Can anyone tell me what is going on here (see attached photos)? Yesterday morning I noticed tiny orange spots covering the lower (abaxial) surface of the leaves of a plumeria (frangipani) tree in my yard. At first I thought they were scale insects, but when I looked with a magnifying glass they looked more like sporangia. When I shook the leaf, orange dust came off, looking like spores. I shook some onto a sheet of blue paper and took a photo, but I have no way to magnify them, so they don’t look like much in the attached photo. The sporangia are a little less than one millimeter in diameter. The upper (adaxial) leaf surface has yellowish spots opposite the sporangia, and older leaves appear to be developing necrotic spots. Other than these spots, however, the trees appear healthy. My neighbor’s tree – a different variety of the same species, Plumeria rubra – also has these sporangia. A Plumeria obtusa tree in my yard shows no sign of the sporangia.
From: Monica Gruber <email@example.com>
To: "firstname.lastname@example.org" <email@example.com>, "firstname.lastname@example.org" <email@example.com>
Subject: RE: [pestnet] Fungus on Plumeria Leaf? [4 Attachments]
Could it be Plumeria rust?
There's a fact sheet on this rust in the Pacific Pests & Pathogens app, no. 243.
You can download the app from the Google or Apple 0nline stores. Just type in PestNet.