There are small black spots on the back of orchid leaves, how to deal with them?

In orchid cultivation, if we want to raise strong and disease-free orchid seedlings, we must first face infectious diseases, which can be divided into four categories: fungal, bacterial, viral and nematode. These pathogens can spread through certain ways and spread to each other, from less to more, from point to area. The pathogens of infectious diseases of orchids are mainly fungi, followed by bacteria and viruses, and insect pests are few. There are only a few fungi that usually harm orchids, such as Alternaria, Phytophthora, Fusarium, Rhizoctonia, Alternaria, Cercospora, etc., which survive by parasitism or saprophyte. The disease occurs under suitable conditions.

The pathogens infecting orchids first come into contact with the infectious parts of host plants, and begin to propagate and expand in orchids (mainly aboveground tissues), and then occur pathogenicity, which is usually divided into three stages: invasion, incubation and disease. The period from the invasion of the pathogen into the host plant to the establishment of the parasitic relationship is called the invasion period; from the establishment of the parasitic relationship to the beginning of the symptoms is called the incubation period; and the period after the symptoms appear is called the onset period. Pathogens, hosts and suitable environmental conditions are indispensable, which is called the triangular relationship of plant diseases. To put it simply, it is latent in winter, sick in spring and summer, and latent again in winter. Such as Fusarium, Alternaria overwintered in diseased leaves and soil in the form of mycelium and conidium disk, and the conidium disk was used as the initial and re-invading seed body to complete the disease process in the coming year.

The invasion of bacteria is related to environmental conditions, among which the relationship between humidity and temperature is the most important. In a certain range, humidity determines whether spores can germinate and invade, while temperature affects the speed of germination and invasion. The temperature in winter is low and the humidity is lower than that in spring and summer. At the same time, when the orchid enters the dormant period, the invasion rate of pathogens is slow, but it does not mean that it can not cause harm to the orchid. In addition, there is also a certain relationship between light and bacterial invasion. For pathogenic fungi which are easy to invade from stomata, light can determine the opening and closing of stomata, thus affecting the invasion. We found that the orchid plants with good lighting had strong disease resistance, while the orchid plants with poor light were easy to get infected because of the open stomata. So drying orchid in winter is advocated by the orchid family.

Pathogens invade the orchid tissue to form a local or sporadic infection, which is called local infection, and local infection is easier to treat. When local infection spreads, it causes whole plant infection, which is called systematic infection. There was already some trouble with the treatment at this time. Therefore, early detection and early governance should be achieved. During the growth of orchids, most of the irregular diseases have been controlled by us, and a few, such as soft stem rot, have also been cleared out of the orchid house. After the beginning of winter, there are few remaining bacteria that can threaten the orchid line, so the effect of disease prevention in winter is very ideal.

Another favorable factor is that the bacteria are in a state of inhibition due to the temperature in late autumn and early winter. Orchids gradually changed from luxuriant reproductive growth to dormant form, bacteria, fungi, viruses, nematodes gradually dormant, resistance greatly weakened, all kinds of efficacy can be brought into full play, as long as the pathogen is pursued, the good effect will be very obvious in the coming year, and it is the easiest time for orchid disease management in the coming year.

What is Qingyuan Qingyuan in winter?

In winter, because the orchid room is closed, the air can not be replaced, this stable and sealed environment is very beneficial to the pathogen overwintering, although the winter temperature is very low, but the vitality of the pathogen is very strong, and the closed orchid room due to daytime sunlight radiation, the temperature will still rise to 15. Above C, the bacteria will still reproduce slowly, and the bacteria will be in a state of inhibition after the temperature drops at night, so again and again, rising day and falling night. This year is also a rare warm winter, in mid-November, the lowest temperature is still hovering in more than ten degrees, it is already very cold at this time in previous years. If such a warm winter condition is maintained, the growth of pathogens is greater than the loss, and the accumulation is still considerable. It should be noted that due to the improvement of our orchid cultivation facilities, that is, in the coldest three or nine days, whether it is balcony, orchid room, Jiangnan, Saibei, the temperature of our orchid cultivation site will not drop to 5. Below C. In particular, the maintenance of the orchid, lotus petal, ink orchid type of cold fear of the orchid room.

Although the activity ability of pathogens is weak in winter, it will not cause too much harm to orchids, but if drugs are not used regularly and quantitatively, the bacteria will accumulate to a certain extent and proliferate rapidly in early spring. Therefore, it is necessary to spray fungicides several times regularly after winter.

At the same time, although the temperature in winter is low, but because we close the orchid house, the humidity is on the high side, Botrytis cinerea can occur under the condition of low temperature and high humidity, and the calyx petals appear waterlogged disease spot, and when the petals rot seriously, it is said that it is only found in Phalaenopsis and Cymbidium in China. The incidence of Cymbidium is ominous, but as Botrytis cinerea is a common disease of flowers in winter, the author still advocates caution.

New orchid plants in spring are prone to black spot, brown rust, crown rot and so on. These symptoms are caused by the accumulation of pathogens in winter. Black spot spends the winter in withered leaves or soil with mycelia or conidia, and the temperature is 10. At C, the spore germination rate could reach 50%, and the next year it was spread in February and March with the help of spring rain, and the control drug was 1000 times of mancozeb. Brown rust does great damage to orchids, and prevention and control is difficult. Prevention is more important than treatment in order to effectively control the disease. The control effects of copper sulfate, Shiduqing, boric acid and lice Jingjing (containing strychnine and treating shell insects) were not good. After the occurrence of brown rust, it is difficult to spread and control, but as long as we avoid extensive management, properly control the number of orchids and shorten the flowering period, it is helpful to improve plant disease resistance and reduce the chance of pathogen invasion. The prevention of topiramate and trimethoprim in orchid plants without disease. Try to avoid using chemicals containing "copper" or other heavy metal ions.

The pathogen of overwintering causes the first infection after the beginning of spring after the new generation of plants begins to grow. In fact, once the pathogen is infected successfully, it is little affected by external factors, that is to say, contact fungicides can do nothing about it, so it is reasonable for everyone to advocate prevention. Understand the above principles, we can do active prevention and treatment, in addition to regular quantitative drug prevention during the growth period, the removal of pathogens in the dormant period can achieve twice the result with half the effort.

How to clean up the orchid garden

1 the first thing to prune is to prune diseased and withered leaves and put an end to parasitic places of fungi. When cutting off the diseased leaves, you should pay attention to the action gently, accurately and decisively, and carefully put the cut diseased leaves into the plastic bag, in order to prevent the spores from flying away after vibration, and the cut diseased leaves should be destroyed centrally.

2 on a clear day, orchid friends start to clean up the garbage, dust and weeds in the orchid house, eliminate pathogens and intermediate hosts, and try to clean up the dust outside the orchid basin.

(3) after disinfecting and clearing the garden, the site should be disinfected first. Before the orchid is placed in the room, the orchid cultivation site should be disinfected in advance. The surface can be evenly sprayed with 50 ml of formalin or potassium permanganate and 10 kg of water per square meter, or the surface walls can be sprayed with 50% carbendazim wettable powder or 36% methyl thiobacillus suspension 500 times. Then close the doors and windows and open the windows for about 10 days to make the gas evaporate.

Secondly, do a good job of seedling disinfection. Strong seedlings should be selected for introduction in autumn, and disease and weak seedlings should be eliminated. Avoid bringing wolves into the house. The newly introduced varieties or downhill grass were first treated with drugs. Many people soaked in potassium permanganate solution with 1000-800x solution for 15 minutes. Potassium permanganate was a strong oxidant, which released new ecological oxygen in case of organic matter, so that the active gene of protein in the bacteria was oxidized and denatured, and then played a role in sterilization. It is a good fungicide. Low concentration of potassium permanganate has convergence effect, high concentration of potassium permanganate has disinfection and antiseptic effect, but its disinfection effect is superficial for a short time.

4 replacement of plant material for the orchid plant which is normally managed but does not grow in quantity, it is very likely that the plant material has been infected with the pathogen, because a large part of the pathogen is parasitic and in the soil. We pour it into the pot during the dormant period of the orchid to check the root system and so on. If there is black root and rotten root, it shows that the root system has been infected by bacteria, and if root rot occurs, we have to change the plant material, disinfect and replant it. In order to improve the growth environment of Langen. At the same time, the orchid basin was injected once or twice. What needs to be explained here is that root irrigation is only aimed at the germs in the plant material, and if the bacteria have invaded the orchid root, no matter how good the medicine is, because the root skin of the orchid root is thick, the liquid cannot get in, and the disease root can only be cut off with scissors, and the hands cannot be soft, otherwise the trouble will be endless.