Blight disease tomatoes

Early blight in tomato and potato

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Quick facts

• Early blight is one of the most common tomato and potato diseases, occurring nearly every season in Minnesota.
• It affects leaves, fruits and stems and can be severely yield-limiting when susceptible tomato cultivars are used and weather is favorable.
• Severe defoliation can occur.  In tomatoes, fruit can be damaged by sun.

Identification

• Initially, small dark spots form on older foliage near the ground. Leaf spots are round, brown and can grow up to 1/2 inch in diameter.
• Larger spots have target-like concentric rings. The tissue around spots often turns yellow.
• Severely infected leaves turn brown and fall off, or dead, dried leaves may cling to the stem.
• Seedling stems are infected at or just above the soil line. The stem turns brown, sunken and dry (collar rot). If the infection girdles the stem, the seedling wilts and dies.
• Stem infections on older plants are oval to irregular, dry brown areas with dark brown concentric rings.
• Fruit can be infected at any stage of maturity.
• Fruit spots are leathery and black, with raised concentric ridges. They generally occur near the stem. Infected fruit may drop from the plant.

Biology

• Early blight can be caused by two closely related species: Alternaria tomatophila and Alternaria solani.
• Both pathogens can infect tomatoes, potatoes, peppers, and several weeds in the Solanaceae family including black nightshade (Solanum ptycanthum), and hairy nightshade (Solanum physalifolium)
• Disease develops at moderate to warm (59 to 80 F) temperatures; 82 to 86 F is its optimum temperature range
• The pathogen is most likely to spread with any weather or heavy dew, or when relative humidity is 90% or greater
• The early blight pathogens both overwinter in infected plant debris and soil in Minnesota. The pathogen also survives on tomato seed or may be introduced on tomato transplants.
• Lower leaves become infected when they come into contact with contaminated soil, either through direct contact or when raindrops splash soil onto the leaves.
  • Spores (reproductive structures) can germinate between 47° and 90° F and need free water or relative humidity of 90% or greater.
  • Spores infect plants and form leaf spots as small as 1/8 inch diameter in as little as five days.
• Spores can be spread throughout a field by wind, human contact or equipment, resulting in many reinfection opportunities throughout a growing season.

Managing early blight in the home garden

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Managing early blight on farms

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CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Be sure that the plant you wish to treat is listed on the label of the pesticide you intend to use. And observe the number of days between pesticide application and when you can harvest your crop. Remember, the label is the law.

Marissa Schuh, horticulture IPM Extension educator, and Michelle Grabowski

Reviewed by Natalie Hoidal, Extension educator

Reviewed in 2022

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Late blight of tomatoes. Prevention and control measures - Botanichka

In recent decades, an unpleasant disease called "late blight" has become the scourge of our gardens. When you encounter it for the first time, you catch yourself thinking: is it worth it to grow tomatoes at all, if so many efforts are so simple, they come to zero. However, late blight, or late blight, is still not the worst thing that can happen to our beds. With knowledge of the characteristics of the disease, it can be prevented by saving oneself from grief and disappointment.

Contents:

• Signs of tomato late blight
• What contributes to the development of late blight?
• Preventive measures against late blight
• Late blight control chemicals
• Microbiological agents
• Folk remedies against late blight

Signs of tomato late blight

Late blight or brown rot of tomatoes is a fungal disease caused by the protozoan microscopic fungus Phytophthora infestans. It manifests itself in the form of elongated dark brown spots or stripes on the stems and petioles of plants, grayish-brown on leaves and brown-brown on fruits.

Starting from the lower tiers of leaves, late blight gradually captures the entire tomato bush. In dry weather, the affected areas dry out, and in wet weather they rot.

On fruits, regardless of the degree of maturity, late blight spots have a hard structure. Growing over the entire surface, they affect not only the outer integument of the tomato, but also go deep into its tissues. They can also appear on plucked tomatoes left for ripening. Peduncles, flowers and sepals affected by phytophthora turn black and dry.

What contributes to the development of late blight?

Late blight distribution zones are quite wide and are divided according to severity into strong, medium and weak. However, even if the likelihood of the spread of this disease in your area is small, it is necessary to know what late blight is, since in addition to tomato it affects eggplants, peppers, and potatoes, and sometimes it can even be found on strawberries. Damage caused by the fungus Phytophthora infestans is often up to 70% yield loss.

Favorable period for the progression of late blight is the second half of summer, characterized by fluctuations in day and night temperatures and high humidity in the evening and morning. The disease can also be provoked by a banal excess of nitrogen introduced under the crop during fertilizing, and poor ventilation of the beds, and high density of plantings, and the presence of diseased plants among neighboring crops. Therefore, it is better not to wait for a favorable moment for the fungus, but to take care in advance to protect your tomatoes from it.

Preventive measures in the fight against late blight

1. The simplest preventive measure in the fight against late blight, recommended in most literary sources, is the choice of varieties resistant to this disease. But, completely resistant to late blight, neither varieties nor hybrids of tomatoes exist , no matter what manufacturers write on packs of seeds. To relatively stable, some agronomists include varieties: "Lyana", "Glory of Moldova", "Grot", "Gribovsky 1180", "Cinderella" and some others.

2. You can plant tomatoes that have a short growing season and are distinguished by a quick friendly return of the crop, such as "Profitable", "Radical", "Debut F1", "Sanka". Having time to form fruits in 80 - 90 days, they actually avoid the fate of being destroyed by a malignant fungus.

3. The choice of tall varieties also helps protect against late blight. Their agricultural technique includes the removal of lower leaves, which means that their plantings are more ventilated and less exposed to excessive moisture.

4. Growing crops in greenhouses gives good results, where it is easier to maintain a stable temperature and humidity. If it is not possible to organize a greenhouse, it is possible, upon the onset of cold nights, to cover the tomato plantings with a film in the evening.

5. As a preventive measure against phytophthora, before sowing in open ground or cups, tomato seeds must be treated with a 1% solution of potassium permanganate.

6. If late blight still "walked" around the garden - autumn cleaning of the beds should be especially thorough: plant residues must not only be collected, but buried in the ground or burned, garden tools must be disinfected.

7. When approaching the dangerous period, you need to monitor the cleanliness of tomato plantings from weeds, when watering, do not allow moisture to get on the leaves, carry out top dressing with a high content of potassium and spraying with boric acid (1 tsp per 10 liters of water). Subsequently, spraying is repeated two more times with an interval of two weeks, until the fruit turns red.

8. The use of growth regulators on tomatoes shows good results. "Epin plus", "Oxyhumate", strengthening the plants, give them the strength to resist the fungus.

9. The recommended preventive measure is to remove the lower leaves, as these tend to "catch" the disease.

10. At the first manifestations of late blight - affected plants must be pulled out and removed from the garden without fail.

11. If phytophthora has come to neighboring areas and the weather is favorable for its development, you can not wait until it damages your crop, but remove unripe fruits and put them to ripen, having previously disinfected them in hot water. Ripening should take place in the dark, at a temperature of approximately + 25 ° C, disinfection - for two minutes in water at a temperature of + 60 ° C.

12. Some gardeners, as a preventive measure, use an infusion of garlic (for 10 liters of water, 1.5 cups of chopped garlic, 1.5 g of potassium permanganate and about 2 tablespoons of laundry soap). The first spraying is carried out when the seedlings planted in the ground take root well (about 10-14 days after planting), the second and subsequent ones are repeated after two weeks, at the rate of 150 g of solution per plant.

However, all this is only the prevention of the disease, and based on the fact that late blight is a complex problem, it is impossible to dwell on these measures, but it is mandatory to add more significant control measures to them.

Chemical means to combat late blight

Based on the fact that the first signs of late blight on tomatoes are an indicator that the disease has already begun to progress (i. e. the fungus has been living in plant tissues for some time), to fight it, even by chemical means, it is necessary to start in advance - as soon as the thermometer began to drop to + 10 ° C, heavy dew began to appear on the plants or it rained for more than two days. It can be August or September, more often the end of July, and sometimes June.

It is necessary to choose drugs based on the fact that Phytophthora infestans develops resistance to chemicals very quickly, which means taking drugs with different active ingredients. Treatments should be carried out once a week, alternating preferred fungicides. What to apply, it is better to ask at the place of purchase. Since there is increased attention from scientists to late blight, new products are constantly appearing on the market. Of the old, proven ones, we can recommend Bravo, Ditan, Ditan M-45, Ridomil Gold.

Chemical prophylaxis should be carried out in the evening, in the absence of wind. The last spraying must take place no later than 20 days before harvest .

Microbiological agents

Microbiological preparations such as "Fitosporin" and "Trichodermin" are also quite an effective option. The microorganisms present in them actively suppress the phytophthora fungus, and the antibiotics secreted by the Trichoderma lignorum fungus also destroy pathogenic bacteria of other pathogens. However, they cannot completely destroy the brown rot of tomatoes, so they must be used in conjunction with other methods of control and prevention.

Folk remedies against late blight

Since we still grow tomatoes “for ourselves”, you can try folk remedies in the fight against late blight. Their scientific substantiation is insufficient to recommend, but still...

1. Pine shoots. Finely chop the still sticky tops of regrown pine twigs and boil them for 2-3 minutes in 300-400 ml of water. Dilute the cold strained broth with clean water 1 x 5 and spray the tomatoes.

2. Ash. Approximately 300 g of ash boil for about 30 minutes in a small amount of water. Set aside, strain, dilute in 10 liters of water with the addition of 20 g of grated soap.

3. Rotten straw. For 10 liters of water, 1 kg of rotten straw or hay, a handful of urea - leave for 3-4 days. Spraying is carried out at intervals of 1.5 weeks.

4. Copper sulfate. For 10 liters of water, 2 g of copper sulfate and 200 g of soap.

control measures, prevention. Tips from an agronomist

Tomato eater. He is hated by millions of gardeners. In a matter of days, this infection can destroy the entire crop. First, the leaves turn yellow, then the fruits become covered with brown spots and literally rot alive. Do you recognize? Late blight is a terrible word for a gardener and a sentence for a plant. Where does the insidious disease come from and is it possible to save infected tomatoes? Vasily Opimakh, an agronomist-consultant of SKARB-bio, told specifically for AGRONEWS how to deal with late blight.

Late blight, or as it is also called brown rot, is a plant damage by microscopic fungi. The main victims of the insidious disease are our favorite nightshades: tomatoes and potatoes. Phytophthora zoospores are almost everywhere: in the soil, on the surface of the greenhouse, on garden tools, on the remains of vegetation, and even on seeds. You can bring the infection to your garden, you yourself - from a neighbor in the area, through shoes.

While phytophthora is in the soil, it is considered relatively harmless to tomatoes, simply because it feeds on plant debris. The trigger for this disease can be bad weather. That is why every year, gardeners around the world hold their fists, drink a sedative and beg the heavenly office to give them a hot summer. According to the expert, in dry weather, infection of tomatoes with late blight is practically impossible.

The spores of this fungus do not tolerate sunlight. But during the period of rains and fogs, when the humidity of the air rises, they “wake up”.

As a rule, phytophthora breeds on tomatoes in the open field. However, the disease can also appear in greenhouses. Cool nights and warm days - due to these temperature fluctuations, condensation collects on the inner surface of the film. The spores need moisture to penetrate the plant more easily. Therefore, one of the main tips is to ventilate greenhouses.

In the rainy season, the chance of catching phytophthora increases, especially if the optimal temperature regime is not observed (for tomatoes it is from + 19 ° С to + 22 ° С). In addition, phytophthora loves heavily limed soil. Therefore, be careful with fertilizers. Soil and plants "overfed" with nitrogen are also a good bait for the disease.

Plants can also become infected with phytophthora from neighboring crops. Phytophthora should appear on potatoes and after 1-2 days wait for it on tomatoes, especially if they grow nearby. Therefore, the beds with these crops should be at a decent distance from each other. Another tip: do not plant tomatoes in the area where potatoes were previously grown.

A plant can be “diagnosed” by eye - the signs cannot be confused with any other disease. Starting from the lower leaves, late blight gradually occupies the entire tomato bush. A white coating appears on the lower part of the leaves, and small brown spots along the edges. Over time, the leaves wither and fall off. The same picture is on the stems. Eats late blight and fruits. The peel of the tomato becomes thin, the flesh rots, exudes an unpleasant odor.

The best treatment is prevention. You should not joke with phytophthora, here you need to be proactive. After all, when a plant gets sick, it’s sad to say, but you can put an end to them. How to prevent the disease - advice from our expert Vasily Opimakh.

First. The ideal conditions for phytophthora are lack of air. Therefore, you should not arrange "jungle" from the beds. Plant plants on them less often and remove stepsons and leaves at the bottom of the bush to the first brush.

Second. It is better to grow tomatoes in a greenhouse - this way you will be able to regulate the temperature, air humidity and soil. If you have a greenhouse, it is important to ventilate it well. You can cover the top of the beds with tomatoes with a film so that it hangs on the sides without touching the ground. So the air will circulate and the tomatoes will be sheltered from the night coolness and morning dew.

Third. Water the plants in the morning, under the roots, so that the soil dries out during the day, does not remain very wet at night.

Fourth. If you notice the blackened fruits of tomatoes - as they say, chop on the vine without sparing, otherwise, the disease will mow down your entire crop. In addition, it is better to burn the infected stems, do not send them to the compost pit. So you get the cycle of phytophthora in the garden. Be sure to sanitize garden tools.

Folk remedies as a treatment for phytophthora - placebo effect, the specialist assures. There is absolutely no guarantee that they will work 100%. Therefore, if the disease has reached the beds, do not waste time. Fighting phytophthora is not easy. But the disease can really be stopped at the initial stage. If late blight has spread to most of the plants, then heavy artillery is used here - chemicals. According to Vasily Opimakh, the most effective are those containing copper.

Bordeaux liquid, popular with summer residents, is a suspension of a solution of copper sulphate in milk of lime. A 1% solution is used: 150 g of slaked lime, 100 g of vitriol per 10 liter bucket. There are several important points. The ingredients are mixed in a strictly defined way. Lime milk and a solution of copper sulfate are prepared separately, and then they are combined in a common container. It is better to take plastic containers as dishes. You can process plants with such a mixture 4 times per season. It is impossible to store the solution, it quickly loses its properties. It needs to be used in 5-9hours.

Another recipe is copper sulphate solution. Add 2 tablespoons to a bucket of water. You need to process the entire aerial part, especially the leaves on the back, where the fungus hides from the sun's rays. Unlike Bordeaux liquid, copper sulfate is more toxic to plants. Such fungicides should not be sprayed on tomatoes three weeks before harvest. Otherwise, you can not eat tomatoes.

If there is less than three weeks left before the harvest, only biological preparations, such as Phytosporin, can be used against phytophthora. It contains hay stick. It is not dangerous to humans, and therefore it is possible to process tomatoes with such a solution until harvesting. By the way, it can also be used as a prophylaxis against phytophthora. Before sowing or planting plants, shed the soil or sometimes add the drug to irrigation water.

If late blight develops quickly, it is better to remove the fruits of tomatoes, even if they are green. But before you send them for ripening, tomatoes should be processed. Some gardeners use this method. Tomatoes are dipped into a basin of hot water (60 ° C) for 1.5-2 minutes so that they warm up. After, the fruits are dried and laid out in boxes or flat baskets. From such processing, late blight spores die and these tomatoes are quite edible.

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