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How to Identify and Control Anthracnose in Orchids? A Full Analysis of Practical Tips

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Anthracnose occurs in all orchid-growing regions of China. In severe cases, the disease not only affects the normal growth of orchids but also causes entire leaves to wither and die. Besides harming terrestrial orchids (that is, Chinese orchids, or orchids for short) such as Cymbidium goeringii, Cymbidium sinense, Cymbidium faberi, Cymbidium ensifolium and Cymbidium kanran, anthracnose also harms epiphytic orchids such as Cymbidium hookerianum and Cymbidium wilsonii
Anthracnose occurs in all orchid-growing regions of China. In severe cases, the disease not only affects the normal growth of orchids but also causes entire leaves to wither and die. Besides harming terrestrial orchids (that is, Chinese orchids, or orchids for short) such as Cymbidium goeringii, Cymbidium sinense, Cymbidium faberi, Cymbidium ensifolium and Cymbidium kanran, anthracnose also harms epiphytic orchids such as Cymbidium hookerianum and Cymbidium wilsonii, as well as many other flowers such as Dieffenbachia (Dumb Cane), Matthiola (Stock), Calendula officinalis (Pot Marigold), Hibiscus rosa-sinensis (Chinese Hibiscus) and Osmanthus fragrans (Sweet Osmanthus).

I. Symptom characteristics. Anthracnose mainly harms orchid leaves, and sometimes also infects stems and fruits. Leaf spots initially appear round or oval, with a light brown or grayish-white center, dark brown or blackish-brown edges, and a chlorotic halo around them; later, small black dots form on the spots, scattered or arranged in a slightly concentric pattern, and under moist conditions an orange-yellow sticky substance appears. As the disease develops, the leaf spots can expand into irregular large patches several centimeters long, or the spots can join together into continuous areas, ultimately causing the leaves to turn yellow and wither. The leaf spots range in size from 3-20 mm, varying greatly. When stems and fruits are affected, irregular or elongated dark brown spots appear.

II. Disease development patterns. The pathogen overwinters in diseased leaves, diseased leaf debris and withered basal bracts of leaves, and in the following year, under suitable climatic conditions, spreads via wind, rain and insects; it mainly invades plants through various wounds. The disease can occur almost year-round, but is severe in summer and autumn. For example, during the plum rain season in the south, or when typhoons accompanied by heavy rain occur in autumn and injure orchid leaves, or under conditions of high humidity and muggy heat, overcrowded placement, poor ventilation and water accumulation in pots, the disease is most severe at these times. Watering from above the plant (overhead watering) easily spreads the disease. Orchids divided and propagated in the same year often suffer severe disease because their roots are easily damaged. Heavy, compacted potting soil also worsens the disease.III. Control methods1. Strengthen cultivation management: The greenhouse should be ventilated and let in light. In winter and early spring of the following year, special attention should be paid to keeping warm, so as not to subject the plants to freezing or frost damage, thereby enhancing their ability to resist disease. After being moved outdoors, they should be placed in a shade structure to protect them from wind and rain, while the structure should also let in sufficient sunlight; watering is best done by slowly pouring water in from the edge of the pot or by sub-irrigation (soaking the pot), as this can reduce the spread of pathogens splashed by water droplets from overhead watering. Pots should not be placed too close together. Fertilization of orchids should be done scientifically. As is well known, fertilizer for orchids should be well-rotted rather than raw. Applying raw fertilizer very easily triggers anthracnose. For potted plants, the soil should be replaced with fresh soil.2. Remove sources of infection: Promptly remove diseased leaves and their debris; especially before bringing plants indoors in winter, thoroughly remove diseased leaves from the plants and diseased debris from the pots, and burn or bury them deeply, so as to eliminate the sources of infection and prevent the disease from spreading. In winter and spring, spray the ground, pot surfaces and plants thoroughly with 0.5-1% Bordeaux mixture 1-2 times.3. Chemical control: Before the disease occurs, spray with 0.5-1% Bordeaux mixture, or 65% zineb wettable powder at 600-800 times dilution, once every 7-10 days, which provides good protection. During the disease period, spray with 50% carbendazim at 800 times dilution or 75% thiophanate-methyl at 1000 times dilution; both can control the spread of the disease.4. Non-pesticide control methods:(1) Vinegar. Spraying vinegar on orchid leaves can control anthracnose. Mix 1 tablespoon of vinegar into 1 kg of clean water and spray the orchid plants. Vinegar can also be added when using pesticides.(2) Chive juice. Mix chive juice and clean water at a ratio of 1:60, and use it to spray orchid plants, 2 times per day, repeating for several days, which can treat anthracnose.(3) Pig bile. Mix pig bile and clean water at a ratio of 1:100, and add a small amount of laundry detergent; use it to spray orchid plants, which can control anthracnose and soft rot.(4) Quicklime aqueous solution. First use an appropriate amount of water to slake quicklime into powder form, then take the slaked quicklime powder and clean water at a ratio of 1:60, place them in a container to soak, and take the clarified liquid to spray around orchid plants to control anthracnose. Quicklime is alkaline and can also control orchid southern blight.

Identification and Control Tips for Orchid Anthracnose

Anthracnose occurs in all orchid-growing regions of China, with damage being relatively severe especially in Tianjin, Shanghai, Nanjing, Guangzhou, Chengdu, Lianyungang and Xi'an. In severe cases, the disease not only affects the normal growth of orchids but also causes entire leaves to wither and die. Besides harming terrestrial orchids such as Cymbidium goeringii, Cymbidium sinense, Cymbidium faberi, Cymbidium ensifolium and Cymbidium kanran, anthracnose also harms epiphytic orchids such as Cymbidium hookerianum and Cymbidium wilsonii, as well as many other flowers such as Dieffenbachia (Dumb Cane), Matthiola (Stock), Calendula officinalis (Pot Marigold), Hibiscus rosa-sinensis (Chinese Hibiscus) and Osmanthus fragrans (Sweet Osmanthus).

I. Symptom characteristics. Anthracnose mainly harms orchid leaves, and sometimes also infects stems and fruits. Leaf spots initially appear round or oval, with a light brown or grayish-white center, dark brown or blackish-brown edges, and a chlorotic halo around them; later, small black dots form on the spots, scattered or arranged in a slightly concentric pattern, and under moist conditions an orange-yellow sticky substance appears. As the disease develops, the leaf spots can expand into irregular large patches several centimeters long, or the spots can join together into continuous areas, ultimately causing the leaves to turn yellow and wither. The leaf spots range in size from 3-20 mm, varying greatly. When stems and fruits are affected, irregular or elongated dark brown spots appear.

II. Disease development patterns. The disease is caused by infection by several species of Colletotrichum fungi. The pathogen overwinters in diseased leaves, diseased leaf debris and withered basal bracts of leaves, and in the following year, under suitable climatic conditions, spreads via wind, rain and insects; it mainly invades plants through various wounds. The disease can occur almost year-round, but is severe in summer and autumn. For example, during the plum rain season in the south, or when typhoons accompanied by heavy rain occur in autumn and injure orchid leaves, or under conditions of high humidity and muggy heat, overcrowded placement, poor ventilation and water accumulation in pots, the disease is most severe at these times. Watering from above the plant easily spreads the disease. Orchids divided and propagated in the same year often suffer severe disease because their roots are easily damaged. Heavy, compacted potting soil also worsens the disease.

III. Control methods

1. Strengthen cultivation management: The greenhouse should be ventilated and let in light. In winter and early spring of the following year, special attention should be paid to keeping warm, so as not to subject the plants to freezing or frost damage, thereby enhancing their ability to resist disease. After being moved outdoors, they should be placed in a shade structure to protect them from wind and rain, while the structure should also let in sufficient sunlight; watering is best done by slowly pouring water in from the edge of the pot or by sub-irrigation (soaking the pot), as this can reduce the spread of pathogens splashed by water droplets from overhead watering. Pots should not be placed too close together. Fertilization of orchids should be done scientifically. As is well known, fertilizer for orchids should be well-rotted rather than raw. Applying raw fertilizer very easily triggers anthracnose. For potted plants, the soil should be replaced with fresh soil.

2. Remove sources of infection: Promptly remove diseased leaves and their debris; especially before bringing plants indoors in winter, thoroughly remove diseased leaves from the plants and diseased debris from the pots, and burn or bury them deeply, so as to eliminate the sources of infection and prevent the disease from spreading. In winter and spring, spray the ground, pot surfaces and plants thoroughly with 0.5-1% Bordeaux mixture 1-2 times.

3. Chemical control: Before the disease occurs, spray with 0.5-1% Bordeaux mixture, or 65% zineb wettable powder at 600-800 times dilution, once every 7-10 days, which provides good protection. During the disease period, spray with 50% carbendazim at 800 times dilution or 75% thiophanate-methyl at 1000 times dilution; both can control the spread of the disease.

4. Non-pesticide control methods: (1) Vinegar. Spraying vinegar on orchid leaves can control anthracnose. Mix 1 tablespoon of vinegar into 1 kg of clean water and spray the orchid plants. Vinegar can also be added when using pesticides. (2) Chive juice. Mix chive juice and clean water at a ratio of 1:60, and use it to spray orchid plants, 2 times per day, repeating for several days, which can treat anthracnose. (3) Pig bile. Mix pig bile and clean water at a ratio of 1:100, and add a small amount of laundry detergent; use it to spray orchid plants, which can control anthracnose and soft rot. (4) Quicklime aqueous solution. First use an appropriate amount of water to slake quicklime into powder form, then take the slaked quicklime powder and clean water at a ratio of 1:60, place them in a container to soak, and take the clarified liquid to spray around orchid plants to control anthracnose. Quicklime is alkaline and can also control orchid southern blight.

Editor in charge: Molika

Identification and Control of Major Orchid Diseases

I. AnthracnoseAlso known as brown spot disease, it mainly harms orchid leaves. Its symptoms are oval spots appearing on the leaf surface, growing from small to large, turning from yellow to black, and in severe cases rotting in continuous patches. It mostly occurs during the plum rain season, and is most prevalent when humidity is above 80% with high temperature and muggy heat. When discovered, immediately cut off diseased leaves, burn them in a concentrated manner, clean up the surrounding environment, strengthen ventilation, reduce humidity, and then spray with Penkco at 2000-3000 times dilution, or Bijunsha at 800-**** times dilution. Spray once every 10-15 days, for 2-3 consecutive times, which can achieve an inhibitory effect.

II. Soft rotMostly occurs in April-May. As rainwater carrying the pathogen enters the young growing point, water-soaked small spots appear, changing from brownish-yellow to black, until they become foul-smelling and die. When it occurs, promptly move the plant to a ventilated place with less moisture, use medicated cotton to absorb the water from the bud core, and spray with 1% Bordeaux mixture or chlorothalonil at 500 times dilution, once every 10-15 days, for several consecutive sprays.

III. Root rotMostly occurs under high temperature and high humidity. When the potting soil is waterlogged, the soil is compacted, there is high acidity, or fertilizer is applied too strongly, Fusarium takes the opportunity to invade the roots, causing the roots to gradually rot, and the plant dies because it cannot absorb nutrients. If discovered early, promptly repot, discard all the growing medium, cut off rotten roots and withered leaves, soak the entire orchid plant in a 0.1% potassium permanganate solution for about 15 minutes, take it out, wash it clean and let it dry, then use "Speed Rooting" 2 g diluted in 40-60 kg of water, soak the orchid plant thoroughly for 60 minutes, then let it dry, replant it in renewed growing medium, and place it in a ventilated spot.

IV. Southern blightDuring hot and humid seasons, the mycelium of the pathogen first invades from the pseudobulb or base, and then harms the roots. After the disease occurs, the leaves gradually turn yellow and dry out from bottom to top, and white silky mycelial strands wrap around the surface, slowly spreading to the whole plant. In any orchid root infected by this disease, the center becomes hollow, leaving only fibrous tissue, showing a dry death phenomenon of broken leaves and broken roots. To prevent the occurrence of southern blight, before planting, choose clean and sterilized growing medium, and do not apply overly concentrated organic fertilizer. Soak the diseased plant in chlorothalonil at 600 times dilution for 20 minutes, then wash it clean with water and let it dry, then use "Speed Rooting" 2 g diluted in 40-60 kg of water, soak the orchid plant thoroughly for 60 minutes, then let it dry, replant it, and place it separately in another place, isolated from normal orchids that have not developed the disease, to prevent transmission.

V. SunscaldIn places lacking shade, when orchids are exposed to strong summer sunlight, some of the chlorophyll in the leaf mesophyll is damaged by the exposure and dies, and then the pathogen invades and causes pathological changes; the symptoms are mostly brown or black spots. Control methods focus on strengthening shade facilities, especially preventing exposure to intense midday sunlight.

VI. Orchid leaves turning yellow or leaf tips drying outThese are not necessarily caused by pathogens; most are physiological phenomena resulting from poor cultivation management. Attention should therefore be paid to solving them by improving water and fertilizer conditions, regulating ambient temperature and humidity, and frequently ventilating and exchanging air.

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