Cucumber bacteriosis: treatment and prevention measures

Cucumber is a heat-loving crop and in a changeable climate it is susceptible to infections that affect different parts of the plant. One of the most common diseases of cucumbers is bacterial blight., It occurs in both open ground and greenhouses due to excess moisture and low temperatures. While unfavorable conditions can be avoided in a greenhouse, this isn't always the case in open ground. Therefore, it's important to know how to prevent the spread of infection, how to treat it, and what preventative measures can be taken.

Causes and symptoms of the disease

The infection is caused by the pathogenic microorganism P. Syringae pv. Lachrymans, which causes tissue necrosis. This non-spore-forming gram-negative bacterium is tiny—0.8 x 1.0-2.0 µm. It parasitizes cucumbers, melons, and, less commonly, pumpkins, watermelons, and squash. The pathogen develops within plant tissues, remaining active for a long time on plant debris. In the soil, at depths up to 25 cm, the dried exudate remains viable for about three years.

How does it manifest itself?

All parts of the plant are susceptible to infection, most often during the germination and flowering stages. The disease begins with the appearance of small, oily, dark green spots in the center and along the edges of the cotyledons. These spots later develop into ulcers and gradually spread to the entire leaf, with the diseased tissue turning brown. Severely infected seedlings may die.

On mature plants, infection begins on the lower leaves, where angular, oily spots appear on the undersides, demarcated by veins. Because of the shape of these spots, the cucumber leaf disease is also known as angular leaf spot.

In inclement, damp weather or early in the morning, yellowish, cloudy droplets—bacterial exudate—are clearly visible near the spots. These droplets are easily washed away by rain and water during irrigation, which can lead to their contact with healthy tissue. When the relative humidity drops, the droplets dry, forming a film. The tissue at this point turns gray, dries, and falls out, leaving a hole in the leaf. If the infestation is severe, only the veins remain.

Infected fruits, stems, and petioles become covered with small water-soaked spots, which then dry out, penetrate deeper into the tissue, and develop into ulcers. As a result, leaves fall off, the bush stops growing and developing, the fruits become deformed, and the flesh becomes corked. Through the ulcer, the pathogen penetrates the flesh, reaching the seed coat and its inner layer. When infected seeds are planted, bacterial blight immediately appears on the seedlings.

A secondary manifestation of the infection is bacterial fruit rot, which most often occurs in greenhouse conditions. The fruit becomes soft and rots. It cannot be disposed of on the property.

Sources of infection

The disease spreads rapidly in warm, damp weather with frequent watering. There are several sources of infection:

• infected seed material - the pathogen can be on the shell, inside the seed, and is active for 1.5-1.8 years;
• rotting plant remains on the soil;
• particles of dried diseased tissue are carried by wind, insects, and raindrops;
• unprocessed tool.

Consequences of the disease

Due to the characteristics of the pathogen, the damage from the disease can be quite significant. Possible consequences:

• even with minor damage, yields are reduced by 30-50%;
• all parts of the bush become infected, which eventually dies;
• contamination of the soil and neighboring plants occurs;
• the fruits either do not develop or rot, and those infected at the development stage become deformed, do not ripen, lose their marketable appearance, cannot be stored, and lose their taste;
• secondary infection is possible, for example, brown spot, root rot;
• If 70-80% of the bush is affected, then it is useless to start treatment.

Protective measures

To protect future plantings, various methods are used using chemical, biological and folk remedies.

Seed treatment

Seeds are disinfected using high temperatures, chemicals, and biological agents. High-temperature treatment is difficult to perform at home, but it's quite possible if you have a drying oven or thermostat. To do this, seeds are heated at 50-52°C for 72 hours, then at 78-80°C for another 24 hours.

You can treat with the fungicide Apron XL (2.5 ml/kg), 0.02% solution of zinc sulfate (soak for 24 hours at room temperature).

Use of biopreparations:

• soak in Agat 25-K (9 g/kg), Pseudobacterin-2 (0.1 l/kg), Phytocide (2.5 ml/kg);
• use products based on hay bacillus (Alirin-B, Gamair, Baktofit, Fitosporin-M, PhytoDoctor) - the bacterium Bacillus subtilis suppresses bacterial and fungal infections in the early stages.

Biological preparations not only increase resistance to various pathogens, but also activate growth, reduce germination times, and increase yields by 25-30%.

Processing bushes

The same biological products based on hay bacillus are used for spraying bushes as for seeds, but the treatment is repeated 4-5 times per season, as the bacteria quickly lose their potency in the air. If desired, a similar product can be prepared at home.

Cooking steps:

• hay or hay dust that has begun to rot is placed in the shade and sprinkled with water three times a week;
• after 21 days, the dust without signs of mold is crushed;
• mix chalk powder (1 teaspoon), chopped hay (100 g), 1000 ml of water, bring to a boil and boil for a third of an hour (during this time all pathogens die, but the hay bacillus does not, because it is resistant to such temperatures);
• the decoction is infused for at least 4 days to increase the number of bacteria;
• when a film appears on the surface, the decoction (mother culture) is ready;
• infusion for spraying - hay (1 kg) + lime (5 tbsp) + mother culture + water (5 l), cover with a lid and leave in a warm place for 3-4 days.

Fighting with folk remedies

Seedlings, young shoots, and fruiting bushes are recommended to be treated with proven folk remedies that are easy to prepare and can be used without harm to human health:

• onion peel infusion – place the husk in a jar (1 l) + warm water, leave in a warm place for two days, drain, squeeze out the husk, dilute with water 1:5, every 10 days, until the symptoms of the disease disappear, spray the entire above-ground part in the evening before sunset;
• brilliant green and boric alcohol (1 teaspoon each) + a bucket of water, stir, spray once every three weeks until the bacteriosis disappears.

Preventive measures

Treating a diseased plant is difficult and not always effective; it is much easier to carry out a series of simple preventative measures.

What you can do in advance:

• plant cucumbers in a sunny area protected from the wind without retaining moisture;
• do not thicken the plantings, tie up the vines - in a vertical position, air circulates better, moisture is not retained, and there is less contact with neighboring bushes;
• ensure oxygen access to the roots by regularly carrying out surface loosening;
• water at the roots, between rows with settled, warmed water (water should not get on the leaves, stems, flowers);
• grow cucumbers in a ventilated greenhouse, where you can maintain the necessary temperature and humidity, and limit access for insects that carry the pathogen;
• use hybrids and varieties that are resistant to infection, for example, Masha F1, Murashka F1, Lesha F1, Octopus F1, Amur F1, Connie F1, Angelina F1, Competitor, Delicatessen, Far Eastern 6, 12, Nezhensky 12;
• Use healthy fruits to prepare seed material;
• the remains of diseased plants should be burned or removed from the site;
• disinfect the tools, frame, and walls in the greenhouse;
• inspect plantings and promptly remove infected leaves, flowers, fruits, and stems;
• treat seeds with Fitolavin-300, TMTD;
• In the fall, dig up the area - deep digging kills bacteria in the winter; in a greenhouse, change the top layer of soil;
• at intervals of two weeks, feed with humus, compost infusion solution, and green infusion;
• carry out preventive treatments with Hom (40 g/10 l), Energen (5 ml/10 l);
• observe crop rotation.

Prevention is better than cure, so timely prevention can help prevent bacterial infection of cucumbers and ensure a good harvest of vitamin-rich fruits.