Powdery mildew is a fungus that looks like light-coloured powder on a plant's leaves. Different powdery mildew fungi attack different plants, but the treatment for these fungi is the same. If powdery mildew is not treated, the plant could eventually die.
Cause and Symptoms
Powdery mildew usually starts with small round, white or greyish powdery spots that quickly expand. Powdery mildew does not like full sun or high heat and appears on plants that are in shade when the temperatures are between 20.0 and 25.0 degrees C, with a relatively high humidity. Symptoms generally appear late in the growing season when the temperatures become cooler and humidity is high. Plants that are close together in shaded areas are particularly susceptible. Powdery mildew injures a plant by depleting nutrients and causing distorted leaves and buds, leaf drop and a decline in the plant's vigour and growth.
At the early stage, spots of powdery mildew may be removed by cleaning the leaves. Large areas require fungicide spray. Many sprays are available, but not all are effective on every plant type. Carefully read the label to make sure the fungicide will work on your particular type of infected plant.
Sulphur-based sprays are the most effective fungicide sprays for powdery mildew. Because these sprays can cause injury to some plants, read the label thoroughly before using. You can make your own sulphur spray by mixing several crushed cloves of garlic with water. As an alternative to sulphur, copper sprays can be quite effective. Whatever spray you use, begin as soon as you notice the problem and continue throughout the remaining growing season.
Because the powdery mildew can survive in unlikely circumstances, it's important to remove all the leaves and debris around infected plants and dispose of it responsibly. Do not add to compost.