Its leaves seem to be infested with some kind of pest.

Check to see if any can be seen, or take some leaves to a nursery for requesting their opinion and suggestion on what treatment to use.

Also slip the rootball out of the pot and check the condition of the roots. If you see any dark brown roots, that could indicate the plant is being over watered. or the that the soil in the pot does not drain well enough.

Healthy roots that are not dirty from from soil, are usually white.

Rotting roots are medium to dark brown no matter how well you clean the soil away.

Looks like root rot to me too. Most Mandevillas don't like overwatering. I keep mine in small pots or clay pots. making sure that the soil dries out a bit in between watering. They are prone to pests like mealy bugs, white flies and mites besides some deseases like black spot on the leaves and root rot. It would help a lot too if you can have a spraying schedule of fungicide and insecticide/miticide.

Although all three plants received the same care, plants just like humans are still different from each other. Some are weak, some are strong. Hope this helps!

I was actually afraid this plant was dying from UNDER watering....because I have not deep watered for a few weeks! and they have gotten a scattering of rain over that time.

I'll take a look at the roots and see what I see....thanks for the tips.

Hi Rjinga! How are your mandevillas doing? Did you get to check the roots? I hope you found what's caused that problem. If it was underwatering, the young leaves would first wilt and not turn that color as in your pic. I water well with fertilized water (1/2 dose) then let it dry. As I said, I keep mine in small pots, 6" plastic or clay pots that way, they do not stay wet too long. here's a pic of my Mandevillas with my little garden helpers.

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Hi, living in Tenerife, Spain where the temp is allways high I have been growing Madevilla for the past year with no problems. Now one looks unhealthy, the leafs are green but the flower buds don't flower fully. Any idea if it could be over watering ? Another has its leafs turning brown. I am thinking of repotting both of these to see if it helps. What do you think ?

Hello, I am a beginning gardener with a Mandevilla from Home Depot. It bloomed beautiful within the first few days, but now a couple weeks later the bottom leaves are wilting.

I purchased a meter that would tell me the amount of moisture in the soil, the pH, and the amount of light it gets. The pH is good, about 7, but the soil was too wet. I think I used too much builder's sand and not enough regular soil, and so it wasn't draining well. When I dug it out, it was wet and muddy!!!! ): I've just repotted with 3/4 miracle gro soil and 1/4 builder's sand. It's a clay pot with a big ol' drainage hole in the bottom.

What should I do to allow it to recover? I live in Arizona, in zone 9, and I'm worried that the afternoon sun exposure it receives will be too intense while I am trying to get it to recover. I have it on my back porch, which is I guess "partial sun" from 8-2pm and then full sun from 2pm-sunset.

Also, what's an appropriate watering schedule while I'm trying to mitigate the damage I've already done? I know I shouldn't let the soil get completely dry, ever, but I don't want to keep watering the poor guy if he's already drowning.

Thanks for any responses!!!!! My little plant buddy will surely thank you.