White spots on cucumber leaves: how and what to treat

A healthy plant has rich green leaf blades. Uneven coloring always indicates a problem. Sometimes this isn't a serious issue, but more often, it can have serious consequences. Therefore, it's important to figure out why white spots are appearing on cucumber leaves. Based on this, it will become clear what to do to keep the plant alive and get a rich harvest.

Etiology

White spots on cucumbers can be caused by a variety of issues. They can be a temporary reaction to adverse weather conditions, poor agricultural practices, or a symptom of a serious disease or pest attack. To identify the source of the problem, agronomists recommend paying attention to the overall condition of the plant and any accompanying symptoms.

Burn

Although cucumbers are sun-loving plants, they don't respond well to direct sunlight. Sunburn typically occurs when water splashes on the leaves in clear, hot weather. The droplets, like lenses, then burn healthy tissue. Therefore, watering should be done either in the morning or evening. Sunlight is detrimental to newly planted cucumber seedlings, as the tender leaves of young plants take a long time to adapt to the environment.

Distinguishing sunburn from other conditions is easy. Simply analyze your plants' watering history and compare this with recent solar activity. It's important to ensure that there are no other signs of damage other than white spots. There is no cure for sunburn. In this case, you should reconsider your watering schedule and protect the beds from the sun by using a light-diffusing cover.

Powdery mildew

The formation of a white coating on cucumbers in a greenhouse or in the open field is one of the main signs of powdery mildew. Small spots, visually resembling flour, become visible on the leaves. Over time, these spots spread to the entire leaf blade, causing it to dry out and turn yellow. Powdery mildew can only appear after infection by obligate parasites. These parasites actively reproduce at high humidity and temperatures around 20°C. Agronomists claim that under these conditions, three days are enough for the leaf to become completely infected.

Powdery mildew doesn't appear on vigorous plants. It more often attacks weakened seedlings. Plants exposed to extreme temperature fluctuations are at risk, as their phytoimmunity is weakened. Insufficient light can exacerbate the problem. Seedlings grown on balconies without the use of artificial lighting are often affected.

White mosaic

White mosaic is a viral disease. The disease primarily develops in living plant cells, but the pathogen can also be transmitted through dead leaves. The virus can remain in the soil or on tools for extended periods. Once it reaches a healthy leaf, it begins to break down chlorophyll. As a result, the plant's carbohydrate levels decrease.

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White mosaic typically affects greenhouse plants. The following factors are triggering the disease:

• dense plantings;
• air temperature changes;
• high indoor air temperature.

The main symptom of white mosaic disease is the appearance of light-colored spots, initially with fuzzy borders. They are located near the veins. Gradually, the affected areas expand, and eventually the entire leaf turns white or yellow. This condition inhibits plant growth and reduces yield. White mosaic disease often also appears on seedlings that have recently been transplanted to their permanent location. Young leaves and shoots are affected.

Downy mildew

Downy mildew (peronosporosis) causes yellow, oily spots to appear along the veins on the upper surface of the leaf blades. A white, purple-tinged coating forms on the underside of the cucumber leaves. The spots soon spread, and the affected areas turn brown. The coating thickens. The leaves begin to dry out and become brittle. Tissue may fall out in some areas of the leaf. This can lead to complete baldness of the plant.

https://youtu.be/FMRAmAv0nH8

Spider mite

The parasite can inhabit various garden, ornamental, and vegetable crops, but most often it attacks cucumbers. Favorable conditions for the pest – warmth, dry air, and poor ventilation. Spider mites can be found on both seedlings and mature plants. The main sign of their presence is the presence of small white spots on the leaves. These are bite marks from where the pest sucks sap.

The largest concentration of bites is found near the petiole, as the pest moves along the plant stem and, upon reaching the leaf blade, immediately satiates its hunger. Web-like threads can also be found. As the problem progresses, they become a continuous web covering both the leaves and stems. If you look closely, you can even see the pest itself—an arachnid a few millimeters long—on the cucumber leaves. It's easy to recognize if you look at the photo first.

Ascochytosis

Ascochyta blight most often affects weakened plants. It is caused by a pathogenic fungus that is transmitted through the soil or carried with organic debris.

Its main symptoms include white or brown areas along the edges of leaf blades. Over time, white spots appear across the entire cucumber leaf. The affected area dries up.

Diseased plants' growth is stunted, and a coppery exudate appears on the stems. The vegetables also mutate. Eventually, they appear as if they've been boiled, and their surface becomes covered with black spots. They should not be used for cooking. Ascochyta blight is most severe during the fruiting period. Risk factors include general plant weakness, high humidity, and poor crop rotation.

Anthracnose

Anthracnose (copperhead) is also a fungal disease. It affects all plants in the cucurbitaceae family. It is one of the most common causes of leaf spots on cucumbers in greenhouses. Infection sources include plant debris, insects, seeds, irrigation water and precipitation, wind, and urban debris. The pathogen thrives at temperatures between 4 and 30°C and humidity around 90%. When humidity drops to 60%, the fungus enters a state of suspended animation and remains inactive. Anthracnose also occurs in open ground, although it is rare.

Infection can occur at any stage of plant development, so both seedlings and mature bushes need to be inspected. The abnormal process begins at the base of the bush. Brown dents begin to appear on the root collar and stems. Initially small, they eventually enlarge, causing the stem to break.

Next, yellow or brown spots ranging from 5 mm to 40 mm in diameter appear along the leaf edges and veins. These spots gradually spread to the stems. The white spots on the cucumbers also merge and fall out, eventually forming holes. The affected stems become brittle. Elongated pink spots may appear on the cucumbers themselves, extending up to half a centimeter into the vegetable. The affected plant dies.

Use of folk remedies

Folk remedies are often sufficient in the early stages. Their advantage is their safety. They have no harmful effects on vegetables, so the harvested crop can be eaten after watering. There are many folk remedies, all equally effective. Before treatment, affected leaves should be removed and burned.

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For different diseases, different remedies need to be used:

1. Powdery mildew. Pour 40 g of washing soda into a bucket of warm water and stir.
2. Downy mildew. Pour 400 g of onion peels into 10 liters of water, bring to a boil, and let the mixture sit in a warm place for 3 days.
3. Spider mites. Brew 60 g of mustard powder in 1 liter of water and let it steep for 3 days in a sealed container. Then add another 3 liters of water to the resulting mixture.
4. Anthracnose. Dissolve 1 kg of ash in 10 liters of water. To improve the treatment's adhesion to the foliage, you can add shavings of tar soap.

Use of chemicals

In severe cases, the use of commercially available products is warranted. Antifungal products (such as Bayleton or Vitaros) are effective against powdery mildew and downy mildew. Spider mites are controlled with acaricides or insectoacaricides (such as Actellic or Neoron). Anthracnose can be treated with contact or systemic antifungals. Agronomists recommend using Poliram or Quadris.

Ascochyta blight is difficult to control. Products such as Saprol or Thiram are quite effective. These products should be purchased from specialized stores, and it's important to pay attention to their expiration dates. For the treatment to be most effective, it's important to treat not only the affected plants but also nearby healthy ones, as well as the soil in which they grow. If most of the plant is covered in spots, it won't be possible to save it.

Prevention

White spots on cucumbers can be prevented by following these guidelines:

• regularly remove weeds and loosen the soil;
• When planting crops, maintain a large distance so that air can circulate normally between the bushes;
• water plants only with warm water, preferably at the roots;
• After completing the work, disinfect the equipment;
• stick to crop rotation, do not plant seedlings in the same place every year;
• perform mulching;
• apply fertilizers in a timely manner.

White spots on cucumber leaves are normal. If they have already occurred, gardeners should analyze the events that preceded them. Once the root cause of the problem is identified, appropriate treatment can be selected. Timely action can help preserve the plant's life. And to prevent the problem from recurring, proper care is essential.