Leaves turning brown then yellowing and dying

Question

I have a climber which I think is a ‘Mandevilla ‘out back under shade. It’s turning brown from the middle of the leaf then yellow and completely dying. I was told that they get quite thirsty in summer. Have I over watered or is something wrong with the soil?

Answer 1

Mandevilla can suffer yellowing or browning leaves from a few different causes.
They need partial sunlight for at least 6 hours a day.
Over or underwatering can cause yellowing or dying leaves. Make sure the soil is moist but not soggy.
Insects can cause leaf damage and yellowing leaves, inspect the underside of leaves for signs of insects and treat with a insecticide if needed.

I do believe your plant may be suffering from a leaf spot infection. These often start with a brown or yellowing spot on the leaf, which spreads from leaf to leaf.
This infection can also spread to other plants in your garden.
Prune off any diseased leaves from the plant and remove any that have fallen unto the ground under the plant.
Treating the plant with a fungicide that is made for blooming plants may help but it is possible the disease is bacterial and will not respond to treatment and should be removed from the garden.

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm