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Causes and Solutions to White Spots on Cucumber Leaves

Cucumber plants are a popular addition to many home gardens, but they can encounter issues that affect their leaves' health and appearance. One common problem is the development of white spots on cucumber leaves. Whenever you see these white spots crawling over the leaves, a big chance is that it’s caused by powdery mildew, though in a few cases, it might also be infected with certain pests. 

In the following content, we’ll dive deeper and see what’s to blame for white spots on plant leaves. More importantly, you’ll know how to treat it properly to rescue the cucumber. 

Table of Contents

What Causes Powdery Mildew on Cucumber Leaves 

In case you don’t know, powdery mildew is a common fungal disease that affects many plants, including cucumber leaves. It is characterized by the development of white, powdery spots or patches on the upper surfaces of leaves, stems, and sometimes even fruit. 

Here's a thorough explanation of what causes powdery mildew on cucumber leaves:

Fungal Pathogen

Powdery mildew on cucumber leaves is primarily caused by fungal pathogens belonging to the genera Podosphaera and Golovinomyces. These fungi are obligate parasites, meaning they rely on living plant tissue to grow and reproduce.

Powdery Mildew

High Humidity

Powdery mildew thrives in moderate to high humidity levels, typically in the range of 40% to 100%. The fungus does not require free water on plant surfaces, making it different from many other fungal diseases.

Moderate Temperatures

The optimal temperature range for powdery mildew development is between 60°F and 80°F (15°C to 27°C). It can occur in slightly cooler or warmer conditions, but growth is slowed outside this range. If you are growing plants in a grow tent, the grow room temp and humidity can play a vital role. 


Cucumber plants are particularly susceptible to powdery mildew, especially if they are grown in conditions that promote the disease. Varieties with dense foliage and those planted too closely together may also be more prone to infection due to reduced air circulation. So, maybe it’s not your fault but the species is being bad. 

How to Treat Powdery Mildew

After diagnosing powdery mildew, remedies to fix the white spots on cucumber leaves include the following: 

Utilize Fungicides

Employ fungicides specifically designed for controlling powdery mildew. When using fungicides, follow the manufacturer's recommendations and guidelines for application. Fungicides can help reduce fungal growth and halt the spread of the disease. However, if you opt for more organic approaches to cure the cucumbers, the following alternatives are worth considering: 

  • Mix the baking soda and water to create a solution. Spray this mixture on both sides of the cucumber plant's leaves. The baking soda raises the leaf's pH levels, creating an environment less conducive for powdery mildew spores to thrive.
  • Create the milk-water mixture and spray it onto your cucumber plants. Studies suggest that this treatment can hinder the growth of powdery mildew and can be as effective as fungicides. Repeat this treatment every five to seven days until the white spots are no longer visible.
  • Neem oil is a natural and organic option for managing powdery mildew. It can be effective in reducing fungal growth when applied according to instructions.

Pruning and Removal

Remove Infected Leaves: When powdery mildew is detected, you should promptly remove infected leaves or plant parts. This not only helps reduce the spread of the disease but also improves the plant's overall health.

Additionally, prune or thin out dense foliage to improve air circulation within the cucumber plants. This can deter the development and spread of powdery mildew.

You May Also Be Interested in: How to Prune to Increase Yield

How to Prevent Powdery Mildew 

It’s hard to revert white spots back to green. Still, there’s always something you can do to prevent it from happening again to your cucumber plants.  Here are some effective strategies to prevent powdery mildew:

Plant Spacing

Proper spacing between cucumber plants is crucial. Adequate spacing allows for better air circulation, which can decrease humidity levels around the plants and inhibit powdery mildew development.

Proper Watering

Water your plants in the morning to allow the foliage time to dry during the day. Avoid overhead watering, as wet leaves can promote the growth of powdery mildew. Besides, you may want to consider using drip irrigation or soaker hoses to water your plants at the soil level. This method keeps the foliage dry and reduces moisture on leaves.

Mulch Your Cucumber Plants

Apply a layer of organic mulch, such as straw or wood chips, around the base of your plants. Mulch helps maintain consistent soil moisture and prevents soil from splashing onto leaves.

mulch plants

Bonus: Is It Safe to Eat Powdery Mildew Cucumbers

Cucumbers from plants with powdery mildew are generally safe to eat. Powdery mildew primarily affects the leaves, stems, and sometimes the fruit's outer surface, but it does not typically penetrate the interior of the cucumber. So yes, you can eat the cucumber and not get poisoned. 


White spots on cucumber leaves can be caused by a variety of factors, including diseases, pests, and environmental stress. Identifying the specific cause is crucial for implementing the right solution. Regular inspection, proper care, and timely action can help keep your cucumber plants healthy and productive. If problems persist, consider seeking advice from local gardening experts or extension services to tailor your approach to your specific growing conditions.

One thought on “Causes and Solutions to White Spots on Cucumber Leaves

  1. Douglas Walworth says:

    Thank you, that was very informative.

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