Mandevilla dropping leaves

Question

Purchased pink hardy mandevilla plant about 6 weeks ago, two plants in 1 gallon containers. Transplanted to larger 5 gal pots with mix of sandy potting soil. Both plants have done very well, full of blooms. Plenty of rain, however, and pots seem to drain weak. Suddenly, one of the plant’s leaves started curling and turning yellow and drooping. The other plant has a few curled leaves, no yellow leaves. Have not observed pests. Any clues?

Answer 1

This article discusses yellow leaf curl in mandevillas:
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/yellow-leaves-on-mandevilla.htm