Causes and Control Methods of Southern Blight in Phalaenopsis Orchids

Fellow plant lovers probably all know that the flower most prone to disease is the "rose," but even so, many people on the market still like to grow it, because rose blooms have overlapping petals that look beautiful and are very pleasing to the eye when placed at home. In recent years, the market has quietly begun to change, roses have become less popular, and in their place is the "phalaenopsis orchid," for a simple reason: the flower shape is attractive, and it is not very prone to disease.

As more people come to love phalaenopsis orchids and growing environments differ, they will more or less develop some diseases they are not usually prone to (fungal infections). Especially in the south, whenever hot weather hits, it may be followed by torrential rain, and under this alternation of high temperature and high humidity, the stems are prone to rotting, which then leads to infection by pathogens.

Generally speaking, the pathogen that develops under high temperature and humidity is called "southern blight," and the diseased area is on the stem near the root of the plant. The bacteria mainly hide in the flower pot, or in sphagnum moss or bark that has not been thoroughly sterilized, and in some cases the disease is contracted because the water used for watering the flowers is not clean.

Diseased phalaenopsis orchids, from seedlings to adult plants, will all suffer, especially the stem base and roots. When the disease strikes, yellow-brown water-soaked spots grow at the root-stem area, a state somewhat similar to the early symptoms of soft rot, making it hard to distinguish. But later, the lesions grow larger and larger, turning brown and beginning to rot. If recently the ambient humidity has been high, and white thread-like mycelium as well as mouse-dropping-like sclerotia are found growing on the sphagnum moss, then it can mostly be judged as southern blight.

To prevent and control this disease, master these few moves. First, take out the sphagnum moss and sterilize it with steam, and disinfect the flower pot with 0.2% to 0.5% concentration potassium permanganate, or with a 50% carbendazim solution diluted 1500 times. Then, for prevention, when hot and humid weather hits, be sure to ventilate more promptly and let in more light to reduce the surrounding humidity.

Also, the water used for watering should be left to stand overnight before use, so as to let unclean matter in the water settle to the bottom as much as possible. Finally, once a diseased plant is found, clear it away and burn it immediately, and at the same time immediately use medicines such as Bordeaux mixture and mancozeb, diluted in proportion and sprayed once a week for 3 to 5 weeks in a row.