Understanding Mildews


Powdery mildew, species Podosphaera fusca

Powdery mildew, species Podosphaera fusca

Fungus and mildews are always a problem during humid weather. Understanding how they grow can help when you are trying to control them. Fungi are often visible to the naked eye and are often named for their appearance.Powdery mildew is a group of related fungi, usually showing as whitish spots on leaves or new shoots. They live on the surface and send hollow tubes into the plant to suck out nutrients. Some powdery mildews attack a range of plants – some only attack one plant, or at the most, two or three. Powdery mildew is worse in humid weather, and once it has got a hold, it will keep growing, even in dry weather.

Downy mildew is also a group of related fungi, also worse in humid weather. The infected patches appear first UNDER the leaves. Downy mildew grows within a plant and sends out branches through the victim’s stomata (the microscopic openings in the leaves) to create pale patches on the leaves. The problem usually disappears in dry weather, or sometimes if you improve air circulation or stop overhead watering.

Spacing plants to allow good air circulation will help to control some fungal diseases. Environmental problems such as heavy rain, very hot sunshine, strong winds and consistently high night temperatures can also lead to the development of these diseases. The soil should be kept rich in soil organisms to provide conditions that are favourable for the vigorous growth of beneficial fungi and bacteria that will feed on other more destructive types.

 

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3 thoughts on “Understanding Mildews

  1. Pingback: What’stomata with you? | Queensland Begonia Society

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