The Q&A Archives: White Growth On Bush

Question: I have an evergreen bush with small smooth shiny oval leaves, similar to boxwood but I've been told it is a holly. It has a powdery white substance on the leaves, which is growing or increasing fairly rapidly. What is is and how do I get rid of it?

Answer: Although it's unusual for plants with shiny leaves to become victim, it sounds as though your plant has powdery mildew. Powdery mildew is a fungal disease that attacks plants when environmental conditions are right (warm days, cool nights, some humidity) and air circulation is poor. You can help avoid powdery mildew by giving plants the required exposure to sunshine, and plenty of elbow room so there's good air circulation all around them. Some plants are more resistant to powdery mildew, so choose carefully and avoid those that are mildew-prone.

Unlike most other fungal diseases, powdery mildew can be held in check by strong sprays of water that simulate a downpour.

Another effective treatment is regular sprays with compost tea solution. To make the spray, mix one part mature compost that contains some manure with five parts water. Let the mixture sit in the shade for two weeks, then filter through cheesecloth and spray on your plants. You can dilute it by half if you like. Repeat every two weeks.

I hope you have some success with these methods. Good luck.

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