Q.My trumpet tree leaves are turning yellow and curling into themselves. SOS
What should I use?

Certified GKH Gardening Expert
My research shows that pests and diseases are not a serious concern with trumpet tree. However, verticillium wilt is a soil borne disease that can cause yellowing and leaf curling. Anthracnose is a fungal disease that can cause brown spots and leaf curl. I would suggest calling your local university extension service to determine an accurate diagnosis to get the correct treatment.
https://www.gardeningknowhow.com/ornamental/trees/tabebuia-trumpet-tree/tabebuia-tree-care.htm
https://edis.ifas.ufl.edu/st614
https://www.gardeningknowhow.com/extension-search