Common scab

Common scab of potato is caused by actinomycetes (radiant mushrooms) of the species Streptomyces scabies , as well as several other species of the genus Streptomycetes ( Streptomyces ).

Prevalence

Potato scab is common in all areas of potato growing. The main development factors are weather and soil conditions and the level of agricultural technology .

Maliciousness

If potato is damaged by common scab, the product value of tubers decreases: the taste is deteriorated, the starch content is reduced by 5–30%, the waste from the production of food potatoes is increased, and the tuber's shelf life is reduced.

Damage to the periderm creates favorable conditions for the infection of tubers by other wound pathogens , in particular, pathogens of dry and wet rot .

Pathogen Symptoms and Life Cycle

The pathogen infects the roots, the underground part of the potato stem, penetrates through lentils and wounds in the first weeks of tuber development after planting. On the surface of the tuber, small, shallow ulcers of irregular shape form, which over time increase and cork . Ulcers merge and often form a continuous crust. On freshly dug tubers, a white cobwebby plaque of the mycelium is noticeable, which, when the tuber dries up, dries quickly and disappears.

The tuber pulp morphologically changes slightly.

Disease Development Factors

Tuber infection is prevented by soil antagonist bacteria . However, their protective effect disappears if the tubers remain dry during the first weeks of development. Especially strongly scab is manifested on light sandy and sandy loamy soils, as well as heavily calcareous.

Lime promotes the growth and reproduction of fungi. A neutral or slightly alkaline soil reaction ( pH 6–7.5) is optimal for the development of scab.

Inadequate soil moisture during tuberization also contributes to the development of the disease. High temperature is especially dangerous during the flowering phase of potatoes (the period of mass setting of tubers). The use of unripened manure as a fertilizer causes an increase in the development of common scab. Pathogens accumulate mainly on plant debris after harvesting in the soil. On seed tubers stored under optimal conditions, the infection is almost not saved or is preserved in small quantities.

Control Measures

1. Compliance with crop rotation . Actinomycetes are very resistant to adverse environmental factors and can live in the soil for many years.
2. Sowing siderates into the soil is effective: mustard, lupine, vetch, clover, alfalfa, soy, etc.
3. It is advisable to use physiologically acidic fertilizers ( manganese sulfate or ammonium sulfate at a dose of 60 kg / ha ).
4. Liming of the soil should be carried out in other parts of the crop rotation, since it is necessary to maintain a slightly acidic reaction of the soil.
5. Germination and rejection of diseased tubers
6. It has been established that varieties with a thin or red skin are more susceptible to common scab. Relatively high resistance to common scab are varieties Zhukovsky early, Gatchinsky, good luck and others. Absolutely resistant varieties no
7. A certain decrease in the harmfulness of common scab (up to 40%) can be obtained if tubers are treated with Maxim at a dose of 400 g / t before planting.

The treatment of plants with substances that increase the immune status of plants and are growth regulators (Agat-25K at a dose of 150 g / ha , etc.), to some extent reduce the defeat of tubers scab

1. Planting healthy planting material.
2. Irrigation of the soil should be carried out, starting with the development of tubers (budding-flowering phase) and continuing for a month (it is necessary that the soil moisture in this period of time be at least 75-80% of the total moisture capacity ).

• Potato disease
• Scab (phytopathology)
• Scab of potato