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Diseases of vegetable crops, in general, are an unpleasant thing, and when there are still no special pesticides to fight diseases, this does not add optimism to most gardeners. However, with bacterial potato diseases you can and should learn to cope, since they are widespread and can ruin up to half or more of the annual harvest.
Ring rot of potatoes is just one of the bacterial diseases and is found everywhere in all territories 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 photos 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 - they cannot be saved. But the prevention of the disease plays a very important role.
Signs of ring rot disease
Ring rot is caused by bacteria of the species Clavibacter michiganensis subsp. sepedonicum or in another way they are called Corynebacterium sepedonicum. Refers 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 be noticed only when they are cut, therefore, if the tubers are already sitting in the ground, then the disease can only be tracked along the aerial part of the potato bush.
One or two stems wilt in the bush, and they quickly fall to the ground. This fall is already a characteristic sign of ring rot, since in other diseases (verticillosis, fusarium), wilted stems remain standing. Then brown spots appear on the tips of the leaves of the wilted stems. Occasionally, the leaves of the affected stems may turn white due to the loss of chlorophyll.
The fact is that bacteria, moving from an infected tuber along the stolons to the stems of a potato bush, accumulate there and cause clogging of blood vessels. As a result, nutrient fluids cannot enter 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 that are toxic to potatoes.
As a result of a significant lesion with ring rot, the following symptoms are observed:
- The top leaves of the whole bush begin turn yellow and curl up.
- 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 curl upward.
- The internodes are shortened, the potato bushes take on a dwarf appearance.
All of these symptoms are well illustrated by the photographs below.
If you cut off a diseased stem and place it in water, then light yellow mucus will clearly flow from it. In this case, the affected stems are not easy to pull out of the ground, since the sinewy structure of shoots and roots is destroyed.
Potato tubers, still slightly infected with infection, practically do not differ from healthy tubers in appearance. But if you make a cross-section, then along the vascular ring you can observe yellowing and softening of the tissues of the potatoes. In the photo below, you can see how the ring rot of potatoes looks on the 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 mucous mass, which is squeezed out when the tuber is pressed.
Two forms of the disease
There are two forms of damage to potato tubers with this disease: pitted rot and ring rot. Pit rot is usually the primary form of this bacterial disease. Plants are usually infested during the autumn harvest. At first, it is impossible to notice any signs of the disease on the tubers. The disease can begin to manifest itself only 5-6 months after storage, at the very beginning of spring. Under the peel, where the infection has occurred, light spots are formed, no more 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 fossa is formed.
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 spread to the tubers.
Ring rot infection usually occurs from old tubers, through stolons and symptoms in the form of vascular ring necrosis appear already on young tubers.
Conditions for the development of the disease
Since there are no chemical measures to combat ring rot of potatoes, 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 maximally protect oneself from this disease.
The 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 arid conditions, the development of the disease stops, and although the aboveground part of the plants quickly withers, this practically does not affect the tubers. They look quite healthy.
The main source of infection preservation and its transmission to new generation tubers is already infected tubers. Unlike some other pathogens, ring rot bacteria do not survive in the soil and do not overwinter. But they may well be stored in unheated rooms on any plant residues or garden tools and, of course, on stored tubers. In this case, healthy tubers can become infected by contact with affected specimens, especially if the former have skin damage, scratches, bare areas or cuts. That is why, it is better to store all cut potatoes separately from the main harvest and use them as soon as possible.
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 pathogen is quite capable of passing from tuber to tuber over several generations without any special visible symptoms, if suitable conditions for its development do not come. Therefore, sometimes it turns out that by planting seemingly healthy tubers, you can get sick plants.
Ways to fight the disease
The main measures to combat ring rot include the following agrotechnical practices:
- Use of potato varieties that are resistant to this disease. When choosing a suitable variety, keep in mind that early potato varieties are most prone to ring rot.
- During the entire growing season, timely identification and removal of diseased plants.
- If you are seriously struggling with ring rot, then it is imperative to observe the crop rotation and not return the potatoes to the same place earlier than after 3 years.
- Before placing the tubers for storage, the tubers must be well dried and heated for 2 weeks at temperatures of at least + 16 ° + 18 ° C to identify infected specimens.
- Mowing and destroying the tops of potatoes one week before harvest reduces the risk of infection.
- Storage treatment with formalin before laying tubers.
- Sprouting seed potatoes in the light will also reveal infected tubers.
Many gardeners successfully fight bacterial and fungal diseases of potatoes, including ring rot, by sowing green manure. The best crops to deal with pathogens are oats, rye, wheat, barley, corn, legumes, tobacco and cabbage. 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, a field intended for planting potatoes should be planted with mustard or oats. Before planting potatoes, the siderates are mowed, the earth is loosened and mixed with plant residues. Saprophytes developing in the soil can significantly slow down 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 pickled fungicides Maxim, Quadris or Gamair biopreparation.
It also makes sense to pickle the tubers with TMTD before planting.
As you can see, if you apply all of the above means and methods in comprehensive protection, then even ring rot of potatoes will not be scary to you.
