Anthracnose of Orchid (1)

Orchid [Cymbidiumspp. Orchid]

[symptoms] the disease spots on the leaves are semicircular, round, oval, fusiform and even irregular in size, some of which are connected to each other into large patches or form dead lines from the leaf tip down. The disease spot is brown, or the middle part is gray or gray-white, and some disease spots are surrounded by a yellowish green halo. In the later stage, there are small black spots with large needles (pathogen conidial disk) on the disease spot, which eventually leads to the withering and yellow of the diseased leaves.

[pathogen and pathogenic characteristics] the pathogen is a semi-known fungus, Colletotrichum gloeosporioides [Colletotrichumgloeos-porioidesPenz.=C.orchidearumAllesch=C.orchidearumAlleschf.cymbidiiAllesch]. The pathogen overwintered with mycelium and conidium on the diseased remains in the diseased leaves or fallen soil. In Guangzhou area, the overwintering period is not obvious, and the infection can begin when the temperature and temperature are suitable in early spring, but it is prevalent in the plum rain season in May and June or in the years with more autumn rain or more Taiwan wind and rain in September and October. The disease can be aggravated by high humidity and muggy weather, especially sunny and rainy weather, or poor permeability of garden, poor management of fertilizer and water, staggered abrasion of leaves, or freezing injury of plants. There were differences in resistance between species and varieties. The iron stem of Cymbidium and Jian Cymbidium were more resistant, while those of Cymbidium, Cymbidium, Han Cymbidium and Jian Orchid were more susceptible.

[control methods] ① cut off the diseased leaves (in the shape of "A") in winter and spring, and collected the disease residues and burned them, then 0.5% Bordeaux solution was sprayed on the ground and plants for 1 or 2 times. ② spray regularly to protect newly extracted leaves [besides referring to chrysanthemum anthracnose, you can also spray 1% Bordeaux solution, 75% chlorothalonil + 70% thiophanil (1:1), 80% anthrax Fumei 600x, 50% benzoate wettable powder 800x, or try 20% tricyclazole 800x]. ③ strengthens the fertilizer and water management and improves the ventilation and light transmission of the garden.