Bacterial potato diseases – black leg, ring rot and wet rot of potato tubers – are ubiquitous and cause significant damage both in the field and in storage.
The main signs of the black leg are noted soon after the emergence of seedlings of potatoes. Bacteria destroy the base of the plant stem. The stem darkens, often rots in wet weather, the base of the stem becomes thinner, a constriction forms at the border of diseased and healthy tissue, and the plant is easily removed from the soil (without roots).
In the tubers of a new crop, bacteria – pathogens of the blackleg penetrate the stolons, so the lesion begins at the points of attachment of the tuber to the stolon. The penetration of bacteria into tubers can also occur through cracks in the skin and through various mechanical damage. Therefore, when planting, cutting tubers should be avoided.
Often, diseases on potato tubers do not appear in the fall, during harvesting, but at a later time. Signs of black leg tuber disease are easy to distinguish from damage by other pathogens. Rotting of the tuber begins from the site of infection – from the stolon end of the tuber. The tuber tissue in the lesions turns into a soft, slimy dark mass with an unpleasant odor. Later, a rotten cavity or hollow appears here.
The main source of infection is diseased planting tubers. In addition, bacteria can survive in plant debris. Waterlogging of the soil contributes to an increase in the percentage of diseased plants. Therefore, on heavy structureless soils, the disease develops much more strongly than on light soils. Structural soils, on the contrary, contribute to increasing the resistance of plants to the disease. In dry summers, with a lack of moisture and elevated temperatures, the development of the disease sometimes stops, and the tubers do not have external signs of damage, but carry a latent infection that manifests itself during storage or the next year.
The causative agents of ring rot are less active than the causative agents of diseases such as scab and blackleg. The wilting of plants is slower. Bacteria cause a gradual blockage of the vessels of the stem, first the lower leaves wither, then the middle, upper, and only later the stem. Bacteria also penetrate into the tubers of a new crop through stolons, causing destruction of the vascular system. On the cut of the tuber, the rot looks like a ring, so it is called annular. At first, the rot is yellow, then it turns brown, and later the tuber rots completely. When pressed in the area of the vascular ring, a light yellow mucous mass is released.
Sometimes bacteria penetrate into unprotected tubers – through cracks, peeled peel. Immature tubers are especially not resistant to damage, since their skin is fragile and easily peeled off. With such a lesion, at the points of penetration of bacteria into tubers, rot appears in the form of yellow round spots, later pits form at the site of the spots. This manifestation of the disease is called pitted rot.
Thus, the causative agent of the ring (pitted) rot remains in the seed tubers – in a latent state inside the tissues or on the surface of the tubers. Wet rot of potato tubers often occurs during storage. The causative agents of the disease are bacteria commonly found in the soil. The defeat of tubers often occurs with excessive soil moisture. Bacteria penetrate tubers through lentils, mechanical damage, late blight, dry rot, and scab. Frozen and suffocated tubers are severely affected. Further spread of the disease may occur in storage. Wet rot of tubers causes softening of tissues, which subsequently turn into a slimy mass with an unpleasant odor. Even with a weak lesion, the tubers are not suitable for storage.
We increase the resistance of plants
In the fight against potato diseases, all methods aimed at increasing plant resistance and destroying pathogens are important. Of great importance is the selection for planting healthy seed material. In the spring, three weeks before planting, seed tubers are taken out of storage facilities (cellars, cellars, pits) and placed in a warm room with a temperature of about 15 ° C. At the same time, light hardening of the seed material (landscaping) should be carried out, germinating it in diffused light. This technique will increase the field germination of tubers, reduce the development of bacterioses during the growing season and thereby increase the yield.
During the period of spring light hardening – germination, all bacterioses and other diseases appear on the tubers. At the end of spring germination, before planting, the seed tubers are sorted out, all rotten and affected tubers are removed. If planting is delayed or the potatoes grow prematurely (sprouts longer than5 mm), it is again placed in the cellar and stored at a temperature of 2-3 ° C. In this case, the germination of potatoes is preserved. For planting, it is necessary to use dry, slightly germinated tubers with sprouts up to5 mm.
Effectively increases the resistance of potato plants to scab and other diseases, strengthens their immunity and stimulates growth. Treatment of tubers before planting with a growth regulator – the biological preparation AGAT-25K. The main active ingredient of this drug are beneficial soil bacteria – natural antagonists of pathogens. This preparation also contains a physiologically balanced set of starting doses of macro- and microelements, vitamins B1, B2, PP, as well as special biologically active substances from seedlings of various plants that improve potato immunity. It is allowed to process tubers with small sprouts. This drug is very economical in use: its consumption is only7 g on the 100 kgseed tubers. Potato tubers are treated by spraying (1 literworking solution for 100 tubers). It should be noted that AGAT-25K is compatible with fungicides – chemical means of protection against plant diseases. Copper sulphate can be added to the working solution of AGAT-25K at the rate of0.02 g on the 100 kg tubers.
How else to deal with bacterioses of potatoes
As we have already said, cutting seed tubers is not recommended, as this leads to infection of seed tubers with pathogens. If there is not enough planting material, it is better to plant it sparsely. However, if this does not make up for the shortage and you still cut the tubers, be sure to ignite the knife after cutting each tuber on an open fire.
The causative agents of bacterioses remain for a long time (up to two years) in undecayed plant residues. Therefore, when cultivating potatoes, agrotechnical measures are important that accelerate the mineralization (decomposition) of plant residues. These methods include deep autumn digging of the site after harvesting potatoes, the introduction of organic and mineral fertilizers into the soil, as well as the correct choice of predecessor. Crops with increased susceptibility to black leg and wet rot (cabbage, carrots, tomatoes, onions) should not be cultivated as potato precursors in crop rotation, it is better to grow legumes and beets. In the case of a strong manifestation of bacteriosis on potatoes, the site should be disinfected by sowing winter rye or oat mixture.
We advise you to choose potato varieties with increased resistance to bacterial diseases. During the growing season, the fight against bacteriosis of potatoes consists in the timely removal and destruction of plants with signs of black leg and ring rot. Potato plantings should be inspected during the germination, flowering phase and two to three weeks before harvest. These measures are especially important if the seeds are planted with tubers from their own plot.
Proper harvesting and storage is a guarantee of future harvest
Mandatory and basic technique in the fight against bacteriosis is pre-harvest mowing of tops. It prevents infection of tubers during harvesting due to their contact with damaged tops. This event should be carried out 7 days before harvest.
For seeds, it is necessary to select potatoes from outwardly healthy plants, so we advise you to mark such bushes before mowing the tops. Immediately after harvesting, the potatoes are dried in the field for three to four hours, this improves the keeping quality, and protection against wet rot is increased by 3-4 times.
Harvesting potatoes in wet weather is not recommended, since the bacteria that cause black leg, ring and wet rot, under such conditions, easily penetrate into the tubers through mechanical damage and lentils, causing their mass decay. After harvesting, place the potatoes in a barn and hold for 2-3 weeks at a temperature of 15 ° C. During this period, which is called therapeutic, latent infection will appear, ripening will occur and the keeping capacity of tubers will increase. Sort out the tubers before laying them in permanent storage. At the same time, it is useful to plant seed tubers intended for planting next year within 3-7 days. This technique also inhibits the development of bacterioses.
Storages (cellars, basements, pits) no later than a month before laying the crop for the winter, are cleaned of soil and plant residues, structures, walls of bins, storages, ceilings and shields are whitewashed with lime with the addition of copper sulfate (2-3%). The height of the embankment in the bins should not exceed one meter. On the surface of the embankment, in order to avoid sweating of the tubers, beets previously cleared from the ground are laid. For the same purpose, you can use straw, burlap. It is desirable that potatoes in storage do not come into contact with carrots and cabbage, as these crops are affected by the same pathogens of bacterial rot as potatoes.
In winter, the temperature in the storage should not be lower than +2, +4°С. Compliance with all these rules will make it possible to reduce potato yield losses from bacterial diseases and obtain better seed material for further potato production.