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Video: How To Protect Potatoes From Common Scab
Scab - features of the manifestation of the disease and how to prevent it
Common scab is considered one of the serious diseases of potatoes. It is widespread everywhere where this crop is grown, and is characterized by high harmfulness. The tubers affected by scab have an unattractive appearance, reduced taste and marketability, and the keeping quality of potatoes greatly deteriorates during the winter storage period.
Affected tubers rot much faster, as other phytopathogenic microorganisms - fungi and bacteria - settle in the affected areas. Seed material, in which the surface of the tubers is severely scab, is unsuitable for planting, because, as a rule, it has a reduced germination rate (up to 10%) and gives a decrease in yield (up to 30%). Especially serious crop losses from this disease are observed in years with dry and hot summers (especially on sandy soils). The market value of ware potatoes is also significantly reduced: when cleaning tubers, a large waste of products is obtained.
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Common scab is caused by a number of species of soil streptomycetes (radiant fungi), which are highly resistant to drought and are able to start developing even at 20% soil moisture. Scab spores successfully tolerate dehydration and low temperatures (down to -30 ° C). Infection of tubers with these fungi begins when their peel is not fully formed: from the beginning of tuberization within 10-30 days (depending on the variety and environmental conditions).
On the surface of the infected tuber, shallow ulcers of a round shape (with a diameter of 2-3 mm to 10-12 mm) appear. Often these ulcers coalesce and form a solid crust that covers the entire surface of the tuber. The scab pathogen also affects stolons and roots.
There are four forms of manifestation of this disease (convex, flat, mesh and deep).
Convex scab appears first in the form of small cone-shaped depressions. Later, the depressions rise above the surface of the tuber, forming wart-like or scab-like growths up to 2 mm high.
Flat scab is more common on young tubers and is characterized by a brownish hardening of the rind or abrasions (scabs) on the surface of the tubers that are reddish brown and then dark brown.
Features of the reticulated scab are solid roughness, surface scab in the form of shallow grooves intersecting in different directions.
Pitted (deep) scab is characterized by the formation of brown ulcers 5 mm deep and up to 100 mm in size, surrounded by a torn skin. Ulcers can take many forms. Their inner surface remains soft and loose for a long time.
There is also a convex-deep scab - a combined formation of a convex and deep scab on the same tuber. In this case, more or less deep ulcers sometimes appear on the wart-like growths.
The causative agent of the disease is introduced into the tubers through the lentils, which, growing, tear the peel in different directions (in some cases, in the form of asterisks). External conditions have a serious impact on infection with a pathogen: humidity, temperature and soil acidity). The maximum damage to tubers is noted when soil moisture is 50-70% (of its full moisture capacity), which is equally optimal for both the causative agent of the disease and the potato itself.
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Scab develops on soils with weak acidity more intensively than on acidic soils. But due to the variability of the population in recent years, the pathogen also actively behaves on soils characterized by high acidity. The main sources of infection for common scab are soil and highly infected planting material. An increase in the defeat of tubers is also observed if there are undecomposed plant residues and fresh organic matter in the soil.
Reducing the harmfulness of scab can be achieved if fertilizers containing boron, manganese and other trace elements are applied under the potatoes. It is noted that an excess of free potassium and nitrites enhances the manifestation of scab. Severe damage to plant material by scab is possible with permanent potato culture, when high doses of lime are introduced into the soil.
On household plots with good air permeability (for example, on light sandy ones), where a strong manifestation of common scab is observed, it is advisable to cultivate resistant varieties. Although there are no completely unreceptive potato varieties in the global assortment yet. This is due to the constant presence in the soil of several types of radiant fungi that cause scab and differ in their biological characteristics, as well as the fact that their composition changes from year to year.
Of the varieties of the Research Institute of Potato Farming, Kalinka, Udacha, Ramensky, Vestnik, Zhukovsky early, Ilyinsky, Nikulinsky and Bezhetsky show good resistance to this disease. The varieties of the Belarusian (Veras and Naroch) and northwestern (Oredezhsky, Nayada, Zagadka) selection are relatively resistant. The varieties Snegir and Lark, popular among our gardeners, exhibit medium resistance to common scab.
To reduce the damage to tubers by this pathogen, it is necessary to provide the potatoes with favorable predecessors. The best of these are considered winter cereals (eg rye), lupine and legume-cereal mixtures, clean and busy fallow. Experts do not recommend fertilizing the soil for potatoes with fresh straw manure directly in the spring: this stimulates the development of scab (it is advisable to apply organic matter under the predecessor). It is possible to reduce the harmfulness of the disease by introducing acidic forms of nitrogen and phosphorus fertilizers into the rows when planting potatoes (at the rate of kg / weaving: ammonium sulfate - 1-1.5 and superphosphate - 1). Lime is recommended to be used in conjunction with organic fertilizers.
Watering potato bushes (4-6 weeks), starting from flowering (from tuberization) of plants, is an effective means of reducing the manifestations of common scab. Since the mycelium of the pathogen is able to spread from diseased tubers to healthy ones, the planting is carried out with tubers clean from scab.
Unfortunately, for the private sector there are still no sufficiently effective and at the same time safe drugs (permitted by the state "List of Chemicals …") that would destroy or significantly reduce the superficial infection of common scab.