Vanda fungus issue
 

Good afternoon, I have a serious problem with some of my Vandas. They have been attacked by some fungus (they look like Cercosporoids or something similar), with black spots and dots, some of which become necrotic. In addition, the leaves have a very dark colour (but the roots seem to be in good condition). I have treated them with Banrot a couple of times, but they do not seem to improve. I grow them under LED lights, in an environment with high humidity (70-90) and temperatures of 15-16 ºC at night and 22 ºC during the day. In summer they go outside. The photo corresponds to Vanda Roberts Delight Black. I would really appreciate some help because I don't know what I can do. Thank you very much!!!

I agree, your plant has fungus that has been called Cercospora, Guignardia, Phyllosticta and Septoria. A systemic fungicide that kills the organism is needed. Banrot is not effective against these organisms.

Banrot is also not approved for home gardeners in the US, only for commercial users, because it is so toxic:
https://www3.epa.gov/pesticides/chem...0-20210422.pdf

Have a look at the Diseases/Leaf Spot section of the St Augustine Orchid Society for recommendations:
https://staugorchidsociety.org

This publication shows recommendations for antifungals to use on various ornamental plants. It does not list any leaf spot products for orchids, but if you search the document on the term Phyllosticta you will find antifungals recommended for other plants:
https://njaes.rutgers.edu/pubs/ornam...36section1.pdf

I would like to reiterate that people should not use fungicides unless they know the fungicide to be used is effective against the fungus infecting the plant. Not all fungicides treat all fungi species. Not all fungi species will be killed with any one fungicide. Using fungicides blindly risks exposure to highly toxic chemicals that may be ineffective for the fungus present.

Thank you very much for the information and your warnings, Estacion Seca. I just thought that Banrot was effective for this type of fungus. I bought it years ago from the USA. Here in Europe, it is difficult to find some of the fungicides commonly used for leaf spots (Daconil, Cleary's 3336, Pageant, Heritage are recommended at St. Augustine Orchid Society - North Florida Orchid Growing), and I have no references as to what their equivalents are here. Perhaps some European grower can help me. Thank you very much again.