The Q&A Archives: Dropping Leaves On Mandevilla

Question: I recently brought in a mandevilla into my greenhouse. Several days after bringing it in the leaves are turning spotted brown and dropping off starting at the base, I sprayed the plant twice with Ivory soap and water before bringing it in and put insecticidal spikes in the soil. Could this problem be caused by using too strong a soap solution? I have rinsed the leaves several times now.

Answer: In general, these plants are sensitive to being moved and may drop foliage as a result of the change in environment. They do best in a location with bright light and good air circulation, in a location with poor air circulation you may see some fungal problems developing. As the season cools and days are shorter it may defoliate in response to that as well. As it slows down, reduce watering proportionately and stop fertilizing until next spring when it starts to try to grow again. In the meantime, pick up and remove any fallen or discolored leaves. You may also trim it back if desired. In my experience, the plant is more likely to be attracting whitefly than any other pest and this would be treated satisfactorily by washing the plant in a strong spray from the hose prior to bringing it indoors and then possibly with a commercially formulated insecticidal soap -- if needed -- and following the label instructions. I am not sure why you felt the spikes were needed, unless recommended by an extension agent or similar authority to treat a specific pest, I would suggest removing them. Good luck with your mandevilla!

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