What Do White Spots On Cucumber Leaves Mean? (Your Guide To Powdery Mildew)

What Do White Spots On Cucumber Leaves Mean (Your Guide To Powdery Mildew)

Have you noticed white spots on your cucumber leaves and don’t know what they are? Maybe you have heard the phrase powdery mildew and want to know if this is the issue?

Or are you curious and want to know more? No matter the reason that brought you here today, we have the answer for you. 

Finding out what white spots on your cucumber leaves mean can be tricky, especially if you have never had them before.

You head online to find out more but are met with page after page of conflicting and confusing answers.

You are left frustrated and overwhelmed, unsure who to trust or where to turn, while your leaves get more and more spots. 

What are you supposed to do?

Well, you can turn to us for the answers you need! White spots on your cucumber leaves are usually a sign of powdery mildew, fungi that can wreak havoc in your garden.

Keep reading to learn more about powdery mildew and how you can protect your cucumbers! 

What Is Powdery Mildew?

Powdery mildew is a fungal disease that affects a variety of plants.

There are many different species of powdery mildew, but the two that impact cucumbers the most are Erysiphe cichoracearum and Podosphaera fuliginea. 

Powdery mildew will appear as white powder spots on cucumber leaves. It will look similar to white mold. These spots will expand over a wide area, covering leaves and branches.

Not only will powdery mildew spread quickly, but it can infect your entire plant, leaving you with yellow and wilting leaves. In extreme cases, the cucumbers your plant is growing can die! 

Now that we have established what powdery mildew is, let’s dive in a little deeper to learn more about powdery mildew. 

What Causes Powdery Mildew?

What Do White Spots On Cucumber Leaves Mean? (Your Guide To Powdery Mildew) 1

Several factors can cause powdery mildew to appear on your cucumber leaves.

These are all environmental factors that you should be aware of when growing cucumber plants, check out our list of these factors below.

  • High humidity
  • Shady conditions
  • Temperatures between 60 and 80 degrees Fahrenheit 
  • Cool nights with temperatures below 55 degrees Fahrenheit
  • Excessive moisture 
  • Dense plant growth with poor air circulation 

If your cucumber plants are stressed, they are more susceptible to powdery mildew and other common diseases.

How To Treat Powdery Mildew On Cucumbers 

If you spot white spots on your cucumber leaves, you must act right away. There are a few ways that you can treat powdery mildew, giving you plenty of options to choose from.

Let’s take a look at them now to help you find the best option for you. 


First, you can use fungicides. Fungicides can treat your white spots on cucumbers providing that you catch them early. Fungicides work to prevent the fungal spores from germinating. 

There is a range of fungicides you can choose from, but you must make sure it is appropriate to use on cucumbers for powdery mildew.

You need to use fungicides consistently and in line with the directions on the label. Otherwise, it won’t be effective and the powdery mildew will return. 

Organic Treatments 

If you don’t want to use chemicals, try an organic treatment. There are a few treatments you can try. A popular one is using a mixture of water and baking soda. Mix one tablespoon of baking soda with a gallon of water. 

Spray the mixture on both sides of the leaves on your cucumber plant. The baking soda will raise the pH levels in your plants’ leaves, making it harder for the fungus spores to survive.

Powdery mildew thrives in an acidic environment, so this treatment will work wonders! 

You can also try using milk. Mix one part milk with nine parts of water. Spray the mixture on your cucumber plants.

No one knows why, but this treatment makes it harder for powdery mildew to grow and can be as effective as fungicides. 

Repeat this treatment every five to seven days until the white spots are gone. 

Remove The Cucumber Plant

Sometimes there are no other options but to remove the cucumber plant. Usually, when the plant is severely infected with powdery mildew or other diseases.

Remove any leaves that have fallen off the plant as these can contain spores that could spread to other plants. 

You should also avoid planting any new cucumber plants in the same spot the infected plant was. There might be some fungus spores in the soil that could spread to any new plants. 

Preventing Powdery Mildew On Cucumbers 

Once the white spots are removed, you need to prevent them from coming back.

There are a few steps you can follow to prevent powdery mildew from covering the leaves on your cucumber plants! 

Check out your options below! 

Pick Disease Resistant Varieties 

The easiest way to prevent plant diseases is to plant mildew-resistant cultivators.

There are varieties of plants that have been bred to resist powdery mildew and other diseases, meaning you don’t need to worry about them when you grow cucumber plants. 

When purchasing cucumber plants, opt for varieties that are resistant to powdery mildew. How will you tell which ones are resistant?

There will be PM listed on seed packets, indicating that these are resistant to powdery mildew. We recommend purchasing these when planting cucumber seeds. 

Look out for the following, which are all resistant to powdery mildew: 

  • Ashley 
  • Cool Breeze F1
  • Diamondback 
  • Hybrid 177 
  • SV3462CS 

You can also find some pickle cucumber varieties that are resistant to powdery mildew. These include:

  • Adam Gherkin F1 
  • Gherkin F1
  • Picklebush 

These aren’t exhaustive lists, but give a good indication of the seeds you can choose from if you want to plant seeds that are resistant to powdery mildew. 

Improve Air Circulation

Another option is to improve air circulation. As we mentioned earlier, powdery mildew thrives in high humidity.

You can reduce the chances of your cucumbers getting powdery mildew if you increase the air circulation around young plants. 

When you are preparing to plant your cucumbers, ensure that your plants will have enough room.

They need to have space to grow without touching or overlapping each other. Cucumbers can take up a lot of space, especially bush varieties.

Plant your cucumber seeds six inches apart. Once they grow into seedlings, thin out the cucumber plants so they aren’t touching each other.

It is better to plant them further apart than needed, rather than to plant them too close together. 

You can also improve air circulation by pruning your cucumber plants. Remove any dying or dead leaves as they can harbor fungus spores.

You can also avoid getting the leaves wet when watering the cucumbers. This can also promote powdery mildew, so keep water off your leaves where you can! 

Improving your air circulation will reduce the chances of powdery mildew growing or returning. 

Plant Cucumbers In Full Sun

You can prevent powdery mildew if you plant your cucumbers in an area that gets full sun. cucumber plants need at least eight hours of sunlight a day to keep powdery mildew at bay.

If you live in an area with hot summers, plant your cucumbers in an area that gets some afternoon shade. This stops the leaves from getting scorched by the sun. 

Direct sunlight is vital to prevent powdery mildew on cucumbers. Why? Well, direct sunlight evaporates any moisture on the leaves.

If the leaves are wet for too long, it can be the ideal environment for powdery mildew to grow. 

The fungal spores need moisture to germinate. If the leaves are wet, it provides the perfect condition for the spores to germinate.

Sunlight makes it harder for the powdery mildew spores to survive, so you must pay attention to the bottom leaves of your cucumber plant.

These leaves are most likely to stay wet and be shaded by the sun. White spots on your cucumber leaves will most likely start at the bottom and work their way up your plant.

Regularly inspect your cucumber plant and the bottom leaves, removing any affected leaves. 

Water Cucumbers In The Morning 

Another way to prevent powdery mildew from spreading is to water your cucumber plants in the morning.

Doing so ensures that your leaves have time to dry before night, eliminating the chance of powdery mildew growing. 

If you water your cucumbers in the evening, when the weather is cooler, the leaves will stay wet overnight. This creates the perfect environment for powdery mildew to grow, something you don’t want! 

When watering your cucumbers, opt for a drip irrigation system or a soaker hose. This helps to keep the leaves of the cucumber plant dry as the water will go directly to the roots of the plant. 

Don’t water your cucumbers from above. The leaves can stay wet when you do, causing powdery mildew. Water your plants from the base, rather than above, getting the water to the roots quickly. 

Make sure that you are watering your cucumbers deeply but less often. Deep watering encourages the roots of the plant to grow deeper into the ground.

This makes your plant less likely to suffer from drought stress. Drought stress can make your plant more susceptible to powdery mildew, so you want to avoid this where possible! 

Make sure that you are watering your cucumber plants directly from the bottom in the morning and have planted them where there is enough direct sunlight for the leaves to dry, reducing the chance of powdery mildew. 

Final Thoughts 

And there you have it! White spots on cucumber leaves are typically powdery mildew, a fungus that impacts plants.

The white spots are similar to white mold and can spread across the leaves and branches, killing the cucumber plant if left untreated. 

But when you spot these white spots, it isn’t all bad news.

There are a few treatments you can try, including chemical treatments, organic homemade remedies, and removing the cucumber plant when the mold has spread too far. 

Once you have cleared the white spots from the plant, you can use the methods listed to prevent powdery mildew from returning.

These include planting your cucumber seeds far enough apart, watering them during direct sunlight, improving air circulation, or planting varieties of cucumber that are powdery mildew resistant. 

With a little extra care and some time spent planting your cucumbers in the right spot, you can grow healthy cucumber plants that won’t be impacted by powdery mildew! 

Frequently Asked Questions 

Before you leave, be sure to check out our brief FAQ section to get the answers to your last-minute questions!

What Is The Main Cause Of White Spots On Cucumber Leaves?

Powdery mildew is the main cause of white spots on cucumber leaves.

How Does Powdery Mildew Spread?

Powdery mildew can spread in a few ways, mainly water droplets, soil unclean tools, wind, and insects.

Why Are Cucumber Leaves Turning White After Transplant?

Your cucumber leaves might turn white after transplant due to cucumber transplant shock.

How Can I Disinfect Tools Use To Remove Plants With Powdery Mildew?

The best way to disinfect tools used to remove powdery mildew is to wipe them with a solution that is one part bleach to nine parts water.

Use this solution after every use to prevent powdery mildew from spreading to your other plants and soil!

About The Author

Gina Harper grew up dreaming about farms and growing her own food. She began an urban garden to feed herself and turned it into an incredible hobby. Gina is here to teach you everything from raised beds to container gardening, how to keep plants alive and well in a smoggy city, and the works. It’s time that we carve our own piece of green earth and reap what we sow—she’s here to help you with that.