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Cucumber Leaves Turning White: How to Deal with Powdery Mildew 

Why Cucumber Leaves Turning White

Your cucumber leaves turning white could signify powdery mildew, a common fungal disease that can harm your cucumber plants. 

But don’t worry; there are effective ways to deal with this pesky problem and save your cucumbers. In this article, we’ll delve into powdery mildew, exploring its causes, symptoms, and, most importantly, how to combat it. 

From natural remedies to commercial fungicides, we’ll provide you with the knowledge to protect your cucumber plants and ensure a bountiful harvest. So, if you’re ready to say goodbye to powdery mildew and hello to healthy, thriving cucumbers, keep reading!

What is powdery mildew?

What is powdery mildew
Image: Plantura

Powdery mildew is a fungal disease commonly found throughout North America that affects cucumber plants. It is caused by a fungus called Podosphaera xanthii, which leaves unsightly white spots on cucumber leaves. 

From afar, these white spots look like white mold. In reality, they are tiny white spots that develop on the leaf surface, stems, flowers and fruits of the cucumber plant and gradually expand over a wide area of the leaves and branches.

The fungus can spread quickly and infect the entire plant if left untreated. It can cause the leaves to turn yellow and wilt, significantly reducing the plant’s yield and overall health, and can even cause the cucumber plant’s death.

What are the symptoms of powdery mildew?

What are the symptoms of powdery mildew
Image: Plantura

Symptoms of powdery mildew include white powdery spots on the leaves of cucumber plants. These spots start to enlarge, leading to yellowing and wilting of the leaves, stunted growth, reduced yield, and fruit discoloration.

It almost looks like a child sprinkled flour on the plant in the early days of the fungal disease. Visible symptoms can appear at any time in the growing season, but they tend to be more pronounced when there are sudden changes in temperature and humidity.

How does powdery mildew spread?

How does powdery mildew spread
Image: Plantura

Powdery mildew spreads primarily through the wind. The fungus produces lightweight spores easily carried by air currents, allowing the disease to spread rapidly to neighboring cucumber plants and other garden plants. 

Splashing water from overhead irrigation or rain can also spread these spores. If the infected plant debris is not properly disposed of, it can harbor the fungus and spread it to other plants when the debris is moved or comes into contact with healthy plants.

Contaminated tools, hands, or clothing can also transfer spores from an infected plant to a healthy one. This is why sanitizing tools and equipment after working with infected plants is essential to avoid spreading their disease to the healthy ones. 

What causes powdery mildew?

What causes powdery mildew
Image: University of Minnesota Extension

Powdery mildew is caused by a fungus called Podosphaera xanthii that thrives in warm, dry conditions with low air circulation. It produces spores that are easily spread by the wind.

Powdery mildew fungi thrive in temperatures between 65 and 85 degrees Fahrenheit and low humidity conditions. 

For instance, densely planted cucumber plants or those grown in shaded areas with poor air circulation are more susceptible to powdery mildew infection. 

Similarly, excessive nitrogen fertilization can promote lush foliage growth, creating a favorable environment for powdery mildew fungi to develop.

Will other plants get infected by powdery mildew from cucumber plants?

Will other plants get infected by powdery mildew from cucumber plants
Image: The Seed Collection

The fungus that causes powdery mildew on cucumber plants can also infect other cucurbits like melons, squash, pumpkins, grapes, roses, and ornamentals.

Some nightshades, such as potatoes, tomatoes, and eggplants, and flowering plants, such as begonias and roses, are also sensitive to the same disease.

Many plant growers make a huge mistake and grow these plants in the same medium after they remove the affected cucumbers. Remember that fungi can also thrive in soil, so you won’t destroy it by taking the plant out.

How to Treat Powdery Mildew on Cucumbers

Treating cases of powdery mildew is fairly straightforward. Let’s look at these effective ways to treat powdery mildew on cucumbers.

1. Prune the affected plant.

Prune the affected plant
Image: Better Homes and Gardens
DifficultyEasy ●○○○○
Duration30 to 45 minutes
Things You NeedPruning shears
Garbage bag

Pruning is an essential gardening practice in controlling powdery mildew on cucumber plants. It also helps improve air circulation, which keeps the leaves dry and makes them less likely to be a breeding ground for the fungus. 

When 50% of the leaf is covered with mildew, prune them immediately. Removing the infected leaves will reduce the fungal spores and make the disease less likely to spread to the other parts of the plant. 

How To Do
1. Sterilize the pruning shears with alcohol.
2. Always use sterilized pruning shears to cut the leaves at their base so you don’t leave any infected tissue behind.
3. Start by removing all severely infected leaves.
4. If the powdery mildew has spread to the stems or fruits, carefully prune away the infected parts. 
5. After pruning, thoroughly sanitize your pruning shears or scissors with rubbing alcohol or a bleach solution to prevent the spread of the fungus.
6. Place all infected plant material in a sealed bag or container and dispose of it properly. 
7. Do not add infected plant material to your compost because this can spread the fungus to other plants in your garden.

2. Apply neem oil solution.

Apply neem oil solution
Image: Gardenia
DifficultyEasy ●○○○○
Duration30 to 45 minutes
Things You NeedNeem oil
Spray bottle
Mild soap

Neem oil is also an effective solution when treating cucumber plants for powdery mildew. It’s a natural fungicide derived from the seeds of the neem tree and effectively controls powdery mildew on the infected plant.

Neem oil disrupts the fungus’s life cycle, preventing it from reproducing and spreading. It can also deter predatory insects like lacewings. 

However, if you spray, make sure to do so when no pollinators are around since they can be harmed if hit directly. 

Avoid applying neem oil solution to the cucumber plant in direct sunlight, which can cause leaf burn. Instead, we recommend applying it early in the morning or late in the evening.

How To Do
1. Combine one tablespoon of neem oil in a spray bottle with one gallon of water. 
2. Add a few drops of mild soap to help the oil adhere to the leaves.
3. Spray the neem oil solution generously on all surfaces of the cucumber plants, including the leaves, stems, and fruits.
4. Be sure to coat the undersides of the leaves where powdery mildew is most likely to develop.
5. Allow the neem oil solution to dry completely for about 24 hours.
6. Repeat the application every 7 to 14 days until the powdery mildew is gone.

3. Apply fungicides.

Apply fungicides
Image: North Carolina Extension
DifficultyEasy ●○○○○
Duration30 to 45 minutes
Things You NeedSulfur or potassium carbonate fungicide
Spray bottle

Fungicides can be used to treat the white spots on cucumbers as they can effectively prevent the fungi spores from germinating and spreading to the cucumber plant and other plants in your garden. 

Sulfur and potassium carbonate are the most commonly used fungicides targeting white spots on cucumber leaves. It’s available in both dust and liquid formulations, and you can simply apply the formula once every week on your cucumber plant. 

How To Do
Choose the appropriate fungicide. 
Sulfur is a more effective fungicide for powdery mildew but can harm plants in hot or humid conditions. Potassium carbonate is a safer option for use in warmer climates.

Mix the fungicide solution.
For sulfur, mix 1 to 2 tablespoons of sulfur per gallon of water. Mix 1 to 2 teaspoons of potassium carbonate per gallon of water for potassium carbonate.

Spray the fungicide solution.
Spray the solution on all surfaces of the cucumber plants, including the leaves, stems, and fruits. Coat the undersides of the leaves, as this is where powdery mildew is most likely to develop.

4. Apply milk solution to the cucumber plant. 

Apply milk solution to the cucumber plant
Image: Pinterest
DifficultyEasy ●○○○○
Duration30 to 45 minutes
Things You NeedMilk Water
Spray bottle

A milk solution is a simple and effective home remedy for treating powdery mildew on cucumber plants. 

Milk contains proteins and lactic acid that have antifungal properties for controlling the growth of powdery mildew fungus. This treatment should be repeated every five to seven days until the white spots are gone.

How To Do
1. Combine one part of milk in a spray bottle with nine parts of water. 
2. Shake well to mix the solution thoroughly, and spray the milk solution on the cucumber plants. 
3. Allow the milk solution to dry completely and repeat the application every 7 to 14 days or until the powdery mildew is gone.

5. Spray a baking soda solution.

Spray a baking soda solution
Image: Backyard Boss
DifficultyEasy ●○○○○
Duration30 to 45 minutes
Things You NeedOne tablespoon of baking soda
1/2 teaspoon liquid non-detergent soap
1-gallon water
Spray bottle

Baking soda is another naturally occurring compound with antifungal properties that can control powdery mildew on cucumber plants. 

It works by raising the pH level of the plant’s surface, making it less hospitable for the fungus to thrive. We recommend applying this on your plants when temperatures are below 85 degrees Fahrenheit.

How To Do
1. Combine one tablespoon of baking soda, 1/2 teaspoon of liquid non-detergent soap, and 1 gallon of water in a spray bottle.
2. Shake well until the baking soda is completely dissolved.
3. In the early morning or late evening, spray the baking soda solution onto all surfaces of the cucumber plants, including the underside of the leaves, stems, and fruits. 
4. Allow the solution to dry completely.
5. During this time, avoid watering the plants to allow the solution to adhere properly.
6. Monitor the plants regularly to check for signs of powdery mildew.
7. If the mildew persists, re-apply the solution every 7 to 14 days until the mildew is gone.

6. Cover the cucumber plant.

Cover the cucumber plant
Image: Iowa State University

Covering the affected cucumber plant is a simple and effective method to prevent the spread of powdery mildew and promote the recovery of the plant.

Covering the plant creates a humid environment unfavorable for the powdery mildew fungus to thrive. It also ensures that wind currents will not easily carry the infected spores toward other healthy plants. 

You can place a lightweight, breathable fabric like cheesecloth, muslin, shade cloth, or row covers on cucumber seedlings to deter larger pests like leafhoppers.

7. Spray a garlic solution on the cucumber plant. 

Spray a garlic solution on the cucumber plant
Image: Food Revolution
DifficultyEasy ●○○○○
Duration30 to 45 minutes
Things You Need2-3 medium-sized garlic bulbs
1 gallon of water
Unbleached cheesecloth or coffee filter
Spray bottle

Garlic, a common kitchen ingredient, has antifungal properties that can be harnessed to treat powdery mildew on cucumber plants. Garlic solution is a natural and eco-friendly alternative to chemical fungicides, making it a popular choice among organic gardeners. 

How To Do
1. Peel and mince the garlic bulbs using a knife.
2. Transfer the minced garlic to a clean container and add 1 gallon of water.
3. Cover the container and let the mixture soak for 24 hours.
4. Strain the garlic mixture through unbleached cheesecloth or a coffee filter and transfer it to a spray bottle.
5. In the early morning or late evening, shake the spray bottle well to ensure the garlic solution is evenly distributed and spray the garlic solution onto all surfaces of the cucumber plants, including the leaves, stems, and fruits. 
6. Allow the garlic solution to dry completely, and avoid watering the plants during this time.
7. Inspect the cucumber plants regularly to check, and if the mildew persists, re-apply the solution every 7 to 14 days until the mildew is completely gone.

How to Prevent Powdery Mildew on Cucumbers

As they say, prevention is always better than cure. So, here are our proven and tested tips to prevent powdery mildew from infecting your cucumber plants.

1. Plant cucumbers in a sunny location.

Plant cucumbers in a sunny location
Image: Homestead and Chill

Powdery mildew thrives in shaded areas, so if your cucumber plants are in an area without enough direct light, they’ll be more susceptible to the disease.

Cucumbers need at least 6 hours of direct sun each day. More specifically, southern exposure is the gold standard for this sun-loving vegetable, where they receive light most of the day but are protected from the strongest afternoon sun.

2. Provide adequate space between cucumber plants.

Provide adequate space between cucumber plants
Image: Garden Eco

Correct plant spacing is crucial to having a healthy garden. It provides proper air circulation, making it difficult to become a breeding ground for fungal spores like powdery mildew. 

So, when planting cucumber seeds, we recommend spacing them 6 inches apart. Once they grow into seedlings, thin out the cucumber plants so they’re not touching each other. 

Additionally, if you’re companion planting other herbs, flowers, or veggies near your cucumbers, make sure there’s enough space for them so far apart that the air can still move freely, and they won’t compete with nutrients from the soil.

3. Water cucumber plants directly on the roots.

Water cucumber plants directly on the roots
Image: Sow Right Seeds

Wet leaves are a prime breeding ground for fungal diseases like powdery mildew. These fungal spores also freely land on those moist leaves and set up shop immediately.

One of the easiest ways to transmit the powdery mildew to a healthy plant is by water splashing back to the undersides of the leaves after it hits the soil, which carries the spores from the soil directly to the leaves. 

To avoid this kind of splashback, practice the following good watering habits in your garden. Water the cucumber plant directly onto its roots.

A drip system or soaker hose is the ideal way to water your plants, but if you don’t have access to them, you can turn your hose to a low setting and let the water slowly stream into the soil.

Watering this way will allow your plants to take up more water and prevent the splashback you find when using a harder spray nozzle and a fast stream of water.

4. Apply mulch around the base of the cucumber plant.

Apply mulch around the base of the cucumber plant
Image: Epic Gardening

Mulch aids moisture retention in the soil and prevents water splashing back, which, as we now know, can spread fungal disease from the soil. 

You can use many things, such as mulch, including organic material found in your yard or coconut coir. No matter what mulch you choose, apply a 2 to 3-inch thick layer for maximum benefit.

This layer of mulch will not only protect your cucumbers from splashing back from regular watering but also protect them during heavy rain.

5. Use disease-resistant varieties.

Use disease-resistant varieties
Image: Epic Gardening

If you know your area is prone to cases of this fungal disease, you may opt for a disease-resistant cucumber variety. This is the easiest way to prevent the disease from taking hold of your plants.

These varieties include the Ashley, Diamondback or Bodega, Adam Gherkin and Picklebush cucumber varieties. Some pickle cucumber varieties resistant to powdery mildew are Adam Gherkin F1, Gherkin F1, and Picklebush.

6. Prune cucumber plants regularly.

Prune cucumber plants regularly
Image: Gardening Channel

You can reduce the chances of your cucumber plants getting powdery mildew by increasing air circulation around the young plants.

Remove any dead or dying leaves when pruning, as these can harbor fungus spores. It’s also a good idea to avoid getting the leaves wet when watering the cucumbers, as this can also promote the growth of powdery mildew.

7. Practice companion planting.

Practice companion planting
Image: Epic Gardening

Companion planting is growing certain plants together for beneficial effects. In the case of cucumbers, many great companion plants can help improve their growth, flavor, and overall health. 

Legumes such as peas, beans, and lentils fix nitrogen from the air and add it to the soil, benefiting cucumber plants. On the other hand, corn can be used as a natural trellis for cucumber vines, which can help to save space and improve air circulation.

Additionally, you can plant cucumbers near chamomile as a companion plant. Chamomile repels pests that frequently attack cucumbers and enhances the growth and taste of cucumber plants.


Can plants recover from powdery mildew?

Plants can recover from powdery mildew. Proper treatment and care allow plants to overcome this fungal disease and grow and produce healthy fruits and vegetables.

Why are cucumber leaves turning white after transplant?

Cucumber leaves turn white after transplant because of excessive stress from moving from one place to another. During this time, its root system is likely more susceptible to diseases like powdery mildew, which causes white powdery spots on leaves.

Does soapy water get rid of powdery mildew?

Soapy water can be effective in controlling powdery mildew in its early stages. However, it is not a cure-all and may not be effective for severe infections.

Can cucumber leaves infected with powdery mildew be composted?

Cucumber leaves infected with powdery mildew should not be composted. The fungus can survive in compost and spread to other plants. Infected leaves should be disposed of in the trash or burned. 

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