Ha una macchia fogliare di origine probabilmente batterica, almeno tale è la manifestazione sintomatologica che provoca
Acidovorax (=Pseudomonas) cattleyae su phalenopsis. Ecco un paio di consigli di cosa fare (altre indicazioni potrai trovare in rete digitando il nome del patogeno che ti ho surriportato):
Yellow Leaf Spots
1)
If your plant’s leaves develop yellow leaf spots with brown centers, like this image, then your plant is infected with a bacteria called pseudomona. We recommend that you cut the leaf, in half, with disinfected scissors 2 inches beneath the infected spot. This may stop the spread of the pseudomona. We do not recommend using any chemical to cure the plant as pseudomona is very difficult to cure. Be sure to keep your orchid in sanitary conditions and try not to handle your orchid frequently to help prevention.
2)
Treatment: Immediately remove infected tissue using a sterile instrument, spray bactericides containing quaternary ammonium products like Physan or copper compounds on infected and adjacent plants following label instructions (copper should not be used on dendrobiums or blooming plants), or apply the home remedy of hydrogen peroxide. Disinfect growing area with 10% bleach solution. Treat nearby plants as well as those that are diseased.
Prevention: Pseudomonas cattleya is a water-borne pathogen that prefers warm, moist conditions. Reduce humidity and temperature (if possible), eliminate overhead watering and increase air circulation.