Methods of control, treatment and prevention of white and gray rot on cucumbers

Cucumbers are susceptible to five types of rot, all caused by pathogenic fungi. Plants grown outdoors with adequate ventilation are less susceptible. Greenhouse plants remain at constant risk, even if they are immune to the fungi. The development of spores is influenced by excessive moisture, dense plantings, contaminated soil and other factors.

Why do cucumbers rot?

Growing cucumbers indoors is challenging. It requires constantly maintaining a specific microclimate, monitoring the soil composition and condition, limiting vine growth, and performing preventative treatments. Only by following a comprehensive set of agricultural practices can you expect a bountiful harvest. In open gardens, things are a bit simpler.

In open ground, cucumbers can avoid rotting even in adverse weather, but only by rotating the crop's location and choosing the right predecessors (onions, cruciferous vegetables, legumes, and nightshades). Greenhouse conditions greatly complicate crop rotation. Annual, complete replacement of the topsoil, which harbors fungal spores and harmful insect larvae, is required. The main causes of rot are:

• violation of temperature regime;
• improper watering;
• unregulated air humidity;
• over- or under-nutrition;
• lack of ventilation;
• cold drafts;
• cramped conditions;
• ignoring disinfection.

The infection can be brought into a greenhouse or outdoor garden beds on shoes and garden tools. The soil in which the seedlings grew, as well as seeds, can also be a source of contamination. Aphids and whiteflies carry the spores. Problems arise with neglected plants or improper harvesting. Old vines, overgrown cucumbers, and yellowed leaves should be removed. Cucumbers should be grown only on trellises or twine, preventing the ovaries from coming into contact with the soil. Cucumbers should be cut or picked carefully, avoiding mechanical damage and always including a portion of the stem.

Types of rot

Cucumbers (both in greenhouses and outdoors) are most often affected by two types of rot: white rot and gray rot. These diseases share a common nature—the fungi develop and multiply under similar conditions—but they manifest differently on plants. Both rots can be treated with similar methods (chemical, biological, and folk remedies). The sooner symptoms are identified, the easier it is to save the plants.

White rot or sclerotinia

Outbreaks of the disease occur during periods of unfavorable weather (frequent rainfall, cool temperatures, and sudden changes in day and night temperatures). Sclerotinia is especially active in high humidity and constant temperatures of 10–16°C. Rot spots are concentrated at the branching points of the shoots and at the base of the stem. At first, they appear wet in appearance, then become covered with a white, cottony coating. The bushes' ability to receive water and nutrients from the soil is disrupted.

The lesions gradually increase in size, the mycelium and sclerotinia grow, then dry out and fall off. Dark, rounded sclerotia form within the mycelium. The plant tissue in these areas softens and becomes slimy, and the stems break. The flesh of the affected fruits becomes flabby, watery, and bitter, the skin becomes covered with a white, fluffy coating, and the green fruits quickly rot. The plant gradually wilts and dies.

Gray rot

Once on the plant, the fungus begins spreading enzymes and toxins, damaging the tissues and feeding on their sap, spreading through vines, leaves, and cucumbers. At the end of the season, the spores fall into the soil and germinate again in the spring. Gray mold is especially dangerous at temperatures of 16–17°C and constant humidity of around 90%. The first signs become noticeable only a week after the initial infection. Initially, the infection appears on cucumber stems, near branches, and in the axils of the leaves.

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Small, irregularly shaped, yellow-brown spots appear on the leaves. Gradually, the lesions become moist, and a border of dead tissue appears. The affected areas become brittle, and the flower stalks and buds take on a grayish-brown hue. The stem may rot from the base or in separate sections along its length, with the damaged areas becoming covered with diffuse spots. A fluffy, gray coating appears on the tips of the fruit, eventually covering the entire fruit. The bushes stop developing and dry out.

How to cure cucumbers from gray and white rot

Diseases are easily treated only when the first signs of fungal growth appear. First, trim off all affected parts of the plant, and sprinkle the cut areas with crushed chalk or activated charcoal, lime, sifted wood ash, or tobacco dust. If the lesions are concentrated at the base of the stem, carefully scrape away the rotten areas down to healthy tissue, then treat these areas with special mixtures:

• Mix powdered chalk with equal parts of Rovral or Semileks, adding a little warm water to form a thick paste. This mixture is more suitable for treating white rot on cucumbers in greenhouses and open fields;
• 200 g of wood ash is mixed with 5 g of copper sulfate, a small amount of wallpaper glue (CMC) and water.

After pruning and removing damaged bushes from the garden beds or greenhouse, remove all plant debris, including mulch, and burn it outside the garden. Experienced gardeners recommend immediately replacing the top layer of soil (up to a depth of 3 cm), very carefully to avoid damaging the cucumber roots. Sprinkle the surface of the beds with wood ash (a half-liter jar per square meter). Next, assess the extent of damage to the bushes and choose appropriate control methods.

Folk recipes

Combating fungi with homemade remedies, herbal infusions, or decoctions is only advisable for mild cucumber infestations, and can also be used as a preventative measure. If the infestation has spread to most of the vines, the leaves, and especially the cucumbers, folk remedies will be ineffective. The most effective recipes for spraying cucumbers:

• a liter of milk, 5 g of iodine and grated laundry soap per 5 liters of water;
• 75 g of baking soda per bucket of water;
• 30 g of tar soap is dissolved in 10 liters of water and left for about 12 hours;
• 3 liters of whey, 1 teaspoon of copper sulfate per 10 liters of water;
• Fill ¼ of a bucket with fresh, finely chopped horsetail, add 3 liters of water, bring to a boil, reduce heat, and simmer for half an hour. Cool the infusion, strain, and add water to make a 10-liter solution.
• 150 g of garlic cloves are finely chopped, infused in 10 liters of water for 24 hours, and filtered;
• 100 g of pressed yeast is dissolved in 10 liters of warm water;
• 2 g of copper sulfate, 10 g of urea are diluted in a bucket of water, 40 g of liquid or laundry soap are added;
• 300 g of wood ash is boiled for 15 minutes in 5 liters of water, then brought to a volume of 10 liters, infused for 5 hours, filtered;
• 80 g of copper sulfate and 50 g of soda per bucket of water.

Some over-the-counter remedies are quite effective in combating white and gray mold. For 10 liters of water, mix 10 ml of brilliant green, 1.5 g of potassium permanganate, 10 g of boric acid, and 30 drops of iodine. Each solution is used separately, adding a small amount of liquid or laundry soap to the solution. Dusting cucumber bushes with a mixture of ash and copper sulfate at a ratio of 1:0.5 also helps. Because of the short duration of action, plants are treated with these folk remedies 3-4 times in a row, spaced 4-6 days apart.

Biological protection agents

When chemicals are unavailable or undesirable, use products that are safe for humans, animals, and beneficial insects. Cucumbers can be sprayed with biological products safely even during the peak fruiting period, when cucumbers are harvested daily. The active ingredients are sensitive to sunlight, so plants should be sprayed in the evening, early morning, or during cloudy but dry weather. Which products help combat gray mold and white mold?

• Gamair;
• Fitosporin;
• Gliocladin;
• Planriz;
• Pentafag-S;
• Barrier;
• Trichodermin.

All products should be used according to the instructions, observing the dosages; they may vary. Biological products do not take effect immediately; results may become noticeable within 12–48 hours. Affected cucumbers should be sprayed at least four times, every five to seven days. Safer products are used as a preventative measure, spraying cucumbers every two weeks or during periods of poor weather.

Chemicals

Chemicals help quickly combat fungus, even if it has already affected a large portion of the crop. These treatments are applied very carefully, observing the timeframe between treatment and harvest. Cucumber treatment solutions vary in their formulations, with concentrations depending on the severity of the infestation, the stage of plant growth, and the area being treated. Copper-based solutions are used against fungal infections.

Treatments with any preparations or folk remedies are only permitted in the morning or evening, in dry, windless weather. Spray the bushes with a fine mist sprayer, first from the bottom up, then back down, ensuring to cover the stems, leaves on both sides, and the area around the trunk. When working with any mixtures, be sure to wear personal protective equipment.

If diseases appear on cucumbers in a greenhouse, after spraying the plants, ventilate the room and thoroughly treat the greenhouse soil, glass, and other structural elements with HOM. Three to four days after the initial spraying, apply a foliar feeding to the cucumbers with a mixture of 10 g of urea, 2 g of copper sulfate, and 1 g of zinc sulfate per bucket of water. This mixture helps normalize metabolism, strengthens plant tissue, and prevents the spread of diseases.

Prevention of gray and white rot

Dangerous infections in cucumbers can be prevented by carefully following proper agricultural practices. Seeds collected at home must be disinfected, as must store-bought seeds unless the packaging indicates pre-treatment. The seeds are soaked in a 1.5% potassium permanganate solution for 20 minutes. The soil mixture for seedlings is baked in the oven for about an hour at 80–90°C.

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Basic rules for growing and caring for cucumbers:

1. All melons and gourds are not grown in heavy soil types; they thrive only in loose, permeable, non-acidic, and structured soil, such as sandy loam or clay loam. From spring to fall, care is taken to prevent a dense crust from forming on the soil surface, which would impede air penetration to the roots. After each watering or rain, the soil is loosened shallowly.
2. Excessive moisture is the main cause of cucumber infections. Plants should be watered regularly but moderately at all stages of development; avoid allowing the soil to dry out or become waterlogged. Reduce the frequency of watering in cool weather. Use only settled, warm water (at least 22°C).
3. Humidity in the greenhouse is monitored; it should be between 85–95%. At the maximum permissible level, care is taken to prevent condensation from accumulating on the leaves and walls of the greenhouse. To achieve this, the room is frequently ventilated, and the windows and doors are closed completely only on cold nights.
4. Weakened plants are more susceptible to rot, so cucumbers should be grown only in fertile soil and fertilized regularly (every 7-15 days). Nitrogen fertilizers should only be used before flowering, followed by complex mixtures containing phosphorus and potassium. Overfeeding cucumbers is also a must, as too much of any nutrient will impair their development.
5. Cucumbers are heat-loving, but they also don't tolerate extreme heat. When grown in a greenhouse, ensure the temperature doesn't drop to 18–16°C or rise above 28–30°C. The optimal temperatures for growth and fruiting are 24–28°C during the day and 18–22°C at night.
6. The crop cannot be planted in the shade; the bushes develop poorly and are constantly susceptible to disease. In poor light, the soil barely dries out, maintaining a constant, high humidity.
7. Dense plantings and overgrown weeds create optimal conditions for fungal growth. Cucumbers are planted according to a free pattern or the recommendations on the packaging (for a specific variety or hybrid). Weeds are removed as they grow, root and all.
8. During the season, several preventative sprayings are carried out against diseases and pests using biological preparations or folk remedies.

In the fall, remove tops, weeds, and mulch from the beds and dig them up to a spade depth. If cucumbers have been affected by white or gray mold this season, water the soil with a solution of 50 g of copper sulfate per 10 liters of water (2 liters per square meter). Some spores can be killed by treating the soil with hot steam or boiling water. In the greenhouse, the top layer of soil is also changed (to a depth of 15 cm). All parts of the greenhouse structure are treated with a 10% mixture of copper or iron sulfate. In the spring, the beds are treated with a Trichodermin solution, especially if replanting is planned.

Providing comfortable conditions for plants is a gardener's primary responsibility. Following simple recommendations will eliminate the need to wonder why cucumbers are rotting in the greenhouse or open-air garden, or what to do about it. Early detection of rot and prompt treatment will ensure the preservation of the majority of the harvest. If diseases do appear and spread too quickly, don't neglect chemical treatments; it's better to sacrifice a few cucumbers than to lose the entire plant.