How to prevent and control anthracnose of orchid

The harmful symptoms, pathogens, characteristics and control methods of orchid anthracnose are introduced as follows:

1. Symptoms the symptoms of orchid anthracnose are complex, and the larger ones can be divided into three types: round spots, round patches and withered leaves. When harming orchid plants, they are mainly divided into two types according to the size of orchid seedlings: one kind infects the tender leaves of seedlings, which first forms brown dots at the base of the leaves, then expands to form wheel spots, and when the heart leaves rot seriously; the other kind infects the leaves of old seedlings to form round and oval disease spots on the leaf surface, and when the leaf edge occurs, semicircle disease spots are formed at the initial stage: the disease spots form reddish brown patches at the initial stage of the disease. In the later stage of the disease, the disease changes from brown to grayish white, the edge is dark brown, and there is a chlorotic halo around it. The diameter of the disease spot is mostly 0.1mur0.5 cm. In severe cases, the disease spots are connected to each other to form a patch. If the disease is not effectively controlled, the leaves die gradually from top to bottom. In the later stage of the disease, the disease department produces whorled small black dot conidial discs. When the air humidity is high, the production department produces whorled small black spots pink colloid, that is, the transmission source of pathogen re-infection-conidium.

2. The pathogen of the disease belongs to fungi, the behavior is ascomycetes, the state is half-known bacteria, in general, the anamorph is the main pathogen harmful to orchids.

3. Transmission route and incidence regularity in Dali City, the disease is mainly overwintered by mycelium and molecular spores on diseased plant residues and diseased plants. in Dali City, the disease can occur in all four seasons. Conidia are mainly transmitted by wind, rain (mainly watering and spraying indoor) and insects, such as sharp-eyed bacteria and mosquitoes. Under the condition of water droplets on the leaf surface, the conidia are easy to germinate and produce invading filaments, which invade directly from the cuticular layer on the surface of orchid leaves, and can also invade from wounds and air vents. When the temperature is about 20 ℃, symptoms can be shown in about 15 days. Because the disease can be transmitted through air circulation, the orchids in the same orchid garden are easy to infect each other.

4. Characteristics of the disease

4.1 the occurrence of the disease is related to cultivation management. The disease can occur all the year round in Dali City, in which the disease is more serious in spring and autumn, and the severity of the disease in summer is mainly related to cultivation management. The summer (June-August) in Dali City is the rainy season, when the air humidity is relatively high. If water is sprayed continuously to the orchid leaves in the orchid garden, the disease tends to aggravate in summer; on the contrary, under the condition of natural air humidity, if the ventilation is strengthened and the amount of spraying water is reduced, the occurrence of the disease is not very serious. In addition, the investigation showed that the disease was more serious in orchid orchard with poor cultivation and management, such as fine basin soil, soil consolidation, excessive watering, poor root system, partial application of nitrogen fertilizer and poor ventilation.

4.2 the orchid seedlings cultivated in the greenhouse related to the change of cultivation sites are sold directly to the natural growers on the balcony with moisturizing conditions without seedling treatment, in addition to the dehydration and drying of leaves, orchid anthracnose is also prone to orchid anthracnose. The typical symptom is that the orchid leaves die slowly from top to bottom.

4.3 it is related to the strength of orchid plants, in general, orchids with strong growth, good roots, adequate nutrition and balanced orchids are not easy to get sick, and poor orchid seedlings are easy to get sick because of their weak disease resistance. On the contrary, the orchid seedlings with poor root system and poor growth are easy to get sick because of their weak disease resistance.

4.4 related to the time of introduction and domestication, the orchids planted in Dali are mainly lotus orchids. After wild orchids are raised at home, they have high seedling rate, strong growth and strong disease resistance in the first few years, but after years of cultivation, the wild orchids degenerate and the disease resistance weakens, and the incidence tends to be aggravated. The most typical is Xiaoxue, a famous product of Yunnan orchid, which has been domesticated for hundreds of years and is most prone to orchid anthracnose.

4.5 related to the species of orchids, in general, the species with thick and hard leaves and those with erect leaves have strong disease resistance, such as tiger orchid and iron bone in Jian orchid, etc., while lotus petal orchids, spring orchids and green orchids, which are mainly planted in Dali, are more susceptible to the disease: the famous products in lotus petal orchids are more susceptible to this disease because of excessive seedling division and weaker growth orchids.

5. Pathogenic conditions of orchid anthracnose

Dali City is located in the low-latitude plateau, warm in winter and cool in summer, not easy to appear the bad conditions of high temperature and hot heat and ice and snow, so it is a good place to cultivate orchids naturally. However, after the orchid was introduced indoors, due to different cultivation and management conditions, the disease resistance of orchids weakened, and the pathogenicity of pathogens was strong, so the disease was more common in Dali City. It is observed that the following conditions are satisfied: that is, the average temperature is 20 ℃-25 ℃, the air humidity is more than 80%, and the humidity of the basin soil is often more than 90%. Under the conditions of poor ventilation, insufficient light, partial application of nitrogen fertilizer, and often spraying water to the leaves, the disease is easy to occur.

6. prevention and control measures

Orchid anthracnose is the most common disease on orchids, but the harm to orchids is not as serious as soft rot and stem rot. The biggest difference between the two is that the former mainly harms leaves and does not cause orchid plant death in a short time, while the latter mainly harms pseudobulbs, which can kill orchid plants within 7 days. Therefore, the prevention and control of orchid anthracnose, as long as good prevention and treatment measures, the disease can be controlled.

6.1 strengthening cultivation management in view of the incidence conditions of the disease, the core of preventive measures is that orchid sites should be ventilated and transparent, orchid plants should be ventilated and permeable, proper light should be maintained, pot soil plants should be moist but not wet, and it would be better to be dry: in fertilization, appropriate application of more phosphorus and potassium fertilizer, less nitrogen fertilizer, combined application of the three. Placed between orchid pots should not be too dense, in order to reduce the chance of leaf friction and reduce wounds: the root cause of orchid disease, except for pathogens and weak disease resistance of orchid plants, is generally caused by high temperature, high humidity and lack of ventilation. On cultivated orchids, we should closely focus on the above aspects to improve the environmental conditions of orchids.

6.2 cutting off diseased leaves and destroying them in time can effectively reduce the harm of the disease to orchid plants, reduce the amount of bacteria in orchid cultivation places, and reduce the incidence of disease for orchid plants without disease, because the disease can be airborne and can not be controlled by orchid farmers. Reducing or eliminating the source of bacteria is the best protection for orchids in the orchid garden.

6.3 foliar spraying is strictly prohibited for diseased orchid plants, which is not particularly emphasized in general orchid books, but from the author's practice, it is very important to control blue disease. This is due to the fact that under the condition of high leaf humidity, the disease is conducive to the further expansion of the disease spot and produces a large number of molecular spores, which are easy to germinate and spread to healthy orchids through air, water droplets and insects, causing the disease of other orchid plants. In orchid planting practice, during the peak period of the disease, the orchid is sprayed with water once, and after a few days, the disease spot will increase or the leaf tip disease will expand downwards. I believe that many orchids will have this experience.

6.4 the medicament prevention and treatment of the disease mainly starts from two aspects, namely, the prevention in peacetime and the treatment in the early stage of the disease. The following agents can be selected: 40% Baikodi wettable powder 1500 times: 10% Shigao granules 2000 times: 50% carbendazim powder 2000 times, 70% methyl topiramate powder 1500 times.

Usage: choose one of the above agents each time, use alternately, prevention can be prevented and treated once a month in peacetime: after discovering the disease of orchid plant, it is necessary to prevent and cure the diseased plant in time, once every 10 days, 3 times in a row, and then carry out targeted prevention and control measures according to the condition. Among the above agents, 50% anthrax powder has special effect on orchid anthracnose, once every 7 days-10 times, 3 times in succession, the control effect is more than 90%, generally can effectively control the harm of the disease; when there are more orchids, it can be sprayed with water. Less orchid, or particularly precious orchid disease, you can choose 50% anthrax Ling powder 50 times solution (1 gram of medicine to 50 grams of water), soak in the solution with a brush, directly apply to the disease spot, both sides, once every 7 days, three times, the special effect on anthrax, can control the disease spot no longer expand, and kill the disease bacteria.

In a word, orchid anthracnose can be prevented and treated, not as difficult to control as soft rot and stem rot.