What is causing the yellowing on my trumpet tree leaves?
What's causing the yellowing on my trumpet tree leaves? It gets watered every day by rotating sprinklers. It produces masses of flowers despite it. I pruned it hoping to improve its shape and provide more nutrient flow to leaves, instead of flowers, to prove the color. Still yellowing.
It might just be that those leaves are old - older leaves do turn yellow before falling off.
Is your water brackish (does it have any salt in it)? Brugmansia is not salt-tolerant.
Are you fertilizing? Brugmansia are heavy feeders, and it might be a deficiency. Although I would suspect that all the leaves would look like this, and not just a group.
It could be spider mites. To see if it's mites, do the "tap test." Take a white piece of paper and hold it under a leaf as you tap the leaf - a good thwack to knock the mites onto the paper. They are TINY. You might also be able to see fine webbing on the undersides of the affected leaves. If it's mites, try horticultural oil at first, and a miticide if that doesn't work. Do not use regular insecticides as they have little effect on mites. Collier County Agent Doug Caldwell has an excellent fact sheet on spider mites: http://collier.ifas.ufl.edu/CommHort/CommHortPubs/Southern%20Red%20Mites.pdf