What to Do When an Orchid Gets Southern Blight? Symptoms and Control Methods Explained
Orchid southern blight is one of the main diseases of orchids, also known as white silk disease, sclerotium disease, etc. Its damage is second only to anthracnose, but once it occurs, the harm and losses it causes will far exceed those of anthracnose. It usually begins infecting in April to May, with the peak incidence from June to August. The disease develops rapidly, causing the affected orchid plants to rot, wither and die. Let's take a look together at the control methods for orchid southern blight!
Symptoms
Southern blight starts from the stem near the ground of the orchid plant, initially appearing as yellow to light brown oozing lesions, then turning brown to dark brown and rotting, and spreading across the soil surface around the roots and the base of the stem, destroying the stem and infecting young leaves and roots, with white mycelium produced on the leaf sheaths and root mass. The affected parts become water-soaked, rot and soften, turn black, until the leaves wither; the pathogen spreads to the pseudobulbs, and the sclerotia change from white to reddish brown to tea brown and become necrotic. In severe cases, the entire leaf cluster of the whole plant withers and dies.
Disease Characteristics
The pathogen of orchid southern blight is a fungus of the Deuteromycotina, and the pathogen overwinters as sclerotia in soil, in fertilizer, and on undecomposed residues. In regions with higher winter temperatures, the mycelium can also overwinter on undecomposed residues. The sclerotia germinate the following year, spread through the soil, and invade and cause damage from the base of the orchid leaves. The sclerotia have strong resistance to adverse environments and can survive in soil for several years, spreading through flowing water, irrigation water, rain splashes and fertilization. The disease is most severe in acidic soil, and hot, humid weather easily induces the disease. Infection begins in April to May, with the peak incidence from June to August. The disease develops rapidly, causing the affected orchid plants to rot, wither and die.
Control Methods
1. Orchid southern blight is prone to occur when the substrate is acidic (pH value less than 5.3), so mixing plant ash at a volume ratio of 1/10 into the substrate, or watering with 0.3% lime water to raise the pH value to around 6.5, can reduce the occurrence of southern blight, with obvious results.
2. Disinfect orchid substrate soil with 0.2% quintozene 500-fold solution or 50% carbendazim wettable powder 600-fold solution. You can also spray the root zone and soil with quintozene 500-fold solution or 70% thiophanate-methyl wettable powder 800-fold solution, or mix 50 grams of quintozene powder with 4 to 5 kg of semi-dry and semi-moist fine sandy soil and scatter it at the root and stem area of diseased plants, which can inhibit the spread and transmission of the disease.
3. In the rainy season from May to June in the south, soil humidity is relatively high, and southern blight is prone to occur on the pot surface. The plants should be quickly moved out of the orchid growing area for “isolation”, and the substrate should be pulled apart, the substrate contaminated with mycelium removed, and the diseased roots cut off. Spray with potassium permanganate solution 1000-fold for disinfection. You can also spray the root system and wounds with 70% thiophanate-methyl 1500-fold solution, and scatter fresh plant ash around the orchid roots, then cover with substrate to protect the roots. Water only after 2 to 3 days; if the substrate is wet, watering can be postponed for another 5 to 7 days. The control effect is good.
4. When orchid southern blight occurs, use medical chloramphenicol injection diluted 2000-fold in water and drench the diseased plants, once a day, for 3 consecutive applications. Once the disease occurs, the diseased leaves should be cut off, ventilation conditions improved, and the whole orchid plant soaked in 10% copper sulfate solution for disinfection. Nearby orchid plants should also be thoroughly sprayed, wetting the base and pot surface, spraying once a day for 2 consecutive applications, which can control the disease with good results.
5. After new orchid shoots grow out of the soil surface, spray with 0.05% chloramphenicol once a week for 2 to 3 consecutive sprays. If the potting soil is dry, this medicine can be applied as a drench to prevent bacterial infection. You can also water or spray with aspirin 1500-fold solution, which can enhance the immunity of orchid plants and prevent the invasion and spread of pathogens.
6. During the new shoot elongation stage and leaf expansion stage of orchids, you can choose medical penicillin, streptomycin, chloramphenicol, or a penicillin mixture diluted to 2000-fold solution, drench the diseased plants, and spray comprehensively, once every 3 to 4 days for 2 consecutive sprays. The control effect is good.
7. After orchids develop the disease, spray with 50% benlate wettable powder 1000-fold, or 50% carbendazim wettable powder 500-fold, or 50% thiophanate wettable powder 500-fold solution, or 70% chlorothalonil wettable powder 800-fold solution, once every 7 to 10 days for 2 to 3 consecutive sprays. The control effect is good.
8. After orchids develop the disease, spraying for control can be done before and after overcast or rainy weather. You can use 50% procymidone powder 500-fold, or 50% vinclozolin powder 500-fold solution, dufulin 500 to 600-fold solution, or 5% validamycin aqueous solution 300-fold, spraying the stems, leaves and pot surface. The control effect is significant.
Symptoms and Control Methods of Orchid Southern Blight
Orchid (scientific name: Cymbidium ssp.): epiphytic or terrestrial herb, with several to many leaves, usually borne at the base or lower nodes of the pseudobulb, two-ranked, strap-shaped or rarely oblanceolate to narrowly elliptic, generally with a broad sheath at the base that surrounds the pseudobulb, and with a joint. The raceme has several to many flowers, with colors including white, pure white, white-green, yellow-green, pale yellow, pale yellow-brown, yellow, red, cyan, and purple. Southern blight is one of the most common plant diseases, with more than 500 host species in as many as 100 families; for example, plants of Cucurbitaceae and Caryophyllaceae often suffer from this disease. Although southern blight is not as common in orchids as gray mold and anthracnose, it is still one of the more common diseases of orchids and is a worldwide disease. Among Chinese orchids, Cymbidium goeringii, Cymbidium sinense and Cymbidium ensifolium, and among foreign orchids, Oncidium, Phalaenopsis, Vanda, Cymbidium hybridum, Dendrobium and Phaius, can all be infected by this disease, often causing certain losses. Here, taking Oncidium as an example, the causes of the disease and control methods are explained.Symptoms:
If conditions are suitable, this disease can infect any part, such as roots, corms, leaves, etc. The diseased parts are often water-soaked and sometimes accompanied by yellow liquid exudation. White silky material grows on the affected parts, sometimes in a radial pattern, and sclerotia the size of rapeseeds are produced on the mycelium, initially white and later brown, with a diameter of 2 mm to 4 mm. When the pseudobulb is infected, the plant eventually collapses and dies.
Disease Conditions:
Sclerotia are the surviving tissue of the pathogen and an important source of infection. They have no dormant period and have strong resistance to adverse environments. The pathogen overwinters as mature sclerotia in diseased parts or enters the soil with diseased residues, and in warm regions it can overwinter as mycelium on organic matter. It can spread with watering and is prone to occur under high temperature and high humidity conditions. Generally, sclerotia begin to germinate mostly in May to June when the temperature reaches 25°C to 35°C and the humidity reaches above 90%, and spread in the soil. The main factors affecting germination are temperature and humidity. The lower limit for pathogen development is 8°C, the upper limit is 40°C, the optimum is 25°C to 33°C, and the optimum pH value is 5.9. Sclerotia can survive for 10 years under indoor conditions, 5 to 6 years under natural conditions, and only 3 to 4 months in water. In the plum rain season in southern China, high temperature, high humidity, plus overly wet substrate and poor ventilation easily lead to the occurrence of this disease.
Control Methods:
Physical Control:
1. During the rainy season, prevent the substrate from becoming too wet and the air humidity from becoming too high, and pay attention to ventilation. Follow the principle of “do not water until dry, and water thoroughly when watering.”
2. Cultivation substrate and flower pots can be treated at high temperature before use. Sclerotia can be killed when the temperature reaches 100°C, and mycelium dies very easily when exposed to the scorching sun.
3. When diseased plants are found, isolate them immediately; in severe cases, destroy them immediately. Clean up diseased plants, diseased leaves, cultivation substrate, etc., to block the source of infection.
Chemical Control:
1. For lightly diseased plants, repot immediately, remove the diseased plants, and soak the orchid plants from the same pot in 1% copper sulfate solution for disinfection. Also spray nearby plants for control. For chemical control, validamycin 500 to 700-fold solution can be used and sprayed directly on diseased plants 2 to 3 times, which can basically completely eliminate the disease. Validamycin is currently one of the most effective agents for controlling southern blight. You can also use 15% triadimefon wettable powder mixed with 100 to 200 parts fine dry soil and scatter it at the root and stem area of diseased plants.
2. Before use, in addition to high-temperature disinfection, the substrate can also be treated with chemicals. For chemicals, 40% quintozene powder can be used. Mix 0.2 to 0.3% of the substrate weight of the chemical into the substrate, or dilute it with water 500-fold and pour it onto the substrate.
Control Methods for Orchid Southern Blight
Orchid southern blight is one of the main diseases of orchids, also known as white silk disease, sclerotium disease, etc. Its damage is second only to anthracnose, but once it occurs, the harm and losses it causes will far exceed those of anthracnose. It usually begins infecting in April to May, with the peak incidence from June to August. The disease develops rapidly, causing the affected orchid plants to rot, wither and die. Let's take a look together at the control methods for orchid southern blight!
Symptoms
Southern blight starts from the stem near the ground of the orchid plant, initially appearing as yellow to light brown oozing lesions, then turning brown to dark brown and rotting, and spreading across the soil surface around the roots and the base of the stem, destroying the stem and infecting young leaves and roots, with white mycelium produced on the leaf sheaths and root mass. The affected parts become water-soaked, rot and soften, turn black, until the leaves wither; the pathogen spreads to the pseudobulbs, and the sclerotia change from white to reddish brown to tea brown and become necrotic. In severe cases, the entire leaf cluster of the whole plant withers and dies.
Disease Characteristics
The pathogen of orchid southern blight is a fungus of the Deuteromycotina, and the pathogen overwinters as sclerotia in soil, in fertilizer, and on undecomposed residues. In regions with higher winter temperatures, the mycelium can also overwinter on undecomposed residues. The sclerotia germinate the following year, spread through the soil, and invade and cause damage from the base of the orchid leaves. The sclerotia have strong resistance to adverse environments and can survive in soil for several years, spreading through flowing water, irrigation water, rain splashes and fertilization. The disease is most severe in acidic soil, and hot, humid weather easily induces the disease. Infection begins in April to May, with the peak incidence from June to August. The disease develops rapidly, causing the affected orchid plants to rot, wither and die.
Control Methods
1. Orchid southern blight is prone to occur when the substrate is acidic (pH value less than 5.3), so mixing plant ash at a volume ratio of 1/10 into the substrate, or watering with 0.3% lime water to raise the pH value to around 6.5, can reduce the occurrence of southern blight, with obvious results.
2. Disinfect orchid substrate soil with 0.2% quintozene 500-fold solution or 50% carbendazim wettable powder 600-fold solution. You can also spray the root zone and soil with quintozene 500-fold solution or 70% thiophanate-methyl wettable powder 800-fold solution, or mix 50 grams of quintozene powder with 4 to 5 kg of semi-dry and semi-moist fine sandy soil and scatter it at the root and stem area of diseased plants, which can inhibit the spread and transmission of the disease.
3. In the rainy season from May to June in the south, soil humidity is relatively high, and southern blight is prone to occur on the pot surface. The plants should be quickly moved out of the orchid growing area for “isolation”, and the substrate should be pulled apart, the substrate contaminated with mycelium removed, and the diseased roots cut off. Spray with potassium permanganate solution 1000-fold for disinfection. You can also spray the root system and wounds with 70% thiophanate-methyl 1500-fold solution, and scatter fresh plant ash around the orchid roots, then cover with substrate to protect the roots. Water only after 2 to 3 days; if the substrate is wet, watering can be postponed for another 5 to 7 days. The control effect is good.
4. When orchid southern blight occurs, use medical chloramphenicol injection diluted 2000-fold in water and drench the diseased plants, once a day, for 3 consecutive applications. Once the disease occurs, the diseased leaves should be cut off, ventilation conditions improved, and the whole orchid plant soaked in 10% copper sulfate solution for disinfection. Nearby orchid plants should also be thoroughly sprayed, wetting the base and pot surface, spraying once a day for 2 consecutive applications, which can control the disease with good results.
5. After new orchid shoots grow out of the soil surface, spray with 0.05% chloramphenicol once a week for 2 to 3 consecutive sprays. If the potting soil is dry, this medicine can be applied as a drench to prevent bacterial infection. You can also water or spray with aspirin 1500-fold solution, which can enhance the immunity of orchid plants and prevent the invasion and spread of pathogens.
6. During the new shoot elongation stage and leaf expansion stage of orchids, you can choose medical penicillin, streptomycin, chloramphenicol, or a penicillin mixture diluted to 2000-fold solution, drench the diseased plants, and spray comprehensively, once every 3 to 4 days for 2 consecutive sprays. The control effect is good.
7. After orchids develop the disease, spray with 50% benlate wettable powder 1000-fold, or 50% carbendazim wettable powder 500-fold, or 50% thiophanate wettable powder 500-fold solution, or 70% chlorothalonil wettable powder 800-fold solution, once every 7 to 10 days for 2 to 3 consecutive sprays. The control effect is good.
8. After orchids develop the disease, spraying for control can be done before and after overcast or rainy weather. You can use 50% procymidone powder 500-fold, or 50% vinclozolin powder 500-fold solution, dufulin 500 to 600-fold solution, or 5% validamycin aqueous solution 300-fold, spraying the stems, leaves and pot surface. The control effect is significant.