Mandevilla yellowing and dropping leaves and all flowers - Knowledgebase Question

Hubertus, WI
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Question by nokian
September 14, 2005
I have a few Mandevilla plants; Alice du pont and they have been growing wonderfully all summer outdoors in containers. All of a sudden a white one started dropping flowers and then leaves were turning yellow and limp like. Not firm and leathery, glossy like when it was happy. It died in 2 weeks. Another pink one lost all flowers in a couple days and leaves are doing the same thing. No traces of insects. Others are doing wonderfully; all in same location & conditions. Just started to give a geneal plant fertilizer because the garden center was out of the others. I don't want to loose this one.
What can be done; or what may I have done wrong. Have over a dozen other Red Riding Hoods and a few of the yellow mandevillas and they are all doing great.

Answer from NGA
September 14, 2005
Unfortunately, based on your description I am not certain what is happening. If the yellowing and wilting coincided with applying the fertilizer then I would suspect an overdose of that. If it was a foliar application you could try rinsing off the leaves; if it was a granular application you can try to scrape it off the soil surface or you might try leaching it out of the soil by watering heavily and letting it drain, repeat several times in quick succession. Too, you would not want to be fertilizing much this late in the season as they need to begin slowing down in preparation for being brought indoors.

Another possibility since the symptoms were sudden, is that something affected the tuber beneath the soil and damaged it or caused it to rot. You might dig down carefully and take a look. Sometimes a bacterial or fungal infection can do this, and also make sure that the drain holes in the ottom of the container are functioning -- overwatering can cause damage signaled by yellowing and wilting.

I am not sure how your nighttime temperatures have been but if the yellowing plants are in a more exposed location and you have suddenly had nights under 50 degrees, it may be related to cold exposure.

Since I am only able to make guesses from a distance, and you have a lot of these plants, I would strongly suggest you work with your county extension to try to identify the cause. Once you know that, you can determine how to proceed. I hope it is nothing too serious.

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