Question
I have a thriving Gardenia plant indoors which has done well for several years.  Within the last couple of months I have noticed white powdery stuff at the tip of the branches and on top of some of the leaves.  Any suggestions?

Answer
Hi Patricia,

If your description is accurate, then powdery mildew is the problem. (If the white stuff looks like tiny bits of cotton, then it is mealybug and will require a different treatment.)

Powdery mildew appears as irregularly shaped patches of white on the leaf and stem surfaces of some plants. This fungus wipes off leaves, but brownish leaf spots often are left behind. Powdery mildew often attacks tender new growth and destroys it. Once established on a plant, powdery mildew is hard to eradicate because the microscopic spores float invisibly through the air and onto other areas of the plant.

The first step in treating powdery mildew is the cut off the infected tissue, usually the entire leaf or stem. Next you can try spraying all leaf surfaces and stem surfaces and also the surface of the soil with a solution of 1 tsp. baking soda to a quart of water. The sulfur in garlic is also effective, so you can spray with a solution of garlic and water. Safer's makes a non-toxic sulfur spray for mildew. It is reasonably effective but will leave a strong sulfur odor on your hands, so use rubber gloves. Neem oil and horticultural oil sprays are also effective treatments for powdery mildew.  Repeat the spray treatments again in about a week.

NOTE: Be sure to test any of these sprays on a single leaf before spraying the entire plant to be sure that it does not damage the plant

Powdery mildew thrives in locations that are warm, humid and lacking good air circulation. Installing a fan nearby can help deter powdery mildew.

Please let me know if any of this is unclear or if you have any additional questions. If you would like to e-mail some photos to my address below, I may be able to provide some additional insights.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

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