Symptoms and Control Methods of Fly-Speck Disease in Orchids

This disease causesorchidsvery little harm, and is generally easily overlooked. It also affects few species, having been found only on Cattleya, Dendrobium and Vanda. Generally speaking, orchids growing in shaded and sheltered spotsorchidsare prone to infection. When the disease occurs, small black spots the size of a needle head and similar in size and color to fly droppings can be seen on both sides of the leaf, composed of tightly interwoven fungal mycelium; they appear on both the upper and lower surfaces of the leaf, but are more common on the underside. These small spots often cluster together, appearing on the leaf as multiple black mounds, and in severe cases, multiple black mounds can cover the entire leaf. The individual black mounds are not independent of one another, but are connected by extremely fine mycelial strands. This fungus does not penetrate the leaf, and it can be wiped off the leaf with a gentle rub. The pathogen of this disease has been identified as Microthyriella rubi. Its control is not a major problem; it can be gently wiped off with a soft cloth strip dipped in water, and conventional fungicides used to control other serious diseases can also control this pest. (Liu Zhongjian)