Mildew

Mildew: causes, prevention and treatment

Mildew is a fungal disease that affects many plants in the garden, greenhouse or living room, especially tomatoes, potatoes and onions. The top of the leaves are covered with yellow spots that grow larger and larger and eventually cover the whole leaf. A grey layer appears on the underside of the leaves, which can also have shades of purple. 

On this page, we discuss what powdery mildew is, what causes it, how to prevent it and how to treat it.

Causes of powdery mildew

Mildew is a type of fungus that grows in moist environments. It can be caused by several things, including:

• Extra moisture in the air. This can be the result of high humidity or condensation from, for example, leaking pipes or windows.
  
• Poor ventilation. If a room is not well ventilated, the moist air can promote the growth of mould.
• Dirty surfaces. If surfaces are not cleaned regularly, they can provide a place for mould spores to land and start growing.

Preventing mildew on plants 

• Avoid as much nitrogen as possible, as this promotes mildew growth
• Prune infected parts of the plant and clear away leaves that have fallen from the plant. This limits the risk of infection 
• Use salicylic acid. This improves the plant's defences
• Avoid too many air flows in the greenhouse
• Use crops that are not susceptible to mildew.
• Make sure the crop never stays wet longer than necessary and can dry, but avoid excessive air currents  
• If a plant's cell wall is strong, it becomes more difficult for fungi to invade. Adding more calcium or silicon to the nutrient regimen makes the cell walls stronger. 

Prevention of mildew in the home

Steps to prevent mildew

The best way to prevent mildew is to take some simple measures to keep your home clean and dry. Here are some tips:

• Remove spillages immediately, especially in the kitchen and bathroom.
• Don't leave wet laundry lying around. Hang it up as soon as possible or put it in the dryer.
• Use an exhaust fan when cooking or showering and open a window to ventilate damp rooms.
• Repair any leaks immediately, including leaks in pipes, roofs and around windows and doors.
• Keep gutters clean and free of debris so they can drain properly.
• If you live in an area with high humidity, use a dehumidifier (moisture absorber) to reduce the moisture in the air.

What can you do against mildew? 

If you already have mildew in your home, you need to clean it up and make sure it doesn't come back. 

Here are some tips:

• Start by cleaning surfaces with a mild detergent or a solution of soap and water. Scrub stubborn spots with a brush.
• Make sure you dry the room completely after cleaning, as mould thrives in moisture. Use a fan or heater if necessary.
• You may also need to treat the spot with an organic fungicide, such as Serenade.
  
• To prevent mildew from coming back, keep the area clean and dry. Consider using a dehumidifier if you live in a humid climate as the Netherlands generally is. 

Natural methods to treat mildew

There are a number of natural methods to treat mildew. One is to mix equal parts vinegar and water, and use this mixture to scrub the affected area. You can also mix baking soda with water to make a paste, which you can use to scrub the affected area. You can also make a solution of one part hydrogen peroxide and three parts water, and use this to scrub the affected area.

Chemical treatment of mould

There are also a number of chemical methods to treat mildew, obviously this is not our preferred method, but for completeness we want to mention it anyway. One is the use of a bleach, which can be made by mixing a cup of bleach with a litre of water. Another method is to use a commercial mould and mildew remover, available in most DIY stores.