Is this rust fungus on leaves of my Pahphiopedilum Harrisianum

[floempie01]

My Paph seems to be healthy and the leaves have grown over the last half year. But the oldest leave has had yellow spots which seem to develop over time. Is this rust fungus? Should I treat with fungicide, or can I leave it alone?

[estación seca]

What are your ambient temperatures and humidity? Are you growing it in a home, or a greenhouse?

[floempie01]

I have it in the kitchen, about 2m from south window. I don't control the humidity there, soit varies with the humidity in the house. I live in the Netherlands.

[estación seca]

It may be an older leaf dropping naturally. The rest of the plant looks healthy. If it does not spread to other leaves I would not worry. Rust would rarely or never be seen inside a home in North America but I don't know about Europe.

Do you know when it was last repotted? Most Paphs should be repotted every 1-2 years because the medium breaks down rapidly from being constantly moist.