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Diseases of vegetable crops, in general, are an unpleasant thing, and when there are no special pesticides to combat 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 destroy up to half or more of the annual harvest.
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 photos of signs of the disease, as well as its description and treatment methods. You just need to immediately understand that in the case of ring rot, treatment as such is usually not carried out. Infected plants must be immediately destroyed - they cannot be saved. But disease prevention plays a very important role.
Signs of ring rot disease
The causative agent of ring rot is bacteria of the species Clavibacter michiganensis subsp. sepedonicum or otherwise they are called Corynebacterium sepedonicum. They belong to a type of aerobic bacteria.
Signs of the disease appear on 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 noticed when they are cut, so if the tubers are already sitting in the ground, then the disease can only be tracked by the above-ground part of the potato bush.
One or two stems in the bush wither, and they quickly fall to the ground. This fall is already a characteristic sign of ring rot, since with other diseases (verticillium, fusarium), wilted stems remain standing. Then brown spots appear on the tips of the leaves of the wilted stems. Sometimes the leaves of affected stems may turn white due to loss of chlorophyll.
The fact is that bacteria, moving from the infected tuber along the stolons to the stems of the 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 that are toxic to potatoes.
As a result of significant damage by ring rot, the following symptoms are observed:
- The upper leaves of the entire bush begin turn yellow and curl up.
- The surface between the veins of the leaf acquires a fawn color, so the leaves become speckled.
- The lower leaves of the bushes become limp and thin, their edges may curl upward.
- The internodes are shortened, and the potato bushes take on a dwarf appearance.
All these symptoms are well illustrated by the photographs below.
If you cut off a diseased stem and place it in water, light yellow mucus will clearly ooze 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 roots is destroyed.
Potato tubers, still slightly affected by infection, are practically no different 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 potato tissue. In the photo below you can see what potato ring rot looks like on a tuber in the initial phase of infection.
As the disease progresses, the vascular system of the potato begins to completely collapse and turns into a slimy mass that 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 the autumn during harvest. At first, it is impossible to notice any signs of 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 skin, where the infection occurred, light spots no larger than 2-3 mm in size form. Subsequently, they begin to increase and reach 1.5 cm. The pulp in these places begins to decompose and a hole 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.
Infection with ring rot usually occurs from old tubers, through stolons, and symptoms in the form of necrosis of the vascular ring appear 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 as best as possible the sources of infection and the conditions for the development of the disease in order to understand what preventive measures should be taken to protect yourself as much as possible 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 dry conditions, the development of the disease stops, and although the above-ground part of the plants quickly withers, this has practically no effect on the tubers. They look quite healthy.
The main source of infection persistence and transmission to new generation tubers is already affected tubers. Unlike some other pathogens, ring rot bacteria do not persist in the soil and do not overwinter. But they can easily survive 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 for their intended purpose as soon as possible.
The infection is also easily transmitted through tools when harvesting potatoes and especially when cutting tubers.
It can be even more difficult to combat the disease, because its causative agent is quite capable of moving from tuber to tuber over several generations without any special visible symptoms, if suitable conditions for its development do not occur. Therefore, sometimes it turns out that planting apparently healthy tubers can result in 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 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 crop rotation and not return potatoes to the same place earlier than after 3 years.
- Before storing tubers, they must be thoroughly dried and heated for 2 weeks at temperatures of at least +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 formaldehyde before planting tubers.
- Germinating seed potatoes in the light also makes it possible to identify infected tubers.
Many gardeners successfully fight bacterial and fungal diseases of potatoes, including ring rot, by sowing green manure.The best crops to cope with pathogenic organisms are oats, rye, wheat, barley, corn, legumes, tobacco and cabbage. It is necessary to select fast-growing crops that are capable of producing a sufficient amount of green mass from harvesting potatoes to frost. In early spring, a field intended for planting potatoes must be planted with mustard or oats. Before planting potatoes, green manure is mowed, the soil is loosened and mixed with plant residues. Saprophytes developing in the soil can significantly inhibit the development of bacteria.
Finally, you can try to use some ready-made drugs to combat this disease. Seed potatoes can be treated both before planting and before storing fungicides Maxim, Quadris or the biological product Gamair.
Before planting, it also makes sense to treat the tubers with TMTD.
As you can see, if you use all of the above means and methods in comprehensive protection, then even ring rot of potatoes will not be scary for you.
