Q.yellow fungus growing on mandevilla
What is the yellow fungus growing on the vines of my mandevilla plant? I moved the plant indoors. It is in a pot (8″x 8″). The fungus consists of small yellow spots, slightly raised that are easily rinsed off (I know this because I rinsed the plant off when I brought it in the house). It is on a table in the front bow window that gets direct sunlight until noon. It has always been potted and when I originally rinsed it, the fungus was on only a few vines but now covers them all. At night the house temp never goes below 60 and goes up to 75 during the day. We have a wood pellet stove we heat with and the electric heat is always set at 60 for nighttime. The table with the plant sits in front of the electric baseboard heater.
It sounds like your plant has a Rust Fungus. This can be due to damp growing conditions and poor air circulation.
Neem Oil can be used to treat this fungus.
Your Mandevilla plant can be overwintered with some care.
Here is a link that will help you.