Spots on cucumber leaves: causes and treatment

Yellow spots on cucumber leaves indicate that the plant needs help. Ignoring this signal is a bad idea, as you'll lose your harvest. But don't immediately resort to chemicals; first, figure out why the leaves are covered in rusty spots. Sometimes it is enough to change the watering regime or simply weed the garden bed.

Causes of yellow spots on leaves

Every gardener's goal is to preserve their harvest. Spots on cucumber leaves in a greenhouse or in the open ground can be a symptom of growth and vegetation problems. Even if the fruits are partially saved, they will be less juicy, twisted, and slightly bitter. And the seedlings planted in the same spot will die the following year. What to do if yellow spots on cucumber leavesThe exact amount depends on the type of defect, the size, and the growing conditions. It's important to inspect the entire vine, check the watering quality, and analyze when surrounding plants shade the cucumbers and how long they need to spend in the shade.

Fungal diseases most often affect the root zone. This area requires special attention. Next, turn the leaf blades over and examine the veins—this is the most vulnerable area.

Illumination

Leaves turn yellow when there's insufficient light or when the plant is exposed to direct sunlight all day. In the former case, the lower leaves of the plant are most affected, while those higher up turn pale. If there's too much light, the yellow spots resemble burns. The affected area dries out and becomes thinner.

Humidity and temperature changes

With regular watering, plants planted in a greenhouse don't suffer from dehydration. Film-covered frames reduce evaporation. Open soil, especially in hot weather, dries out quickly. Humidity is determined not only by the frequency and amount of watering, but also by air temperature, season, local climate, and natural precipitation.

Yellowing of the leaf blade due to insufficient watering begins at the edge, appearing as a dry edge. The discoloration then spreads to the entire surface and the shoots. The tips of the shoots are the first to suffer. The optimal humidity for cucumbers is 75%. If it's lower, growth stops and cucumbers will be lost.

The plant changes color with sudden temperature changes. If the daytime temperature is 22-30°C and the nighttime temperature is 16-18°C, the range is acceptable. It's best when the daytime temperature isn't too hot, and the nighttime temperature drops no more than 4-8°C. Otherwise, the plant either dries out or stops growing. In cold summers, seedlings are planted only in greenhouses or covered with plastic.

With frequent, small waterings, the moisture doesn't have time to be absorbed and saturate the root system; most of it evaporates. With infrequent, heavy watering, the foliage turns brown, and the fruits become bitter. With too much water, the root collar is exposed, and splashes on the leaves cause yellowish patterns and burn-like spots on cucumbers.

Plant infection

Each one a disease affecting cucumber vines, has characteristic symptoms. Photos will help determine the cause of the defect:

1. Cucumber mosaic is a viral disease. Leaf blades become covered with small spots that gradually enlarge and develop into streaks. There are several types of mosaic: tobacco, green, white, speckled, and common. The disease is caused by viruses that invade the plant tissue, destroying chloroplasts.
2. Downy mildew, or peronosporosis, begins after a fungal infection. Cucumber leaves turn yellow on top, covered with irregularly shaped (square or rectangular) reddish spots, and a bluish, whitish, or lilac-colored coating appears on the underside. The bark cracks, shoots lose vigor, buds fall off, and fruit formation ceases.
3. Copperhead, or anthracnose, is caused by the spread of colletotrichum spores. The parasitic fungus develops on all parts of the plant. Dark spots form near the roots, and the shoots become soft and easily broken. Initially, yellow spots may appear on the lower leaves of the cucumber, and then the entire plant becomes affected. The affected areas are quite large, up to 4 cm in diameter, and they peel and crumble, causing the leaf blade to develop a patterned appearance. Optimal conditions for the fungal growth are temperatures above 25°C and high humidity.
4. Cladosporiosis is also a fungal disease. This pathogen thrives in cool conditions and develops quickly in stagnant air, so it prefers greenhouses. The disease can be identified by the appearance of yellow spots that gradually enlarge and merge into spots.
5. Alternia leaf spot. If the plant is infected with spores, slightly raised, dry spots appear on the underside. It most often attacks seedlings in greenhouses, preferring those located near the entrance.

Pests

The appearance of yellow spots on cucumber leaves is caused by pestsThe following signs indicate infection:

1. Spider miteThe sticky surface of the underside of the leaf blade is due to the webbing and small light specks on the top.
2. Aphids. These small, translucent insects are difficult to spot, but a sticky film on the surface of plant parts indicates an infestation. This is honeydew, a liquid secreted by the insects. Ants love it.

1. Whitefly. A translucent insect resembling a moth or white fly. Like aphids, it feeds on plant sap.
2. The shoot fly is harmless in itself, but it lays eggs in leaf axils and bark crevices. The hatched larvae destroy young leaves.
3. Slugs. They gnaw at the shoots, causing premature leaf fall and wilting.

Cucumber midges and root-knot nematodes cause no less damage.

Incorrect application of fertilizers

Cucumbers absolutely need fertilizing. Excess leads to rot, while a deficiency can impair growth and vegetation. A manganese and iron deficiency causes dark veins, while wilting and yellowing of the upper leaves indicates a magnesium deficiency, while a potassium and magnesium deficiency is indicated by pale, curled leaf edges.

The safest cause of yellow spots on cucumber leaves is the plant's aging. This is a natural process and doesn't require any treatment. However, there are methods for rejuvenating the plant.

Treatment methods

Gardeners decide for themselves which methods to use: spraying with chemicals or using folk remedies. But first, they need to ensure adequate lighting, remove damaged parts, tie up the vines so they receive even sunlight, and trim off any interfering branches. If yellowing appears on young seedlings, they should be thinned out or replanted.

Watering should be consistent. It's recommended to water once every 2-3 days, depending on weather conditions. The recommended watering rate is 1 bucket per 12 m3. If you can't visit the garden more frequently, cover the bed with agrofibre to reduce evaporation or apply mulch.

During heavy rainfall, a mulch of sand or wood chips will also help, as they absorb water. The top layer of soil should be loosened to increase evaporation. Water either in the morning or after 5-6 PM, directing the stream at the roots. As mentioned earlier, splashes on the vines can cause spots on cucumbers and leaves.

Plant disease control

To cure a plant infected with fungal diseases, it must be treated from the roots to the upper shoots:

1. Topaz, Fundazol, Fitosporim, and bacterial biofungicides are used to combat powdery mildew. The safest biological products are Rizoplan, Gamair, Alirin-B, and similar ones. If children and pets are constantly present in the area, it's better to use folk remedies. For example, spraying with a soap-ash solution: half a cup of ash and 100 grams of laundry soap per bucket of water, let it steep for two days. Another option is treating the area with whey or sour kefir.
2. Treating anthracosis with home remedies is ineffective; chemical treatments are required. These include Ridomil, Quadris, Skor, Acrobat, and Oxicom.
3. To suppress the spread of Cladosporiosis, plants should be treated with copper-containing products. These include Bordeaux mixture and Hom. Folk remedies are effective only at the first signs of the disease. Mix 2 liters of milk, 60 drops of iodine, and 40 g of grated soap, let it steep for 6 hours, and spray the plant every 10 days until fruit set. Another method is to pour 50 g of crushed garlic into 1 liter of warm water and let it steep for 24 hours.
4. To treat Alternia wilt on cucumbers planted outdoors, the same treatments are used as for Cladosporiosis. At the first signs of the disease in greenhouses, use "Poliram."

Even if the plant is saved, after the gardening season is over, all shoots should be burned, the bed cleared, and re-treated with chemicals. Cucumbers should be replanted no sooner than four years later. When using fungicides, strictly follow the instructions.

Insect control

Gardeners prefer to combat pests with folk remedies. The most effective methods are:

1. To combat spider mites, spray with a solution of laundry soap or ammonia.
2. Aphids dislike strong odors. Plants are treated with an infusion of tobacco or citrus peel. To make a "medicine" from tobacco, remove it from a pack of Prima, add 5 liters of water, and let it steep for 24 hours. A saturated solution of dried lemon or orange peels is made as follows: pour 1 liter of boiling water over the peels (from a 0.5-liter jar), let it steep for 24 hours, and then boil for 10 minutes. Before spraying, dilute the solution in 10 liters of water.
3. Traps can help control whiteflies. You can hang up fly tape or pieces of cardboard coated with a mixture of honey and vegetable oil.
4. Sprout fly. These pests cannot be controlled without insecticides. Fufanon and Detox are used for spraying, and Iskra and Attelik are used for seed treatment. Cyperus has a broad spectrum of activity.
5. Slugs are collected by hand, and the beds are treated with liquids with a strong odor or bio-infusions produced in industrial conditions.

To prevent leaves from turning yellow, fertilize the area where you plan to plant cucumber seedlings in the fall. Use organic matter, humus, wood ash, or silage, and water with urea. If you encounter the problem after planting, you can try this method: dissolve 25 g of ammonium nitrate in a bucket of water and water the bed 2-3 times, 7-10 days apart. To enhance the effect, treat the soil with a solution of nitroammophoska. The dilution ratio is 1 tbsp. per 8-10 liters of water.

Prevention of yellowing of leaves

To prevent cucumber vine leaves from turning yellow in hot weather, ensure the soil stays moist and the root system gets adequate air circulation. To achieve this, water the beds regularly, drain excess water after heavy rains, and loosen the soil crust. Disinfect the planting material and treat the beds with fungicides. Remove weeds and dried leaves promptly. Thin out any dense growth if the seedlings are growing too close together.

Spraying is done not only when problems arise but also as a preventative measure. As soon as the seedlings have taken root and the first leaves (3-4) have appeared, treat them with a solution of grated laundry soap, iodine, and milk. The proportions are: 20 g/3 drops/1 l. Dilute the solution in a bucket of water and spray the plant three times every 10 days. When flowering begins, treat the shoots with an alkaline solution—1 tablespoon of baking soda per bucket of water. These measures will help prevent fungal infections.

To prevent nutrient deficiencies, apply fertilizer (read the instructions before applying). If cucumbers are planted in a greenhouse, maintain a constant temperature and humidity, and control lighting. Responding promptly to leaf color changes will help preserve the harvest.