Is it Necessary to Tolerate Scab in the Garden

Scab is a disease that does not include rot. This is a predisposing factor that creates favorable conditions for pathogens of dry and wet rot.

It just seems that scab is a disease that almost does not harm the crop. In quiet years, this is true, because the tubers are well stored in the cellar. Another thing is years with an excess of moisture and a suitable temperature regime: then scab can cause very significant harm.

Black scab

Scab is especially raging if spring is rainy and cold. The gardener may lose a quarter of the expected harvest. There are several forms in which this manifests itself. Possible rotting of buds and shoots, dying of roots and stolons, necrosis of tubers…

Signs of black potato scab

If small lumps of earth stick to the skin of the tuber, but they cannot be shaken off or brushed off with a gloved hand, they cannot be erased, but they can be knocked down with a fingernail or scraped together with the area of skin on which they sit – this is a black scab.

If the weather is warm, sprouts from diseased tubers may appear from the soil, even grow into a bush, but the encircling edges will be visible, twisted along the veins of the upper leaves, sometimes with anthocyanin color. Small green aerial tubers may appear in the axils of the shoots. The bushes will be small. If the weather becomes warm, with high humidity, then a white film-like coating will appear on the lower parts of the shoots.

The collage photos show the manifestations of black scab on the trunks, tubers, upper leaves

The time of tying the tubers (in hot weather — the time of flowering) is the period of the appearance of the mesh on the skin, as the tubers grow, the skin bursts in these places.

What harm does black scab do

There is almost no harm to the tuber, because the formations are superficial. The fungus is activated in the spring, when planted in cold, moist ground, in the same cold and humid weather. Mycelium gets on the sprouts, depressed dark spots form on them, which gradually grow, forming a ring around the embryo.

The affected sprouts die without even emerging from the soil. For a gardener, it may look like a simple bald spot in a row. If there were a lot of tubers with black specks when planting, then some of the bushes simply will not appear. Therefore, it is not necessary to plant potatoes in cold soil, and even bury the tubers deeply. Apparently, it is not for nothing that our ancestors believed that the best time for planting potatoes is determined by the temperature of the soil – bare feet should be comfortable. This fungus also affects beets, pumpkins, tomatoes.

Is it possible to reduce the damage

In autumn and spring, ventilate seed potatoes, plant only healthy sprouted tubers.

Common scab

Usually gardeners and gardeners believe that this potato disease does not do much harm. Perhaps the most unpleasant manifestation of it is the ugly skin of tubers. Well, it’s not scary, because the beds are grown for your table, not for sale. However, this is not quite right.

The damage can be very impressive, judge for yourself: in different regions, ordinary scab can affect more than half of all tubers, germination can decrease by 15%, up to a third of the crop is lost, and the tubers themselves become tasteless, because there is less starch (it depends on the looseness) and protein in them. Scab pathogens need to “eat”, and starch and protein are very high-quality food for it.

Signs of potato scab

Accomplices of ordinary scab, pathogens of dry and wet rot, penetrate into the affected tubers through “wounds”. Various wet spots, ulcers that peel off.

What harm does ordinary scab do

Ordinary scab is an underground inhabitant, it parasitizes only on stolons and tubers. Pathogens – radiant fungi actinomycetes, penetrate only into young tubers during their formation, when tiny ruptures of skin tissues are possible, when lentils are actively working, because the nodules are actively growing. At first, the development is invisible to the gardener, if he digs a hole, he is unlikely to see it, because sometimes only by the end of the second month brown spots on the skin become visible. The colonization of tubers by pathogenic microorganisms can take up to thirty days.

Common scab forms

Scab is a surface disease. It can be in four forms, which differ in appearance:

• convex scab:first, the skin of the tubers appears in the recess in the form of a cone, then they rise, take the form of small warts or scabs up to 2 mm;
• flat scab: the skin hardens, changes color from light brown to dark, ulcers in scabs form on the skin;

This scab so disfigures the surface of the tuber, opens passages for pathogens of fungal diseases

• mesh scab: across a hard, coarse scab crust from grooves running in different directions;
• pitted (deep) scab: ulcers are formed with a depth of 5 mm, their diameter can be very large (compared to the size of the tuber), the skin around them is torn. The inner part of the ulcer is loose and soft.

Is it possible to reduce the damage

Ordinary scab likes alkaline soil, so do not overdo it with deoxidation. If you choose a plot for potatoes, then three or four years before growing, it is not necessary to add lime for deoxidation, it is better to do this for the predecessors. Soil bacteria fight well with pathogens of common scab. But the soil should be moist, not dry, when potatoes tie tubers, otherwise the protection will not work. Ordinary scab likes warm soil, with a low humus content (humus is able to restrain its onslaught). It develops only in the field and calms down during storage.

The seed material is almost not stored in the cellar, it is not transmitted from tuber to tuber. They are more susceptible to scab:

• tubers with thin skin;
• varieties with red skin;
• early potato varieties.

Powdery scab

You may lose more than half of the possible harvest. Against the background of scab (through ulcers on the surface), tubers may develop a black leg. For the development of the disease, increased soil moisture is required, only under this condition are pathogenic microorganisms able to penetrate the cells. Scab parasitizes all underground organs, plants can die from damage.

Signs of powdery scab potato

A month after planting, small brown spots and brown streaks appear on the tubers. In place of the spots, convex pustules appear, similar in structure to jelly, their diameter is no more than 4 mm (0.15 in), they grow to a diameter of 1 cm (0.4 in), and then darken and dry up.

Damage to potato tubers by powdery scab

If the stolons, stems, roots are affected, white growths are visible — it looks like cancer.

Is it possible to reduce the damage

Process the tubers before planting. Plant in agronomic conditions, in warm soil, preferably not heavy and not acidic. If cows were fed sick tubers, then fungal spores will appear in the manure, this is another source of infection.

Silver scab

There are no shoots, because the eyes of the tubers are dying. Or they are changed: weak, thread-like, they are smaller than is usually the case with healthy tubers, and the length is shorter. These potato bushes are stunted because of their neighbors. Tubers are ugly or do not reach the size that guarantees the description of the variety, because stolons are affected.

Here’s what a silvery scab looks like on tubers with a white skin

Signs of silver potato scab

All the underground organs of the plant are sick, especially the tubers, which are charged during the entire growing period. The autumn disease is hardly noticeable: at this time you can see the characteristic silvery sheen of scab – spots of light brown color, try to understand what is hidden there on the yellow peel under the remnants of the soil. It can be determined visually during storage – about a month and a half after the bookmark. The tubers acquire all the “beauty” by spring: then a metallic silvery sheen appears, especially noticeable if the potatoes are simply soaked with water.

Is it possible to reduce the damage

Mycelium lives only in the cells of the skin, which changes its color from light brown to dark brown. Because you need double etching: in autumn, before laying seed tubers for storage, and in spring, before planting. Cutting the tops before harvesting allows the tubers to form a dense peel, which makes them resistant to the disease. Grow wheat as a precursor to potatoes, do not spare humus or other organic matter for fertilizer, this increases the number of microorganisms in the soil and increases its acidity.

Lumpy scab

The pathogen harms the eyes of seed potatoes, reduces the content of starch, protein and vitamin C. Weakened tubers are easily damaged by black and silver scab, rot. The disease can be determined after three to four months of storage of tubers. Due to damage to the eyes, germination decreases, and some sprouts that have sprung up are already affected by the disease.

Signs of lumpy scab potatoes

Infection occurs in the soil during the formation of tubers. But it can only appear during storage, about two or even four months after planting. On the surface of the tubers, closed skin tubercles with a diameter of about 5 mm (0.2 in) are formed near the eyes and lentils. A ring formed by cells closed around them. Depending on the potato variety, the tubercles can be of different shapes, single or multiple, merging into one structure.

It looks like a lumpy scab on potato tubers

Later they turn into pustules, the edges of which are pressed into the pulp of the tuber, and the central part rises above the surface. Outside, the pustules are dark brown, and if the tuber is moistened with water, then inside their color will change to gray-purple, because there is rot.

Is it possible to reduce the damage

Observe the crop rotation, dry the seed tubers before laying for storage. Ventilate the basement so that it is not too wet.

And how do you fight potato scab? Or do you let her freely manage your harvest?

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