What is potato late blight: description of the disease and treatment methods

Potato late blight is a dangerous fungal disease that is difficult to treat due to the ability of the pathogen to develop resistance to fungicides. Farmers focus their main efforts in the fight against late blight on preventive measures, including pre-planting seed treatment, selection of varieties resistant to the fungus, and spraying with copper-containing preparations.

In this article we will talk about potato late blight with a description of the disease and treatment methods.

What is late blight

Late blight is a disease caused by the late blight fungus. Mycelial lower organisms lead a parasitic way of life, destroying plant tissue.

Historical reference. In 1845-1849, the fungus Phytophthora infestans caused a significant spread of late blight, which led to the Great Famine in Ireland.

The photo shows potatoes affected by late blight.

Description and characteristics of the disease

The disease was first discovered practically simultaneously in the USA and Europe in 1842-1843. Presumably, late blight was brought from Peru during the export of Chilean saltpeter in the early 1840s. The German scientist de Bary, who described the pathogen, called it “phytophthora,” which literally means “plant eater.”

Potato plantings are affected by the fungus Phytophthora infestans Mont. de Bary, named after that same scientist.The pathogen is activated from late May to August and spreads with lightning speed under conditions of high air and soil humidity, sudden changes in day and night temperatures, morning dew and fog. Simply put, wet and cool weather is the optimal environment for the development of late blight. In the southern regions it spreads to abundantly irrigated areas.

Potatoes suffer from late blight of tops and tubers. Damage to greenery is observed on 20-50% of plantings, and on tubers - on 8-23%. Crop losses are 30-50%.

Late blight, introduced to Europe in the 19th century, was the only causative agent of the disease of the same name until the 80s of the 20th century. In Switzerland and other European countries, a new genotype of the fungus was discovered - A2, which differs from the previous ones in aggressiveness and the ability to easily adapt to unfavorable conditions.

As a result of the joint development of both forms, new sexual structures - oospores - were formed. They have a thick two-layer shell, remain viable for a long period in low temperature conditions, and overwinter on tubers, tops remains and in the ground.

The disease began to be detected on stems 1-4 weeks earlier than usual, and the level of infection of tubers increased.

Reference. With the appearance of the A2 form of the fungus, the disease is diagnosed in the germination phase. Oospores remain viable for 4 years, accumulate in the soil and, under favorable conditions, cause an outbreak of the disease.

Signs of potato late blight

Signs of leaf blight:

• brown spots on the lower leaves;
• white plaque is the result of the vital activity of the fungus, which accurately identifies the disease;
• dry leaves;
• longitudinal brown stripes on stems.

Humid and warm weather contributes to the intensive spread of late blight.In just 3-5 days, the greens turn into a dark, rotten mass. During drought, the development of the fungus stops, the spots dry out, and the leaves become brittle. If the fungus spreads extensively, the plant dies.

Late blight quickly passes from a diseased bush to a healthy one, forming new foci of the disease.

Signs of tuber blight:

• hard depressed gray-brown spots on the surface;
• rusty-brown uneven necrosis on the pulp;
• wet or dry rot on potatoes.

Reference. Spores germinate in drops of water or dew at an air temperature of +4...+30°C and are carried by air currents.

Causes of infection

The development cycle of late blight occurs in two ways: the infection develops on the sprouts of infected seeds or on potatoes rejected after digging. After the initial infection of the bushes on the site, several repeated waves of infection occur, which directly depend on weather conditions.

Infection occurs during the harvesting process - when tubers come into contact with potato tops. In the storage facility, the infectious cycle closes.

Fighting methods

To combat potato late blight, treatment with chemicals and folk remedies is used.

Traditional methods

How to fight late blight on potatoes using folk remedies?

Gardeners use the following medicinal solutions:

1. Dilute whey or milk with 1% fat content with water in a 1:1 ratio. Use the solution for spraying bushes, starting in July, every 2-3 days. To enhance the effect, add 15 drops of iodine per 1 liter of liquid.
2. Dissolve a pack of “live” yeast (100 g) in 10 liters of water. Treat plants at the first signs of late blight 2 times a week.
3. Pass 200 g of garlic arrows through a meat grinder, pour 200 ml of warm glass of water and leave for 24 hours.Strain the infusion and dilute with 10 liters of water. Add 1 g of potassium permanganate to the liquid. Spray the plantings every 10 days.
4. Pour 1 kg of nettle and wormwood into 10 liters of water and leave for 24 hours. Then strain and add 50 g of soap shavings. Spray greenery once every 10-12 days.
5. Before flowering, treat the bushes with a solution of copper sulfate (2 tablespoons of powder per 10 liters of water).
6. Mix 1 liter can of wood ash with 200 g of tar soap shavings and add 10 liters of water. Processing can be carried out at any time.
7. Mullein infusion 1 liter, pour 10 liters of water, leave for 1 hour. Spray plants before flowering.
8. Chop 100 g of dried tinder fungus with a sharp knife, place in a non-metallic container and pour 1 liter of boiling water. Leave until completely cool, strain and apply to treat potato plantings once every 10 days.

Natural-based products are safe for plants, humans, birds and bees. Combined use and rotation increases their effectiveness and prevents crop loss.

Chemicals

The most effective are combination drugs containing systemic and contact substances. Treatment with them makes it possible to stop the development of the fungus for 20-30 days and reduce crop losses.

The first and second preventive sprayings with combined agents are carried out at the stage of closing the tops in the rows, without waiting for the first symptoms to appear.

In case of early manifestation of the disease, systemic drugs are first used, then the bushes are sprayed with contact agents according to the following scheme:

• systemic chemicals: “Ridomil Gold”, “Quadris”, “Thanos”, “Infinito”, “Tattu”, “Ordan”, “Acrobat MC” - every 10-12 days;
• contact: “Antrakol”, “Azofos”, “Ditan”, “Zummer” - every 7-8 days.

In humid and warm weather, the interval between treatments is reduced to 5 days.

A week before harvest, spraying is stopped, potato tops are cut off and completely removed from the site. When the above-ground part is collected late, fungus accumulates and mass infection of tubers occurs.

Potato digging is carried out in dry weather. When forced to harvest in rainy weather, the tubers are stored under a canopy or in ventilated bays. Over the course of 2-3 weeks, the potatoes are sorted, damaged and diseased specimens are discarded and transferred to storage.

"Epin"

"Epin" is an analogue of a natural plant growth stimulator that has an anti-stress effect. It increases the protective forces and productivity of plants, stimulates the development of roots and stolons, accelerates the ripening of potatoes, and reduces the amount of nitrates and pesticides. The product is used for spraying green mass and soaking seeds before planting.

Reference. Due to widespread counterfeiting, the drug Epin was discontinued in 2003, but was replaced by Epin-Extra with a greater degree of protection against counterfeiting.

The drug contains the synthesized substance epibrassinolide, which is responsible for accelerating biological processes in plants and increasing stress resistance.

The product is produced in ampoules of 0.25 mg and is used strictly according to the instructions, avoiding overdose. The solution is thoroughly mixed and used on the day of preparation. It is advisable to add citric acid to the tap water at the tip of a knife - the alkali it contains reduces the effect of the active substance.

The table shows the scheme for using Epin.

Spraying of potato bushes is carried out in the morning or evening due to a decrease in the activity of the active substance under direct sunlight. The leaves are sprayed on both sides. In stressful conditions - drought, light deficiency, the first signs of late blight - treatment is carried out once a week until complete recovery. Preventive spraying is recommended 3 times a season.

"HOM"

"HOM" is a copper-containing fungicide to combat late blight, containing copper oxychloride (861 g/kg). Analogues - “Oxychom”, “Polychom”, “Bordeaux mixture”.

Potatoes are processed during the growing season. To prepare a working solution, take 40 g of the substance per 10 liters of water. Consumption per 100 sq. m - 6–8 l. Number of treatments - 5, validity period - 28-30 days.

The solution is poured into a spray bottle and the leaves are sprayed from above and below in the morning or evening.

"Trichopolus"

«Trichopolum» is a pharmaceutical antimicrobial and antiprotozoal drug containing metronidazole. The active component affects DNA cells, causing the death of microorganisms.

Experienced gardeners advise using the drug together with a 1% solution of brilliant green, which heals wounds on the leaves, stopping the development of late blight.

Reference. "Trichopol" with brilliant green is used only for preventive purposes and in the early stages of the disease. The product is ineffective as a treatment for massive plant infestation.

Solution recipe:

• 10 tablets of "Trichopol";
• 35-40 drops of brilliant green;
• 10 liters of water.

Grind the tablets into powder, pour into water and add brilliant green. Mix thoroughly, pour into a container and treat the bushes with a sprayer. Treatment frequency: once every two weeks, every 10 days.

Prevention measures

Prevention of potato late blight includes:

• breeding resistant varieties;
• selection of healthy seed material;
• disinfection of tubers with fungicides before planting;
• heating and germination of seeds;
• re-sorting of potatoes after germination (at a temperature of +15...+17°C, even the smallest spots of late blight grow within 15-25 days);
• disposal of potato residues after spring sorting;
• crop rotation;
• planting potatoes away from tomatoes, eggplants and peppers;
• application of balanced organic and mineral fertilizers.

Read also:

How to fight late blight on tomatoes in a greenhouse using traditional methods.

How to deal with late blight on tomatoes: best methods and practical tips.

Potato varieties resistant to late blight

The table contains varieties resistant to late blight.

Is it possible to eat potatoes affected by late blight?

Potatoes with signs of late blight are safe for humans.You can eat it, but you must first cut off the rotten parts on the potatoes.

Reference. Heat treatment completely kills fungal spores.

Conclusion

Gardeners know first-hand about potato late blight. This is one of the most common diseases, the fight against which often lasts the entire season. The danger of late blight lies in the lightning-fast spread of fungal spores by the wind. High humidity and high air temperatures are an ideal environment for the development of late blight.

Work to prevent the disease is aimed at disinfecting tubers before planting, treating them with growth stimulants to increase immunity, and preparations with copper “Hom”, “Oxychom”. To treat the plant, fungicides are used: Ridomil Gold, Quadris, Thanos, Infinito, Tattu, Ordan, Acrobat MC, Azofos, Ditan.