Causes of Black-Brown Spots on Phalaenopsis Leaves and How to Treat Them
Nothing worries a plant lover more than suddenly discovering black-brown spots on their Phalaenopsis leaves! What exactly is going on? And once you find black spots, how do you fix it?
What could these black-brown spots be? The most common cause is disease, such as soft rot and anthracnose. Soft rot is caused by bacteria; the spots feel soft and sticky and give off a foul odor, and if not treated in time, the whole plant will rot away. Anthracnose is caused by fungi; the spots have black-brown edges and grayish-white centers, gradually expanding and merging together, and in severe cases the leaves simply dry up.
Besides disease, pests can also cause spots on the leaves. Small insects like spider mites and thrips hide on the undersides of leaves and suck the sap, leaving dense little black dots, and if you look closely you can also find the webbing or excrement they leave behind. If there are small insects crawling around near the spots, then you can basically be sure it is a pest problem.
It could also be trouble caused by improper care. If you water too often, the sphagnum moss stays wet all the time, the roots cannot breathe properly, and this shows up through the leaves as black-brown spots. If you accidentally splash concentrated fertilizer on the leaves while fertilizing and do not clean it off in time, it will burn the leaves and form spots. If you suddenly move the Phalaenopsis from indoors into blazing sun, or if the temperature is too low in winter and the plant gets frostbitten, black spots will also appear on the leaves.
If you find black spots on your Phalaenopsis leaves, do not hesitate, treat the problem right away! If it is disease, first cut off the diseased leaves, cutting as much healthy tissue as possible to prevent the pathogen from spreading, and remember to disinfect the scissors afterward. Then spray a fungicide, such as carbendazim or thiophanate-methyl, diluted according to the instructions, once a week for 3 - 4 consecutive sprays.
If it is caused by pests, and there are only a few, dip a cotton swab in alcohol and wipe them off. If there are many, go straight to an insecticide, such as imidacloprid or abamectin, also diluted in the proper ratio, spraying mainly the undersides of the leaves and the stem, once every 5 - 7 days until the insects are gone.
If the spots are caused by care problems, you need to adjust your methods right away. Change watering to "water when dry, dry out between waterings" and wait until the surface of the sphagnum moss turns pale before watering. When fertilizing, be careful not to get it on the leaves, and if you accidentally do, rinse it off immediately with clean water. Move the Phalaenopsis to a ventilated spot with bright, indirect light, and keep it warm in winter, never letting the temperature drop below 10°C.
Actually, black spots on a Phalaenopsis are like a person catching a cold or running a fever: if you spot them early and treat them promptly, the plant will soon recover its health. By observing the leaves closely on a regular basis and doing a good job of prevention, with regular ventilation and the right amount of watering and fertilizing, you can keep your Phalaenopsis free of black spots.