How To Treat Powdery Mildew On Plants

The growth potential and yield of plants are often truncated by either pests or various diseases. If you grow vegetables like cucumber, kale, or cabbage, you must be cautious about the powdery mildew disease.

As an astute gardener, you need to have a good knowledge of different plant diseases, their symptoms, how plants get these diseases, and various treatment and control measures to adopt. As you read through, you will learn how to recognize and treat powdery mildew using various techniques.

What is Powdery Mildew?

Powdery mildew is a fungal disease that affects a wide variety of plants. It is caused by many different species of fungi in the order Erysiphales. Powdery mildew gets its name from the white or gray powdery spots that appear on the leaves, stems, and fruits of infected plants. 

Powdery mildew fungi propagate through wind-blown spores. When spores land on susceptible plants, they germinate and infect the plants if there is high humidity and moderate temperatures (60-80°F). The optimal conditions for powdery mildew growth are when days are warm and dry, and nights are cool and humid.

The most common types of powdery mildew are:

  • Erysiphe cichoracearum: affects cucurbits, like squash, tomato, pepper, melons, and cucumbers.
  • Sphaerotheca macularis: affects roses, strawberries, and fruit trees.
  • Erysiphe polygoni: affects many herbaceous plants.

Powdery mildew is one of the most widespread plant fungal diseases. It affects a wide range of plants ranging from vegetables to ornamental plants like roses, fruit trees like Apple, and shrubs, who are not immune to Powdery mildew.

How To Recognize Powdery Mildew In Plants

Powdery mildew in plants
Powdery mildew in plants

Powdery mildew is one of the easier plant diseases to identify; the symptoms are distinctive. Powdery mildew usually presents first as circular, powdery white spots on leaves and stems. Infected plants appear to have powdery white spots on leaves and stems.

As the disease progresses, powdery mildew can cover the entire plant; starting from the lower leaves, stems, and fruits with a white, powdery coating. The affected plant parts then turn yellow, wither, and die.

Using Fungicides To Treat Powdery Mildew in Plants

Fungicides are chemical products designed to kill fungal diseases like powdery mildew. Several types of fungicides can be effective:

1) Sulfur: Sulfur is one of the oldest fungicides and remains very effective against powdery mildew. It comes as a dust or liquid. Sulfur works by preventing spore production. Apply according to label instructions when the first signs of mildew appear.

2) Bicarbonates: Bicarbonate fungicides like potassium bicarbonate work by changing the pH on plant surfaces to inhibit fungus growth. Apply as a foliar spray weekly starting when conditions favor powdery mildew.

3) Neem oil: Neem oil comes from the neem tree and contains azadirachtin which inhibits fungal growth. It is approved for organic gardening. Apply neem oil according to label instructions as soon as any mildew is spotted.

4) Chlorothalonil: Chlorothalonil is a common synthetic fungicide that prevents spore germination. Follow label instructions carefully regarding the timing and frequency of applications. Start applying at the first sign of powdery mildew.

5) Copper: Copper fungicides are broad spectrum and work by inhibiting enzymes needed for fungal metabolism. Buildup in soil can cause toxicity so they should be rotated with other treatments. Start applying copper fungicides weekly at initial signs of mildew.

Related: Fungicide For Plants: Types, How & When It is Used

Before using any fungicide for powdery mildew treatment, carefully read and follow the label instructions for timing, dosage, and safety precautions. Wait for the specified period before re-entering treated areas.

In addition, wear protective equipment like gloves and goggles during application to prevent skin irritation. It is advisable to rotate between fungicide types to prevent resistance. With proper application, fungicides can effectively treat powdery mildew and prevent recurring outbreaks.

Homemade/Organic Powdery Mildew Treatments

Organic treatments can be very effective at treating and preventing powdery mildew without the use of traditional fungicides. These methods utilize common household ingredients or natural oils that have antifungal properties. Some easy organic treatments to use on plants with powdery mildew include:

1) Milk Spray

Milk is popular with home gardeners and small-scale organic farmers as a treatment for powdery mildew. To use milk, mix 1 part of milk in 10 parts of water and spray on affected plants at the first sign of infection. The milk contains proteins that disrupt the fungus’s growth and prevent further spread. Reapply every 7-10 days as needed.

Milk can also be used as a preventative measure; it can be repeated weekly. It has been reported that milk’s effectiveness in treating powdery mildew is powerful as compared to some conventional fungicides, and better than benomyl and fenarimol at higher concentrations.

2) Baking Soda

Baking soda raises the pH level on plant surfaces, creating an environment that stops fungal spores from germinating. Mix 1 tablespoon baking soda with 1 quart of water. Add 1/2 teaspoon of mild liquid soap as a spreader stick. Spray leaves thoroughly. Reapply every 7-14 days.

3) Neem Oil

This is a readily available organic option to treat plant diseases and insect pest control. Neem oil is extracted from the neem tree; it is a broad-spectrum, natural pesticide that treats powdery mildew by interfering with the fungus’ metabolism and terminating spore production.

4) Mouthwash

According to Jeff Gillman, Ph.D. and Associate Professor at the University of Minnesota, Department of Horticulture, using one part ethanol-based mouthwash to three parts water worked well for powdery mildew treatment and control.  

5) Apple cider vinegar

Just like the mouthwash, the acetic acid in apple cider vinegar can treat and control powdery mildew in plants. To use, simply mix 2-3 tablespoons of apple cider vinegar, containing 5% acetic acid in a gallon of water and spray the affected plants twice daily.

Ways of Preventing Powdery Mildew

Powdery mildew can often be prevented by taking some simple precautions:

– Improve Air Circulation: Powdery mildew thrives in stagnant, humid conditions. Improve airflow around your plants by spacing them appropriately, thinning dense foliage, growing plants on trellises, and using fans indoors. Good air circulation keeps leaves dry.

– Proper Watering: Avoid overwatering and overhead watering. Water at the soil level instead of wetting foliage. Water in the morning so leaves can dry out during the day. Drip irrigation systems help provide consistent soil moisture without wetting leaves.   

– Do not overcrowd plants: Overcrowded plants trap moisture and block airflow. Use recommended spacing for each plant to be grown and prune or thin overgrown areas. 

– Remove Susceptible Plants: Some varieties are genetically prone to powdery mildew. Removing the most susceptible plants can limit the spread.

– Pruning affected areas: Prune off any leaves, stems, or branches with severe powdery mildew infestations. This helps limit its spread. Make cuts well below affected tissue and dispose of debris immediately. Avoid pruning in wet weather as it can spread spores.

– Sanitize gardening tools after each use: Make a solution of 1 part bleach to 4 parts water and dip, wipe, or spray tools after pruning or touching infected plants. This prevents transferring spores from plant to plant.

Keeping your garden free of powdery mildew inoculum through careful sanitation and cleaning practices is one of the most effective treatment and prevention methods. By taking these preventative measures, you can help reduce powdery mildew naturally without chemicals. But if it does occur, prompt treatment is key before it spreads.

Related: Cucumber Downy Mildew Chemical Control

End Notes

With consistent applications of fungicides or organic treatments, along with good sanitation practices, powdery mildew growth can be stopped and reversed. While the infected areas of leaves and stems may remain somewhat unsightly, new healthy growth will emerge after treatment. Proper maintenance and prevention measures should then be followed to avoid recurrence.


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