How to Prevent and Treat Powdery Mildew on Houseplants

How do I prevent and treat powdery mildew on indoor plants?

Unraveling the mysteries of powdery mildew, a fungal menace that can plague indoor and outdoor plants alike, is a important skill for plant enthusiasts. This comprehensive guide covers the characteristics of powdery mildew, its favored hosts, and the conditions that fuel its growth. Prevention and treatment strategies are elucidated, emphasizing the importance of good cultural practices, vigilant monitoring, and timely intervention. Whether it’s promoting air circulation, moderating humidity, or employing fungicidal treatments, this guide equips plant caretakers with the knowledge needed to combat powdery mildew effectively. By adopting these measures, plant enthusiasts can fortify their indoor green havens against this common fungal adversary, ensuring the continued vibrancy and health of their cherished plants.

What is Powdery Mildew?

Powdery mildew is a fungal disease that affects a wide range of plants, both indoors and outdoors. It is caused by various species of fungi belonging to the Erysiphales order. The characteristic symptom of powdery mildew is the appearance of a white, powdery substance on the surfaces of leaves, stems, and sometimes flowers. While powdery mildew doesn’t usually cause severe harm to well-established plants, it can affect their overall health and aesthetics. Preventing and treating powdery mildew on indoor plants involves a combination of good cultural practices and, in some cases, the use of fungicidal treatments. Here are guidelines for both prevention and treatment:

Key Characteristics of Powdery Mildew

  • White Powdery Substance:
    • Powdery mildew forms a white or grayish powdery coating on the surfaces of leaves and other plant parts.
  • Leaves and Stems Affected:
    • The fungus primarily affects the upper sides of leaves, stems, and flowers.
    • In severe cases, it can spread to both sides of the leaves.
  • Leaf Deformation:
    • Infected leaves may become distorted, curled, or twisted.
    • Growth abnormalities may occur in severe cases.
  • Yellowing of Leaves:
    • Leaves affected by powdery mildew may yellow or exhibit chlorosis.
  • Reduced Plant Vigor:
    • Severe infections can lead to a decline in overall plant vigor and health.
  • Favorable Conditions:
    • Powdery mildew thrives in conditions of moderate temperatures (60-80°F or 15-27°C) and high humidity.
    • Unlike some other fungi, it can develop in conditions where free water is not present.

Common Host Plants

  • Ornamental Plants:
    • Roses, zinnias, phlox, lilacs, and many other ornamental flowers.
  • Fruit Trees:
    • Apple trees, peach trees, grapevines, and other fruit-bearing plants.
  • Vegetables:
    • Cucumbers, squash, tomatoes, and various other vegetables.
  • Herbs:
    • Basil, rosemary, and other herbaceous plants.
  • Indoor Plants:
    • Powdery mildew can also affect indoor plants, including houseplants like African violets, jade plants, and spider plants.

Prevention and Control

  • Good Air Circulation:
    • Ensure proper air circulation around plants by spacing them adequately.
  • Moderate Humidity:
    • Maintain moderate humidity levels, especially in indoor settings.
  • Avoid Overhead Watering:
    • Water at the base of the plant to keep foliage dry.
  • Regular Inspection:
    • Regularly inspect plants for early signs of powdery mildew.
  • Pruning:
    • Prune and remove infected plant parts to reduce the spread of the fungus.
  • Fungicidal Treatments:
    • Apply fungicides labeled for powdery mildew control. Follow product instructions carefully.
  • Natural Predators:
    • Introduce natural predators like ladybugs or predatory mites.


  • Proper Air Circulation:
    • Ensure good air circulation around plants by spacing them adequately.
    • Avoid crowding plants, especially in indoor settings.
  • Moderate Humidity:
    • Maintain moderate humidity levels. High humidity promotes powdery mildew.
    • Use a dehumidifier if necessary, especially in enclosed spaces.
  • Avoid Overhead Watering:
    • Water plants at the base to keep foliage dry.
    • Use a watering can or a soaker hose to apply water directly to the soil.
  • Morning Watering:
    • Water plants in the morning to allow foliage to dry during the day.
  • Remove Infected Leaves:
    • Regularly inspect plants for signs of powdery mildew and promptly remove affected leaves.
    • Dispose of infected plant material in the trash (not compost).
  • Neem Oil or Horticultural Oil:
    • Apply neem oil or horticultural oil as a preventive measure. These oils can create a protective barrier on the plant surface.
  • Sulfur-Based Fungicides:
    • Consider using sulfur-based fungicides, which are effective against powdery mildew. Follow product instructions carefully.


  • Prune Affected Parts:
    • Prune and remove severely infected leaves and branches. Dispose of the cuttings properly.
  • Water Rinse:
    • Rinse the affected leaves with water to remove some of the powdery mildew spores.
    • Repeat this process regularly.
  • Baking Soda Solution:
    • Mix a solution of 1 tablespoon of baking soda, 1/2 teaspoon of liquid soap, and 1 gallon of water.
    • Spray affected plants with this solution every 7-14 days. Be cautious with sensitive plants.
  • Milk Spray:
    • Mix a solution of 1 part milk (cow’s milk is commonly used) and 9 parts water.
    • Spray the mixture on affected plants every 7-14 days.
  • Fungicidal Soaps:
    • Apply fungicidal soaps or potassium bicarbonate-based fungicides. Follow product instructions for application.
  • Biological Control:
    • Introduce natural predators like ladybugs or predatory mites, which can feed on powdery mildew.
  • Commercial Fungicides:
    • Use commercial fungicides labeled for powdery mildew treatment. Follow product instructions carefully.

General Tips

  • Monitor Regularly: Regularly inspect your plants for early signs of powdery mildew, especially in areas with poor air circulation.
  • Quarantine New Plants: Inspect new plants before bringing them indoors to prevent introducing powdery mildew.
  • Rotate Plants: If possible, rotate the position of your plants to prevent the recurrence of powdery mildew.
  • Improve Ventilation: Use fans to improve air circulation around indoor plants.


In conclusion, understanding and addressing the challenges posed by powdery mildew are essential for maintaining the well-being of indoor plants. This comprehensive guide provides insights into the characteristics of powdery mildew, its potential hosts, and practical strategies for prevention and treatment. Powdery mildew is a common and widespread fungal disease, but with proper preventive measures and timely treatment, its impact on plants can be minimized. Early detection and intervention are key to effectively managing powdery mildew and preserving the health of affected plants. Powdery mildew can be challenging to eradicate completely, so early detection and prevention are crucial. Consistent monitoring, good hygiene, and a combination of preventive measures can help keep your indoor plants healthy and free from powdery mildew. By embracing good cultural practices, fostering vigilant monitoring, and employing timely interventions, plant caretakers can safeguard their green companions from the detrimental effects of this fungal intruder. Armed with this knowledge, enthusiasts can create resilient indoor environments, fostering flourishing plants that stand resilient against the threat of powdery mildew.

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