The Q&A Archives: White Powdery Substance on Mandavilla

Question: My sister has a beautiful Mandavilla trumpet vine. We've noticed a white powdery substance on the stem and under the leaves. We washed it off but it reappeared. Any ideas as to what it might be and how to treat it? Also, what would be the proper careand feeding for this type of plant?

Answer: Sounds as though your mandavilla has powdery mildew, a fungus that attacks plants and spreads rapidly. The mildew will cause the leaves to wilt and turn brown. To control, pick off the infected plant parts and dispose of them (this will help stop the spread and also open the plant up to better air circulation).<br><br>I expect this is an indoor or greenhouse plant and that it will retain its leaves all year. You can also try using a homemade baking soda spray--mix 1 teaspoon <br>baking soda per quart of water; add 1/4 tsp mild soap to help it stick to the leaves. Apply this once a week, and hose down plants between sprayings. <br><br>The plant likes bright light and warm temperatures (minimum of 55F in the winter). It doesn't like a lot of water in the winter and likes to be misted when there are flower buds on the stems. Other than that, prune it lightly to encourage more growth.

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