Controlling Powdery Mildew

Powdery mildew is a common fungal disease in many indoor and outdoor gardens. It can affect many plants, reducing your flowers and fruit quality and quantity. Read on to find out about controlling powdery mildew.

What is the Powdery Mildew Disease in Plants?

There are numerous powdery mildew species, and each one attacks a diverse range of plants. Commonly impacted species include:

Cucurbits, like:

  • Squashes
  • Pumpkins
  • Melons
  • Cucumbers

Nightshades, like:

  • Tomatoes
  • Aubergines
  • Peppers.

Legumes, like:

  • Beans
  • Peas

Powdery Mildew will slow plant growth. If the infection is extreme, it’ll reduce fruit yield and quality. Mildew infections show as a white layer on the top of leaves. Mildew is made up of thousands of tiny spores. The spores are easily transmitted to other plants by contact transfer or on the wind.

Beware, if you’ve had a powdery mildew “attack” in the past. Make sure you deep clean after any issues with Mildew. New mildew outbreaks may be caused by dormant spores in old vegetative or organic matter.

Image of Powdery Mildew on Tomato leaf

Powdery Mildew Symptoms, Treatment and Control

Powdery Mildew materialises as light grey or white powdery spots, found on the top of leaves. It can also be found underneath leaves or on stems, flowers, fruit or vegetables. If left untreated, the spots will spread over most of the plant. New growth is most susceptible.

Powdery Mildew flourishes in warm, dry climates. It requires high humidity. Inadequate light and poor air circulation also contribute to powdery mildew conditions.

Rarely fatal, but if left uncontrolled, mildew can severely harm plants. It deprives them of nutrients and water. Most infections cause nominal damage, with issues, like: yellowing, withered or distorted plants. Plants can also become weak, fail to flower, and suffer stunted growth.

How to Identify Mildew Damage

When Powdery Mildew strikes, your plants look as if they have a dusting of flour. Other symptoms of powdery mildew can show as:

  • Starting as circular, fine white spots on leaves, stems, and sometimes fruit.
  • Most commonly found covering the upper part of the leaves, but may grow on the undersides.
  • Young foliage is most sensitive to damage. The leaves can yellow and dry out.
  • The fungus might force some leaves to twist, break, or become deformed.
  • Eventually, the white spots will spread and cover most leaves.
  • The leaves, buds, and growing tips will all become deformed if left untreated.

Mildew Problems in the Grow Room

The Powdery Mildew fungus appears to love the moderate temperatures of grow room conditions. If you don’t stay on top of your grow room environment, you can invite it in.

Avoid these common mistakes to limit your chance of problems:

  • Poor Air Circulation and overcrowding your grow room. Use a MaxiFan clip-on fan to move air around.
  • Low light conditions are one of the most common causes of problems.
  • Powdery Mildew targets new plant growth first. Giving plants too much fertiliser may cause them to bolt (grow too quickly), which can weaken the plant and cause an outbreak of powdery mildew.
MaxiFan clip-on fan for air movement

How to Prevent Powdery Mildew

As with all pests and diseases, proactive prevention is the best means of controlling Powdery Mildew. 

  • Choose species that are resistant to mildew. Many mildew-resistant varieties have been developed. You can purchase them from major seed suppliers.
  • Plant in sunnier spots or try and keep light spread very even. Mildew tends to prefer shady areas.
  • Prune congested areas to increase air circulation around your plants; this helps to reduce relative humidity.
  • Keep plants evenly spaced to isolate any infections and reduce the risk of the fungus spreading as quickly.
  • Use an air ventilation system or fans to promote healthy air circulation.
  • Ensure your grow light timers are set accurately to give plants enough light.
  • Carefully monitor your delivery of nutrients to keep plants growing steadily and reduce the risk of infection.
  • If you experience issues, use a bleach/water solution or product like Liquid Oxygen to clean your grow room. To avoid mildew issues, best practice is to clean after each harvest or three months.
Liquid Oxygen Peroxide cleaner oxygen enhancer

How to Control Mildew 

Spraying Powdery Mildew treatment

Powdery mildew is difficult to eradicate when plants are heavily infected. Focus your efforts on preventing it from spreading to your other plants. Use a small pressure sprayer or larger pressurised sprayer to apply any treatments to ensure the best coverage.

  • Remove and destroy all infected foliage, stems, and fruit. Do not compost any of the infected plant matter. Mildew will spread through composted materials.
  • After pruning the infected parts, sterilise your pruners with rubbing alcohol.
  • Organic fungicide treatments include: sulphur, lime-sulphur, neem oil, and potassium bicarbonate. Effective when used as a preventative measure when you first spot a problem.
  • Baking soda is an effective treatment mildew. Mix one teaspoon baking soda in 250ml of water and spray your plants exhaustively. Bear in mind that this treatment will only kill any fungus that it physically comes into contact with.
  • Milk spray is an effective DIY remedy for mildew. Dilute milk with water at a 1:10 ratio and spray at the first sign of infection or as a preventative measure

What is the Importance of Plant Disease Diagnosis?

Diagnosis is essential. Without correctly identifying the disease, we cannot treat it appropriately. Using incorrect disease control measures wastes time and money. It leads to plant loss and spreads the infection. Proper plant disease diagnosis is vital. If you are uncertain about the problem, always seek a second opinion.

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