Diagnosis and Integrated Control of main Diseases of Cymbidium

1 diagnosis of main diseases of Cymbidium

(1) Leaf spot

Leaf spot disease often occurs on the leaves of Cymbidium. In the early stage of the disease, the leaf tip of Cymbidium turned yellow at first, the light yellow disease spot appeared, and the surrounding disease tissue was yellowish green. With the development of the disease, the disease spot continues to expand and show irregular large spots, slightly sunken, the interior is light brown or grayish brown, the edge is slightly raised, showing yellowish brown. In the later stage of the disease, the leaves were withered and yellow, and gradually spread to the root. There are many small black spots on the back of the lesion. The pathogen of the disease is a fungus of the genus Stem. Pathogens usually overwintered on diseased tissue or diseased residual plants, spread with the help of Rain Water, air flow and irrigation water, and mostly infected from plant wounds. Leaf spot disease often occurs in summer. Poor air circulation, high temperature and direct light are all beneficial to the occurrence of leaf spot disease.

(2) White silk disease

White silk disease occurs near the soil of the orchid plant. After the disease, there was water-stained brown soft rot, white silky hyphae covered the diseased site, and the mycelium spread in the rhizosphere soil surface, mostly radiating, and sclerotia formed in the later stage. The sclerotia was white at first, then turned yellow, reddish brown to dark, and in severe cases, the base of the plant rotted and withered and died. The pathogen of the disease is Sclerotinia uniformis, the pathogen remains in the form of hyphae and sclerotia in the surface soil layer overwintering, saprophytic life, often occurs in summer with high temperature and high humidity. Bacteria check has strong resistance to adverse environment and can survive in the soil for 3 to 4 years.

(3) anthrax

Anthracnose mainly occurs on the leaves of Cymbidium. After the onset of the disease, the leaves appeared light brown or dark brown spots, which gradually expanded into round, oval or semicircular, with wheel spots, which were covered with black granules and gushed pink liquid when wet, which was a pile of conidia of pathogens. When anthrax is serious, the leaves wither and fall off. The pathogen of anthracnose is Alternaria. The disease occurs more often in wet and high temperature seasons, and it is easy to occur when watering is too wet, especially in the evening and when plants are placed too densely.

(4) soft rot

Soft rot mainly harms pseudobulbs and leaves of Cymbidium. At the initial stage of the disease, the leaves were damaged, the heart leaves and the base of the heart leaves showed dark green waterlogging-like disease spots, the diseased leaves rotted and became soft and sagging, spread to the root system to make it mushy, the center of the leaves fell off, and the whole plant died. The pathogen of soft rot is Euclid bacilli, the lesion begins from the base of the plant, and then the leaves begin to rot, and the leaves and stems rot into paste and stink. After 2 to 3 days, the disease part of the leaves shows sticky soft rot-like stem rot. The outer leaves were good, the heart leaves were rotten, the leaves and stem bases were good, the leaves rotted locally, and the whole leaves rotted and spread gradually within 12 hours, and the diseased part showed water-immersed leaf-rotting pathological changes, as well as rotten roots and leaves wilting. The root system showed purulent root-rotting disease. The pathogen of soft rot is mainly overwintering in the residue of diseased plant and soil. The disease is easy to occur in summer with wet rain, high temperature, poor ventilation and application of a large amount of unrotten fertilizer.

(5) Root rot

Root rot occurs in seeds, seedlings and adults of Cymbidium. If the seed is cold and humid after sowing, the germination time of the seed is prolonged, the radicle changes from brown to grayish brown, the depression becomes soft and rotten, and some rot to the endosperm, making the seed become an empty shell. Seedlings, adult plants infected, the roots become grayish brown or brown, in the later stage, only the epidermis, can not absorb water, serious roots all rot away. The pathogen of root rot is Fusarium oxysporum. The disease can occur all year round, such as high temperature, long-term wetness of basin soil, excessive fertilization, root injury, excessive watering after long-term drought and so on.

(6) Mosaic disease

Mosaic disease is characterized by chlorotic stripes or yellow-green stripes of different length in the mesophyll of Cymbidium, and the symptoms of young leaves are more obvious than those of old leaves. Mosaic disease is a viral disease, which is easy to spread when aphids, red spiders, shell insects and other pests harm Magnolia.

(7) Yellow leaf disease

The causes of yellow leaf disease of Cymbidium include: the infiltrative yellowing of the tip of young leaves is caused by too much watering for too long; the yellow tip of old leaves is caused by lack of water; the yellow tip of leaves and root burning are caused by excessive fertilization; the tip of the leaf turns yellow first and the new leaf yellow (8) sunburn disease.

Sunburn disease is a physiological disease, which mostly occurs in summer and autumn, and is caused by high temperature and strong light directly irradiating the leaf surface. The leaves of light ones turn yellow, while those of heavy ones become dehydrated and dry and die.

(2) Integrated control of diseases of Cymbidium

Timely removal of diseased leaves, diseased leaf sheaths and diseased plant residues, concentrated burning of diseased leaves and diseased plants, reducing the source of infection and avoiding the spread of pathogens. Change the soil at least once a year. The new soil should be loose and fertile to facilitate the development of fleshy roots of Cymbidium. At the same time, the basin soil should have good drainage and have a certain water retention capacity. Disinfect and sterilize new soil and flowerpots if necessary.

The new varieties of Cymbidium with disease resistance, high temperature resistance, cold resistance and excellent characters were selected. Generally speaking, chimera orchids are more susceptible than green orchids, thinner leaves are more susceptible to disease than thicker leaves, and glossy and waxy leaves are less susceptible to disease.

Strengthen the daily management of Magnolia. The main results are as follows: (1) increase the application of organic fertilizer, phosphorus fertilizer and potassium fertilizer, and properly control nitrogen fertilizer to make the plant grow healthily and improve the disease resistance of the plant. (2) keep good ventilation condition, add sunshade net in time in summer, avoid burning leaves by strong light, and take cooling measures such as wet and exhaust in time when high temperature is high. The temperature should be controlled at about 25 ℃. (3) Magnolia should be watered with magnetized water, Rain Water, snow water and live water, the water temperature is as close as possible to room temperature, and the pH value is 7.07.6. For young plants of Cymbidium, spray can be used to spray and water the leaves directly. When watering the seedlings, pay attention to the injection along the edge of the basin, so as not to pour water on the leaf surface and cause rotten heart at the base of the leaf. Generally, water is watered once a day in spring and summer, once every other day in autumn, and once every 3-5 days in winter. Usually, the relative humidity of the air in the shed is kept at 70%-80%, and the soil water content in the basin is 20%-40%. (4) isolate and clean up the infected plants in time to reduce infection. Remove the diseased part of the diseased plant that is still possible for treatment, disinfect the diseased part with 0.1% potassium permanganate solution for 5 minutes, then wash it, soak it in 50~100mg/ La-naphthylacetic acid solution for several hours, replant it in disinfected wet sand or vermiculite, control the amount of water, wait for it to take root again, and then transplant it into nutrient soil.

Chemical methods were used to control the diseases of Cymbidium. (1) at the initial stage of the disease, the whole plant was sprayed with 1000 times of carbendazim wettable powder, 1500 times of methyl thiophanate wettable powder, 1000 times of 50% arsine zinc thiophanate wettable powder, 65% methomyl zinc wettable powder or 25% methomyl wettable powder. Use medicament alternately and spray evenly to avoid drug resistance. (2) cut off the diseased leaves of Magnolia in time, and smear the wound with wettable powder such as carbendazim, methyl parathion, arsine zinc thiram, etc., which can effectively prevent the spread of the disease. (3) when the disease is serious, the basin soil is disinfected with 600 times solution of 50% carbendazim wettable powder. (4) prevent and control insect pests such as shell insects, red spiders and snails, avoid leaf trauma and reduce infection. The way to control shell insects is to scrub the damaged leaves with soapy water or spray them with 50% phoxim EC or 50% malathion EC 1000-1500 times. The way to control red spiders is to manually capture or spray 1000 times of 40% omethoate EC or 1000-1500 times of 40% diclofenac EC, once a week, 23 times in a row. The snail control method is to manually capture or spray 3000 times 50% methomyl wettable powder or 2.5% deltamethrin EC 2000 times twice.