Control Methods for Anthracnose and Leaf Blight in Orchids

OrchidAnthracnose Symptoms: The symptoms of anthracnose vary depending on theorchidvariety, with differences in symptom manifestation. It mainly damages the leaves, initially appearing more on leaf tips and leaf margins. After the lesions at the leaf tip expand, they form entire sections of dead leaves. Lesions on leaf margins are often semicircular or irregular in shape, while lesions in the middle of leaves are round or oval, with lesion sizes of 2-20 mm. Lesions can merge together, forming streaks or causing entire sections of leaves to die. The color of lesions may be reddish-brown in the early stage and dark brown in the later stage, or some become dark brown with the center turning grayish-white. Small black dots develop on the lesions, sometimes arranged in concentric rings. These small black dots are the pathogen's acervuli. Pathogen: COLLETOTRICHUM ORCHIDEORUM Belongs to Deuteromycotina, genus Colletotrichum. Acervuli are flat and circular, with or without setae, arranged peripherally, dark brown, with several septa. Conidia are cylindrical, colorless, single-celled, containing 1-2 oil droplets. Disease cycle: Mycelium overwinters on diseased plants or in diseased debris in soil. Conidia can also overwinter, but with low germination rates. The pathogen begins infecting in early April and stops causing disease by the end of November. The peak occurrence is from April to August. New leaves begin to develop disease in late July, with the peak from late August to September. The pathogen mainly invades through wounds, but can also penetrate through the epidermis. Around 25°C with relative humidity above 85%, conditions are favorable for disease epidemics. The plum rain season and typhoon season are peak periods for disease occurrence. Heavy rain after summer high temperatures also favors disease development.Orchidvarieties show obvious differences in disease severity.Cymbidium goeringii，Cymbidium kanranare more severely affected,Cymbidium faberiis moderately affected. Control Methods 1. Agricultural control: For outdoorcultivation, shade equipment should be properly installed, and the spacing between pots should be well adjusted to ensure both ventilation and light penetration while maintaining a certain level of air humidity. Use decomposed organic fertilizer, avoid alkaline water, water from the edge of the pot to reduce the time leaves stay wet, prevent strong winds, heavy rain and other mechanical damage to reduce opportunities for pathogen invasion, and promptly remove and destroy diseased debris. 2. Chemical control: Commonly used agents include chlorothalonil 75% wettable powder, mancozeb 50% wettable powder, carbendazim 50% at 800 times dilution, thiophanate 70% at 600-800 times dilution, etc. Orchid Leaf Blight Also known as round spot disease, sometimes occurring mixed with anthracnose. After infection, it easily causes leaf blight. Symptoms: The affected areas are mainly on the lower part of leaves. Lesions are initially water-soaked and light brown, later with dark brown margins and the center gradually turning lighter brown. Sometimes a few light-colored concentric rings appear. Light brown small protrusions are scattered on both the front and back of lesions, which are the pathogen's acervuli. After maturing, they break through the epidermis, with the opening being round, boat-shaped or irregular, surrounded by raised epidermis. When moist, they appear as yellowish-brown protrusions. Lesions can interconnect with each other, causing large areas of leaf death. Pathogen: CYLINDROSPORIUM DIOSCREAE Belongs to Deuteromycota, genus Cylindrosporium. Acervuli are discoid, conidiophores are short, filamentous, straight or slightly curved, with rounded ends, colorless, single-celled, with smooth surfaces. Disease cycle: The pathogen overwinters in diseased leaf tissues. It spreads via rainwater. Warm and humid weather favors pathogen spread and invasion. Old leaves begin to develop disease in late April, with the peak from late May to June, and the disease stops developing in November. New leaves are affected more severely than old leaves. Compacted soil, pots placed too close together, poor ventilation and light penetration, and watering with low-temperature water can all aggravate disease occurrence. 1: Prune diseased leaves, improve ventilation and light conditions, and protect from rain in summer. ⟧ 2: During the growing season, use chlorothalonil 70% at 500-600 times dilution, tecloftalam 50% at 800 times dilution, zineb 65% at 500 times dilution, spraying once every 10-12 days. (Kuai Xue Shi Qing)