How to Prevent Black Spots on Orchid Leaves

Orchids have fairly demanding care requirements, and the slightest slip can lead to problems such as black spots on the leaves. For example, if you water from overhead, it is easy to splash potting soil onto the leaves, causing them to scorch. If fertilizer solution gets on the leaves during feeding and is not immediately rinsed off with clean water, black spots and scorching will appear on the leaves. If you do not shade the plants carefully in spring and summer, the intense sun will turn orchid leaves yellow and scorched. In an environment with a lot of coal smoke, orchids develop black spots from the smoke damage. In addition, when orchids are affected by anthracnose, black spots often appear on the leaves.

Orchid anthracnose is especially likely to occur, and sometimes becomes quite severe, during the plum rain season with high temperatures and poor ventilation, or during long spells of autumn rain. Its symptoms are as follows: at first only semicircular or circular brown spots appear on the leaves, which gradually turn dark brown; many of the lesions expand into streaky dark brown patches, and in the later stage the center of the lesion turns grayish white and covered with many tiny black dots. The disease is most often seen on the middle and upper parts of the leaves. When this disease is found, the diseased leaves should be cut off. At the first sign of it, in addition to improving ventilation, you can spray 50% carbendazim wettable powder at a 500-fold dilution, or thiophanate wettable powder at a 500-fold dilution, once a week for 3 to 4 consecutive sprays, which gives fairly good results. To prevent infection by pests and diseases, orchids should not be placed too crowded or too densely together, and the leaves should not be allowed to cross over one another; a well-ventilated environment with good light penetration should be maintained. (Xu Rui)