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Diseases of vegetable crops, in general, are an unpleasant thing, and when special pesticides do not yet exist to fight diseases, this does not add optimism to most gardeners. Nevertheless, bacterial diseases of potatoes can and should be learned to cope with, since they are widespread and can destroy up to half or more of the annual crop.
Potato ring rot is one of the bacterial diseases and is found everywhere in all areas where potatoes are grown. The disease is insidious, since its symptoms develop rather slowly and are not immediately noticeable from the outside, although crop losses can be up to 40-45%. In this article you can find a photo of the signs of the disease, as well as its description and methods of treatment. It is only necessary to immediately understand that in the case of ring rot, treatment as such is usually not carried out. Infected plants are subject to immediate destruction – it is impossible to save them. But the prevention of the disease plays a very important role.
Signs of ring rot disease
Ring rot is caused by Clavibacter michiganensis subsp. sepedonicum or otherwise they are called Corynebacterium sepedonicum. They belong to a variety of aerobic bacteria.
Signs of the disease appear on the roots, tubers, stolons, and the stems and leaves of potatoes are also affected. Infection, as a rule, begins with tubers, but the first symptoms of the disease can only be seen when they are cut, so if the tubers are already in the ground, then the disease can be tracked only by the aerial part of the potato bush.
There is a wilting of one or two stems in the bush, and they quickly fall to the ground. This fall is already a characteristic sign of ring rot, since in other diseases (verticillium, fusarium), wilted stems remain standing. Then brown spots appear on the tips of the leaves of withered stems. Sometimes the leaves of affected stems may turn white due to loss of chlorophyll.
The fact is that bacteria, moving from an infected tuber through stolons to the stems of a potato bush, accumulate there and cause clogging of blood vessels. As a result, nutrient fluids cannot reach the upper part of the plants, and the leaves first lose their turgor and then wither. In addition, the causative agent of the disease releases substances toxic to potatoes.
As a result of a significant defeat by ring rot, the following symptoms are observed:
- The upper leaves of the entire bush begin to turn yellow and curl.
- The surface between the veins of the leaf acquires a fawn color, so the leaves become, as it were, speckled.
- The lower leaves of the bushes become lethargic and thin, their edges can twist upwards.
- Internodes are shortened, potato bushes become dwarfed.
All these symptoms are well illustrated in the photographs below.
If you cut off a diseased stem and place it in water, then light yellow mucus will clearly flow from it. At the same time, the affected stems are not easily pulled out of the ground, since the sinewy structure of the shoots and root crops is destroyed.
Potato tubers, still slightly affected by the infection, practically do not differ from healthy tubers in appearance. But if you make a transverse incision, then yellowing and softening of potato tissues can be observed along the vascular ring. In the photo below, you can see what ring rot of potatoes looks like on a tuber in the initial phase of infection.
As the disease develops, the vascular system of the potato begins to completely collapse and turns into a slimy mass, which is squeezed out when the tuber is pressed.
Two forms of the disease
There are two forms of damage to potato tubers by this disease: pit rot and ring rot. Pit rot is usually the primary form of this bacterial disease. Plants are usually infected in autumn during harvesting. At first, no signs of disease on the tubers can be seen. The disease can begin to appear only 5-6 months after storage, at the very beginning of spring. Under the skin, where infection has occurred, light spots are formed, no larger than 2-3 mm in size. In the future, they begin to increase and reach 1,5 cm. The pulp in these places begins to decompose and a hole forms.
If, in preparation for planting, such tubers are not tracked and planted in the ground, then the disease will begin to develop and the infection will pass to the tubers.
Infection with ring rot usually occurs from old tubers, through stolons and symptoms in the form of necrosis of the vascular ring appear already on young tubers.
Conditions for the development of the disease
Since there are no chemical measures to combat potato ring rot, it is necessary to understand the sources of infection and the conditions for the development of the disease as best as possible in order to understand what preventive measures should be taken in order to protect yourself from this disease as much as possible.
Ideal conditions for the development of the disease are moderate temperatures (from + 20 ° C) and high humidity. It should be borne in mind that at high temperatures and dry conditions, the development of the disease stops, and although the aerial part of the plants quickly fades, this practically does not affect the tubers. They look quite healthy.
The main source of infection persistence and its transmission to new generation tubers are already affected tubers. Unlike some other pathogens, ring rot bacteria do not persist in the soil and do not overwinter. But they may well be preserved in unheated rooms on any plant debris or garden tools and, of course, on stored tubers. At the same time, healthy tubers can become infected by contact with affected specimens, especially if the former have damage to the skin, scratches, bare areas or cuts. That is why it is better to store all cut potatoes separately from the main crop and use them as soon as possible for their intended purpose.
The infection is also easily transmitted through tools when harvesting potatoes and especially when cutting tubers.
It is still difficult to fight the disease, because its causative agent is quite capable of moving from tuber to tuber over several generations without any visible symptoms, if suitable conditions for its development do not occur. Therefore, sometimes it turns out that by planting outwardly healthy tubers, you can get diseased plants.
Ways to fight the disease
The main measures to combat ring rot include the following agricultural practices:
- Use of potato varieties resistant to this disease. When choosing the right variety, keep in mind that early potato varieties are most prone to ring rot.
- During the entire growing season, timely detection and removal of diseased plants.
- If you are seriously struggling with ring rot, then it is imperative to observe crop rotation and do not return the potatoes to the same place earlier than after 3 years.
- Before laying the tubers for storage, the tubers should be well dried and heated for 2 weeks at temperatures not less than +16°+18°C to identify infected specimens.
- Mowing and destroying potato tops a week or two before harvest reduces the risk of infection.
- Treatment of storage with formalin before laying tubers.
- Sprouting seed potatoes in the light also reveals infected tubers.
Many gardeners successfully fight bacterial and fungal diseases of potatoes, including ring rot, by sowing green manure. Oats, rye, wheat, barley, corn, legumes, tobacco, and cabbage are the best crops to deal with pathogens. It is necessary to select fast-growing crops that are able to form a sufficient amount of green mass from harvesting potatoes to frost. In early spring, the field intended for planting potatoes must be planted with mustard or oats. Before planting potatoes, green manure is mowed, the earth is loosened and mixed with plant residues. Saprophytes that develop in the soil can significantly inhibit the development of bacteria.
Finally, you can try to use some ready-made preparations to combat this disease. Both before planting and before storage, seed potatoes can be treated with fungicides Maxim, Quadris or Gamair biological product.
Before planting, it also makes sense to pickle the tubers with TMTD.
As you can see, if you use all of the above means and methods in complex protection, then even potato ring rot will not be scary for you.
