How to prevent and control anthracnose in orchids? Pesticide and non-pesticide measures for potted orchids
Orchid growers all know that anthracnose is a common disease of orchids. Although it will not cause the orchids to be "wiped out entirely," it lingers persistently and is very difficult to cure completely. Below, let us look at comprehensive prevention and control measures for anthracnose in potted orchids.
I. Pesticide control of anthracnose
The most commonly used method for preventing and controlling anthracnose is pesticide control. This allows the chemicals to kill or inhibit the pathogen in large quantities within a relatively short time and quickly eliminate the threat of the disease. When using pesticides for control, the following 3 points must be noted:
(1) Choose appropriate chemicals for prevention and treatment. There is a particular way to choose chemicals for the prevention and treatment of anthracnose. The chemicals selected for prevention and treatment must be targeted. Generally speaking, some broad-spectrum fungicides such as Kocide (copper hydroxide), Thiophanate-methyl (thiophanate-methyl), and carbendazim are more suitable as preventive chemicals, while during the disease outbreak period it is better to choose some chemicals for treating anthracnose, such as Shibagong (prochloraz manganese salt), Kairun (pyraclostrobin), and Shigao (difenoconazole). Chemicals for prevention and treatment should be selected separately; it is not advisable to use the same chemical for both prevention and treatment.
(2) Winter control is indispensable. The pathogen of orchid anthracnose overwinters as mycelium in diseased leaves or soil, so spraying and drenching with anthracnose control chemicals in winter is essential, and this is crucial for eliminating dormant mycelium. In the process of preventing and controlling anthracnose, when diseased plants are found, the affected parts should be cut off promptly and burned.
(3) Avoid long-term repeated use of the same chemical. Long-term repeated use of the same chemical makes it easy for the pathogen to develop resistance and fail to achieve control results. Whether for prevention or treatment, several chemicals must be used alternately; it is not advisable to use the same chemical repeatedly over a long period. However, it is also not advisable to change chemicals too frequently. Each chemical must be used continuously 3 times before switching to another chemical.
II. Non-pesticide control of anthracnose
Spraying chemical pesticides, although it can achieve a certain effect in preventing and controlling anthracnose, often causes environmental pollution. Using non-pesticide methods to control orchid anthracnose can overcome the drawback of pesticides polluting the environment, and it is also beneficial to the growth and development of orchids. Below are some folk remedies for non-pesticide control of anthracnose.
(1) Quicklime aqueous solution. First use an appropriate amount of water to slake quicklime into powder form. Take the slaked quicklime powder and clean water at a ratio of 1:60 and place them in a container to soak. Take the clarified liquid and spray it on orchid plants and the orchid-growing environment to prevent and control anthracnose. Quicklime is alkaline and can also control southern blight.
(2) Chive juice. Mix chive juice and clean water at a ratio of 1:60, and use it to spray orchid plants. Spray 2 times per day, repeating for several days, to 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 to prevent and control anthracnose and soft rot.
(4) Vinegar. Spraying vinegar on orchid leaves can prevent and control anthracnose. Take 1 tablespoon of vinegar, pour it into 1 kg of clean water and mix, then use it to spray orchid plants. Vinegar can also be added when using pesticides.
The above are pesticide and non-pesticide control measures for orchid anthracnose. To prevent the pathogen from developing resistance, pesticide control and non-pesticide control can be used alternately. Practice has proven that the results are good, and everyone can refer to them.
Identification and control techniques for orchid anthracnose
Anthracnose occurs in all orchid-growing areas of our country, with damage being more severe especially in Tianjin, Shanghai, Nanjing, Guangzhou, Chengdu, Lianyungang, and Xi'an. When the disease is severe, it not only affects the normal growth of orchids but also causes entire leaves to wither and die. In addition to 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 broadleaf orchids, as well as many ornamental plants such as Dieffenbachia picta, violet, marigold, hibiscus, and osmanthus.
I. Symptom characteristics. Anthracnose mainly harms orchid leaves, and sometimes also infects stems and fruits. Leaf spots initially appear round or oval, with the center light brown or grayish white, the edges dark brown or blackish brown, and a chlorotic halo around them; later, black small dots appear on the lesions, scattered or slightly arranged in rings, and under humid conditions, orange-yellow sticky matter appears. As the disease develops, leaf spots can expand into irregular large spots several centimeters long, or the lesions can join together into patches, finally causing the leaves to wither and yellow. Leaf spots range in size from 3-20 mm, varying greatly. Stems and fruits affected show irregular or elongated dark brown lesions.
II. Disease occurrence pattern. The disease is caused by infection by several species of anthracnose fungi. The pathogen overwinters in diseased leaves, diseased leaf residues, and withered leaf-base bracts. In the following year, under suitable climatic conditions, it spreads via wind and rain and insects; it mainly invades plants through various wounds. It can occur almost all year round, but is severe in summer and autumn. For example, during the plum rain season in the south, or in autumn when typhoons bring torrential rain, orchid leaves are injured, or under high humidity and stuffiness, 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 the roots are easily damaged. Sticky, 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 that the plants are not damaged by freezing or frost, thereby enhancing their ability to resist disease. After being moved outdoors, they should be placed in a shade shed to prevent wind and rain damage, and at the same time the shed should have sufficient sunlight. Watering is best done by slowly pouring from the edge of the pot or by subirrigation, which can reduce the spread of pathogens splashed by water droplets from overhead watering. Flower pots should not be placed too densely. Fertilization of orchids should be scientific. As is well known, fertilizer for orchids should be decomposed rather than raw. Applying raw fertilizer very easily induces anthracnose. When potting, new soil should be replaced.
2. Remove infection sources: Promptly remove diseased leaves and their residues. Especially before bringing plants indoors in winter, thoroughly remove and burn or deeply bury diseased leaves on the plants and diseased residues in the pots, so as to eliminate infection sources and prevent the disease from spreading. In winter and spring, spray 0.5-1% Bordeaux mixture 1-2 times comprehensively on the ground, pot surfaces, and plants.
3. Chemical control: Before disease onset, spray 0.5-1% Bordeaux mixture, or 65% zineb wettable powder 600-800 times dilution, once every 7-10 days, which gives good protection. During disease onset, spray 50% carbendazim 800 times dilution or 75% thiophanate-methyl 1000 times dilution, both of which can control the spread of the disease.
4. Non-pesticide control methods: (1) Vinegar. Spraying vinegar on orchid leaves can prevent and control anthracnose. Take 1 tablespoon of vinegar, pour it into 1 kg of clean water and mix, then spray 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. Spray 2 times per day, repeating for several days, to 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 to prevent and control anthracnose and soft rot. (4) Quicklime aqueous solution. First use an appropriate amount of water to slake quicklime into powder form. Take the slaked quicklime powder and clean water at a ratio of 1:60 and place them in a container to soak. Take the clarified liquid and spray it around orchid plants to prevent and control anthracnose. Quicklime is alkaline and can also control orchid southern blight.
Editor in charge: Molika
Methods for preventing and controlling pests and diseases of tropical orchids
Pest and disease management:The causes of orchid diseases are mainly excessive watering, poor drainage, and lack of ventilation, while some are external infections.
Anthracnose: In the early stage, affected leaves show yellow-brown sunken small spots that form brown lesions outward.
Control method: Remove diseased leaves and improve ventilation in the orchid shed; in the early stage of disease onset, spray 50% carbendazim or 50% thiophanate-methyl 500 to 600 times dilution.
Spot rot: For many orchids, this is an extremely serious disease. The disease starts from the base of the stem and quickly spreads to the leaves and roots.
Bacterial soft rot: This is a devastating disease and is extremely contagious. It first appears as water-soaked dark green spots at the tips of leaves and then expands. The pathogen invades through wounds. Orchids that are easily infected include Cattleya, Phalaenopsis, and Cymbidium hookerianum.
Control method: First, do a good job of environmental sanitation in the orchid nursery, promptly clean up dead branches and fallen leaves, and eliminate and remove sources of the pathogen; when diseased plants are found, immediately cut off diseased leaves and burn them, and spray once every 7 days with 50% amobam 800 to 1000 times dilution, 70% thiophanate-methyl 700 to 800 times dilution, and 50% wettable carbendazim 1000 times dilution, used in rotation.
Rot disease: Caused by Pythium, generally harming seedlings; spray with copper sulfate or other sterilizing chemicals for control.
Black spot disease: Black spots appear on the leaf surface and gradually expand, causing more than half of the leaf to wither and blacken. It is generally caused by excessive watering and poor ventilation. Ventilation and drainage conditions need to be improved, and fungicides should be sprayed. When cutting off diseased leaves, the tools must be disinfected.
Viral disease: This disease is quite common in orchids, and no effective control method has been found so far, but adopting comprehensive preventive measures to control it is very effective.
Control method: Strictly select and plant virus-free tissue-cultured seedlings and seed-grown seedlings; promptly eliminate weeds in the shed to prevent and control the disease; when diseased plants are found, immediately pull them out and burn them; after contact with diseased plants, tools and hands should be disinfected promptly; pots and potting materials that have been used for diseased plants cannot be used again.
Scale insects: These are the most common pests of orchids, mainly parasitizing orchid stems and leaves. Scale insect eggs hatch into nymphs, and after a short period of crawling, they form a scale. Because scale insects have a waxy outer shell, ordinary pesticides have difficulty penetrating, making control relatively difficult. It is best to spray pesticide during the peak hatching period of the eggs. You can spray 50% omethoate emulsifiable concentrate, 50% malathion, 25% phosmet emulsifiable concentrate, or 80% dichlorvos emulsifiable oil, etc., at a concentration of 1000 times dilution, once every 5 to 7 days, continuously spraying more than 3 times.
Red spider mites: They occur in places with strong light, dryness, and high temperature.
Control method: In cultivation management, pay attention to ventilation and increasing humidity. For chemical control, spray 40% dicofol, 80% dichlorvos emulsifiable oil, and 40% omethoate 1000 times dilution, continuously spraying several times.
Whiteflies: Whiteflies are small and covered with waxy powdery material, which makes control difficult. Chemical control: spraying 2.5% deltamethrin, 10% permethrin, and 20% fenvalerate 2000 times dilution gives relatively good control results. Or 40% omethoate, 80% dichlorvos, and 50% malathion emulsifiable concentrate also have good control effects on adults and larvae.
Snails and slugs: When shiny transparent mucus trail marks are seen on the edges of pots and on benches, it indicates that these mollusks are active. Control method: Poison bait trapping and killing, using bran mixed with arsenic, trichlorfon, etc., scattered in places where these animals are active. Or spread quicklime or saturated salt water.