Over night plumeria got black spot just like roses - no rain. I sprayed it with water and joy soap after the sun was not on it (p.m.). It had mild spider mites. At same time, a 6 ft firebush next to plumeria got small spots. I guess a fungus. Will Bayer 3 in 1 knock it out? It's systemic fungicide and food. Ideas on cause?? Thanks for your time.
Black Spot on Plumeria
Certified GKH Gardening Expert
Certainly sounds like a fungal issue. In your area it likely gets pretty hot and humid, which is favorable to fungal growth, especially if plants are grown close to one another. I recommend cleaning any fallen foliage away from the base of the plants and prune a bit to allow for good air movement. Keeping the ground surface clean and a bit dry will go a long way to clearing up black spot problems. You can also spray the plants and ground around them with Mancozeb, which works great on black spot. Neem oil is another effective treatment for black spot problems.