We live in Hawaii and have planted gardenias. Some of them are planted in full sun and are doing very well. Others receive morning sun and are growing well, but the leaves are covered with a dark sticky substance (looks like a mold). There is no sign of white flies. All the plants are on a drip system. Any idea what the mold might be and/or how to prevent? I am considering hand-cleaning with a 30% Simple Green solution.
Certified GKH Gardening Expert
It sounds like sooty mold. This article will help you: https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
I like neem oil. It gets rid of both the fungus and the pests that cause the fungus. Here is more info on neem oil: