctoniosis).
The most complete set of means for protecting potato planting material is presented in the USA. For liquid pickling, in addition to substances known in the Russian Federation, sedaxan, hydrogen peroxide, Chenopodium quinoa saponins bacteria are allowed to use. Sedaxan is included in the world's first four-component disinfectant from Syngenta, which in the USA is called Cruiser Maxx Vibrance Potato Ultra with a combination of dv-in fludioxonil + difenoconazole + sedaxan + thiamethoxam. The Russian Federation announced the start of the procedure for including a similar drug in the registry for potatoes.
It is officially allowed to use 16 active ingredients of fungicides, 10 a.i. for seed treatment. insecticides and 15 microbial preparations with fungicidal activity. Fludioxonil, cyproconazole, benzoic acid are effective against potato diseases,
benomyl, pencycuron, thiabendazole, penflufen, prothioconazole, difenoconazole, thiram, imazalil, metalaxyl, iprodione. There are several products with two A.I. fungicides: penflufen + prothioconazole; in combination with an insecticide - acetamiprid + fludioxonil + cyproconazole,
thiamethoxam + difenoconazole + fludioxonil, iprodione + imidacloprid + difenoconazole. The richest composition of the three-component fungicide: fludioxonil + imazalil + metalaxyl.
Advance dressing has a number of advantages: a quieter mode, a more accurate dosage of the working solution, and an increase in the productivity of planting potatoes. But high-quality treatment at the hospital is ultra-low-volume spraying with a flow rate of
working liquid no more than 3 l/t. This is possible when using disc atomizers on any rotating surface - hopper rollers, inspection tables or Mafex special equipment. The flow rate of the working fluid of 10-20 l / t at the hospital, which is allowed by the standards of the Russian Federation, should be recognized as erroneous and unacceptable. In the modern phytopathological situation, the obvious wetting of tubers is a deliberate provocation of the development of bacterial diseases. After processing at the hospital, even on the eve of planting, the potatoes must be dried,
otherwise, problems with germination and rotting of tubers are inevitable.