June 18, 2025, 9:23 am | Read time: 4 minutes
Powdery mildew is a fungal disease that can affect cucumbers as well. It’s important to distinguish between powdery mildew and downy mildew. MyHOMEBOOK explains what hobby gardeners should know about this disease in this article.
True and downy mildew can be easily distinguished from each other. They not only show different damage patterns and appear on different parts of the plant, but also occur under different weather conditions. However, both true and downy mildew can affect cucumbers. Gardeners can learn here how to protect cucumber plants from infection and what to do if one of the fungi does appear.
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Distinguishing True and Downy Mildew on Cucumbers
There are many different mildew fungi. However, a general distinction is made between true and downy mildew. Cucumber mildew is one of the most common diseases of the plant. The fungi can be easily distinguished based on the damage pattern.
True Mildew
True mildew is often referred to as a “fair-weather fungus.” The reason: The responsible fungi, including “Sphaerotheca fuliginea” and “Erysiphe cichoracearum,” appear especially in sunny and dry weather. Therefore, cucumber plants grown in greenhouses are often affected. Ideal conditions for the fungal spores prevail there, which are spread by the wind with changing humidity.
An infection with true mildew on cucumbers is easily recognized by the white, powdery fungal network on the upper side of the leaf. The fruits usually show no signs of disease.
Downy Mildew
Unlike true mildew, downy mildew thrives in moist conditions. Downy mildew is caused by oomycetes and occurs in both greenhouse and outdoor cucumbers. An infection is recognized by yellow, angular spots on the leaf surface. Additionally, a gray, fluffy fungal lawn is found on the underside of the leaf. Downy mildew can sometimes affect not only the foliage but also the stems and flowers.
The damage caused by downy mildew can be considerable. The spores not only spread quickly but can also lead to the entire plant dying.
Also interesting: 4 Common Mistakes When Fertilizing Cucumbers
What Can Be Done About Mildew on Cucumbers?
Mildew is one of the most widespread plant diseases. If signs of true or downy mildew are discovered on your cucumbers in the garden, quick action is required. The spores can spread rapidly and infect other plants in the bed.
If only a few leaves are affected by true mildew, the affected leaves can be cut off and disposed of in the household waste. Mildew-infected plant parts should never end up in the compost, as the spores can continue to spread there. In case of a more severe infestation, hobby gardeners should resort to fungicides–this applies to both true and downy mildew on cucumbers. To further strengthen the plants, they can be sprayed with horsetail broth or a milk-water mixture.
Gardeners should keep in mind that the fungus can overwinter in the soil or on fallen plant parts. Therefore, thorough treatment is important, as well as regular monitoring of garden plants in the following year.
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Preventing Mildew on Cucumbers
To avoid plant diseases of any kind, the right location and good care are essential. Cucumbers should be placed in a sunny, warm, and wind-protected spot. Cucumbers–as well as other vegetable plants–should always be watered at the roots and not over the leaves.
Additionally, make sure to plant the plants with sufficient distance from each other in the bed. Choosing resistant varieties also has a preventive effect. Usually, the seed packets contain a note on good resistance to certain diseases.
Tip: Mildew is particularly common in plants from the gourd family, which includes cucumbers. Pumpkins, zucchinis, and melons should therefore not be planted in close proximity to each other to avoid infection chains.
Can You Eat Cucumbers Affected by Mildew?
An infection with mildew can cause cucumber plants to wither. However, if the infection is detected in time, the fruits can usually still be consumed–as noted by the German Environment Agency. It is important to thoroughly clean the fruits before consumption.