Leaf spot disease on orchids is mainly caused by fungi, the initial signs are usually very small yellow spots or hearts, then spread on the leaves. The cause is often because the orchid garden is not bright enough and the air is imprisoned without ventilation.
It can be caused by 1 of 4 or more of the following fungi:
1. Cercospora fungus symptoms: Infection is initially as a yellow spot on the underside of the leaf. Immediately after superinfection occurs, yellow-green areas may be noted on the upper surface of leaves. These spots will spread around without a fixed shape, it will be slightly sunken and necrotic and then turn purple-brown to purple-black. The points continue to expand radiating around in a circle or in some direction and can eventually cover the entire leaf. The forward range is still yellow. Many infected leaves often fall prematurely, especially if the fungal infection begins near the base of the leaf.
2. Guignardia Mushroom Symptoms: The first signs of guignardia infection are very small, dark purple, long-lasting lesions on both sides of the leaves. These lesions run parallel to the leaf veins and extend into purple streaks or rhombic areas. Spots often combine to form large abnormal lesions that can affect a large portion of the leaf. After time, the lesion centers disappear, the lesions grow, and the lesions feel like sandpaper to the touch. Affects most of the single orchid varieties when the orchid does not have enough light.
3. Phyllosticta Mushroom Symptoms: Phyllosticta spotting can begin anywhere on leaves or pseudobulbs. The lesions are very small, yellow and slightly concave. As it enlarges, it becomes rounder oval and more concave, especially if the infection is on the leaves. Over time, the lesions will gradually turn dark brown or red to purple-black margins. Finally, to black. Severely infected leaves may drop prematurely. The presence of disease may indicate that your orchid is not getting enough light.
4. Septoria Mushroom Symptoms: Small spots may begin on the leaf sides as sunken, yellow lesions. It continues to expand, becoming dark brown to black, round, or irregular lesions. Spots may merge to form large, irregular patches on leaves. Many infected leaves will drop prematurely.
Prevention: Ventilate the truss to allow air movement. Avoid standing water on leaves. Spray preventive medicine monthly. Hanging in the East-West direction helps the orchid to receive enough light and sunshine.
Special medication:
Topsin M (active ingredient Thiophanate-Methyl)
Or Daconil 75WP or Daconil 500SC (Active ingredient Chlorothalonil).
Should be mixed with drugs with active ingredients Carbendazim to treat the disease more thoroughly and make the spectrum of disease prevention and control wider.
