Potato scab and methods of dealing with it

Potato scab among gardeners is often mistakenly considered the most harmless disease. She has no initial external signs of the development of the disease. Some varieties of potato scab do not manifest themselves in the initial stage. The whole danger of the disease lies in the fact that the infection accumulates in the soil and year after year reduces the quantitative indicators of the potato harvest.

Potato scab and methods of dealing with it

Types of scab

The causative agents of potato scab are fungi and, depending on their type, several varieties of fungal disease of vegetable culture are distinguished:

• ordinary,
• black, or rhizoctonia,
• powdery,
• silvery.

Causes of infection

Among the main reasons contributing to the appearance of the fungus:

• getting the scab fungus on healthy potato tubers from contaminated soil,
• acquisition of infected planting root crops,
• violation of crop rotation and planting a vegetable crop in the same planting place,
• exceeding the norm for the content of nitrogen component in the ground ,
• increase in soil temperature above 20 ° С,
• low acidity of the soil layer,
• non-compliance with the rules for fertilizing the soil about by manic manure and compost.

Harm from scab

Scab on potatoes does not pose a risk to human health, however vegetables that can be eaten lose their nutritional value: compared to healthy tubers, the starch content in them is reduced by 2 times.

Affected potato tubers are poorly preserved due to the intensive development of rot in them. The infected root crops preserved during the winter period cannot be used as planting stock. They are forbidden to land in the ground, as they act as sources of soil contamination. As a result, an unhealthy potato crop will be obtained, and a fungus will settle in the soil.

Common potato scab

Common scab is a fungal infection often found on potato beds.Its causative agent of fungal origin Streptomyces scabies prefers to settle in a dry sandy soil layer with a low to medium acidity level and activates its activity at temperatures ranging from 25 ° C to 28 ° C.

Symptoms

Among the main features characteristic of an ordinary potato scab:

• small brown lesions, sometimes with shades of red or purple,
• rough surface of potato tubers ,
• the appearance of slightly noticeable mesh grooves on the nematode.

In cases of severe infection of potato tubers, the lesion foci increase in size and subsequently begin to harden and crack. The result of the process is rotting vegetables.

Distribution

An ordinary variety of fungus practically does not damage other parts of the potato bush, spreading mainly through the tubers. During storage at low temperatures in the basement, the common scab fungus falls into anabiotic state, but does not die, which saves the harvested and stored crops until spring.

Most susceptible to the ordinary variety are potato varieties with thin red peeled.

Contributing factors for the development of the fungus are:

• insufficient watering
• fertilizing the land with raw, not yet rotted manure,
• excessive limestone.

Prevention and treatment

You can fight the scab

Against an ordinary scab on potatoes, they treat the land intended for planting vegetables. In addition, gardeners try to plant fungus-resistant varieties, which include Kamerz, Domodedovo, Yantarny, Priekulsky, Zarechny.

As a preventative measure, how to deal with scab on potatoes, it is recommended to spray planting tubers with drugs such as polycarbacin either nitrafen. An effective method of prevention for the development of immunity against fungus will be the germination of seedlings in sunlight. Potato seedlings should be watered immediately after it has been planted in the ground and watering should be completed when the stem reaches a width of 1.5-2.0 cm.

Powdered potato scab

In contrast from an ordinary fungus species that prefers dry land, powdery scab is a consequence of the action of the pathogen Spongospora subterranean. The fungus settles in waterlogged soil and is able to maintain its activity for up to five years.The optimal conditions for its occurrence are considered to be temperature limits from 10 ° C to 12 ° C.

Symptoms

Among the main external symptoms of the description of the disease characteristic of the powdery variety:

• covering the stems with white growths,
• the appearance on the potato roots of multiple red-brown wart neoplasms of different sizes.

Distribution

Powdery scab affects both tubers and plant stems, mainly their lower part. fungal pathogens are transmitted through organic residues preserved in the soil, but can also be spread by air. Damaged tubers usually dry out during storage, but begin to rot when the humidity is high.

Rains contribute to the spread of the powdery form of the disease.

Prevention and treatment

Potato varieties Cardinal, Majestic, Yubel are resistant to this type of fungal disease. In order to prevent powder fungus, gardeners often withstand grown seedlings before planting in soil in formalin solution for 5-7 minutes, subsequently covering them with tarpaulin for several hours.

Black potato scab

The causative agent of black potato scab is the fungus Rhizoctonia solani, which is activated at a temperature of 16 ° C to 18 ° C.He prefers high humidity, the indicators of which are about 80-100%. A fungus develops in loamy soil.

Symptoms

The main signs of the defeat of a vegetable crop in the black variety are black or dark brown spots of the lesion that appear on the surface of the root crops. Over time, they merge into vast foci. Often, inexperienced gardeners take the black form of a fungal disease for soil dirt. Infected seedlings develop with twisted leaves.

Spread

The disease can ruin the entire crop

Black scab of potato, or rhizoctonia, is the most dangerous form, affecting the entire potato bush. From the black variety of fungal disease, tubers, stems and foliage of potatoes suffer. The fungus develops with rapid intensity, is able to penetrate into the potato tubers already at the germination stage, condemning the future crop to death.

Among the factors contributing to the spread of the disease is a cold rainy season in late spring time.

Treatment and prevention

Varieties resistant to the black variety have not been bred. Given the serious damage from this fungal disease, chemicals are often used to combat it.As a prevention, gardeners use the treatment of tubers with the help of Integral, Vitavax or Bactofit. As an agrotechnical measure, it is recommended to plant a vegetable crop to a depth of not more than 7 cm in sandy loam soil, not deeper than 12 cm in peat and not more than 11 cm in loamy soil. A preventive measure will be landing in a ground warmed up to at least 8 ° C. Organic fertilizers and amounts exceeding the usual norm help to prevent the black variety of the disease. Gardeners’ reviews recommend using copper sulfate, which needs to spray bushes in the fight against the black variety of fungal disease.

Silver potato scab

The causative agent of the silver variety is the fungus Helminthosporium solani, which is capable of maintain their vitality at temperatures falling to 3 ° C. The fungus settles on any soil – loamy or sandy loam, when the humidity reaches a level of 80-100%.

Signs

Among the main external signs of silver scab of potato stains on potato tubers with a silver tint, occupying up to 40% of the root surface. Initially, the foci of black soot are peeling off, turning gray, and the affected vegetables begin to dry out and wrinkle, decreasing in size.

Distribution

The fungal disease spreads to the flowering stage of the vegetable crop and with the formation of root crops.The potato silvery scab that retains its activity even at low temperatures during storage affects healthy tubers, leading to losses of the harvested crop of up to 40%.

Treatment and prevention

Preventive treatment of harvested tubers potatoes are carried out using chemical treatment of vegetables before storing them with Nitrafen or Botran.

General control measures

Each of the considered varieties of fungal disease has its own pathogen, however, in the fight against they apply general Prevention and treatment measures.

Agriculture

Among the methods of how to deal with scab on potatoes and get rid of it, the central place among all methods is the correct crop rotation, which suggests that a vegetable crop changes its planting site annually, and on a land infected with fungus, vegetables do not plant for at least 4-5 years. This period is enough for the fungus to die. It is forbidden to grow other crops susceptible to fungal disease, carrots, peppers, tomatoes, eggplants, and beets on contaminated land. Gardeners achieve positive results by alternating different varieties of potato plantings with onions or legumes.

Outbreaks of the disease are caused by fresh manure introduced into the soil.

As a measure of treating infected land, green manure is used, among which legumes, cereals and mustard help to treat the soil most often. Siderates that reach a height of 10-15 cm are digged along with the ground. The remaining siderates in it will become a source of saprophytic fungi and bacteria, which are the natural enemies of scab fungi, which helps to cure infected soil.

Fertilizers

Scab, especially an ordinary variety, develops in alkaline soil, therefore, fertilizing the earth with manganese and boron before planting potatoes will become a barrier to the development of fungal disease. For 100 sq.m, the fertilizer rate will be:

• ammonium sulfate – 1.5 kg,
• superphosphate – 2.0 kg,
• calimagnesia – from 2, 5 to 3.0kg,
• copper sulfate – 40g,
• manganese – 20g,
• boric acid – 20g.

Drugs

Treatment and prophylaxis measures are directly related to the treatment of the vegetable culture with fungicides. Etching vegetables is recommended before planting the tubers. Most often, gardeners also use help against phytophthora Maxim, Fito plus and Fitosporin. The last fungicide can be used to process seed potatoes and bushes planted in the ground at least 3 times during the growing season.

Less common chemical measures can be used against the common variety. It is enough to treat the tubers before planting with a growth regulator, for example, Zircon.

To get rid of the fungus on the potatoes, the stronger Phenorams, Mancozeb, help. Their use is carried out before landing.