My Phalaenopsis Orchid has spots on underside of leaves ... Fungus?

Asked November 28, 2018, 4:32 PM EST


I purchased this orchid a year ago from a reputable grower (Fantasy Orchids in Louisville, CO).

This orchid has done extremely well in my house. It has rebloomed once already, and grew more leaves and roots this past summer. Currently it has two flower spikes, each about 3 inches long.
As you can see from the attached photos, it has spots on the underside of one of its lower leaves.

I have removed two leaves already and swabbed the cut/torn edges with isopropyl alcohol. I also moved this plant 5 feet away from the other orchids. I saw spots on a third leaf (same plant), but did not remove it.

The spots have not increased in the past 7 days. No similar spots have appeared on my other orchids.

Should I treat my plants with any substances that would kill the fungus or prevent more fungus from developing? Whatever I use must be safe for cats. They are very curious and have adventurous palates.
Any advice you can give would be much appreciated. If I need to apply fungicide or other remedies, can you tell me where to buy them?

Thank you for your help.

Denver County Colorado

1 Response

Your orchid problem is possibly Black Rot. It can be caused by several pathogens.Initially small black lesions appear near the roots and basal portions of the plant. As the lesions age, they enlarge and could kill the plant. Water is required to spread the spores. You are wise to isolate the plant, reduce period s of prolonged wetness, and provide adequate ventilation. For information on fungicides, refer to Homeowners Guide to Fungicides for Lawn and Landscape disease Management.