Orchid leaves develop pinhead-sized spots on the underside; prevent sand spot disease in the hot season

Sand spot disease is caused by fungi of the genus Cercospora. It first produces many pinhead-sized brown or tan sandy spots on the underside of the leaves, which then enlarge to form many irregular spots. The disease only infects old leaves near the base; the central leaves are generally not affected. In severe cases, black spots also appear on the upper surface of the leaves, but there are noticeably fewer black spots than on the underside. Occurrence characteristics: it is more severe under high temperature and high humidity. This disease is not highly contagious and occurs only once a year; after July it no longer infects, and seedlings of the current year are not susceptible.

Control: because sand spot disease occurs in concentrated patches, there is no need to spray fungicide over a large area; simply spraying the few affected leaves is enough. Carbendazim at 1000 times dilution, or chlorothalonil at 1000 times dilution, will both work.