Citrus canker is a common and extremely serious disease in citrus production, which has a huge impact on the growth and yield of citrus. It is mainly manifested in leaves, branches and fruits, forming canker spots, causing a series of problems, such as leaf drop, dead shoots, fruit drop, etc., which significantly reduces the commerciality of fruits and brings heavy economic losses to fruit farmers (see Figure 1). Understanding the harmful location and development law of citrus canker disease is the first step in effective prevention and control.
The disease mainly occurs on leaves, shoots, stems and fruits, especially on young tissues, which can cause defoliation and fruit drop, which has a serious impact on the normal growth of plants and may even lead to plant death. The pathogen overwinters in the diseased tissues of leaves, shoots and fruits, and in spring, under suitable conditions, it spreads over short distances through wind and rain, contact between insects and branches and leaves, and also spreads long-distance through seedlings, scion and fruits with the fungus. A variety of factors affect the occurrence of diseases, including the disease resistance of the host variety, climatic conditions, agricultural technology level, and external wounds.
After understanding the law of disease hazards, we need to take practical and effective prevention and control measures. First of all, the key is to cut off the transmission route of the pathogen and reduce the presence of diseased branches and leaves, so as to reduce the pathogen base. This is essential for the prevention and control of ulcer disease. Specifically, we can prevent it by:
1. Grasp the key time points of medication:
In the shoot extraction stage of citrus, including spring, summer and autumn, choose the new shoot to grow 1-3cm for pesticide application, to avoid the young leaves and young fruit stage on the new shoot. At the same time as clearing the garden, spray the agent while cleaning the diseased branches and leaves to reduce the pathogen base.
2. Follow the principle of scientific and rational drug use:
For young tissues and sensitive periods, choose safe and well-mixed agents, inorganic copper, organic copper or antibiotics can be used to mix according to the actual situation. It is also important to use a reasonable dosage of the drug, and the dosage to be used should be selected within the range of safe dosage.
3. Scientifically select and mix agents according to local conditions:
There are a variety of options for the prevention and treatment of ulcer disease, including copper preparations, organic copper, antibiotics and microbial agents. Comprehensively consider climate, geography and other factors, select appropriate agents for mixed use to improve the prevention and control effect. Bacterial and fungal diseases are often mixed, so it is necessary to choose agents that are effective against bacteria and have a preventive effect on fungi. Copper preparations are an ideal choice because they have a broad bactericidal spectrum, are less resistant to development, and have a stimulating effect on plant growth.
4. Agricultural control:
In terms of agricultural control, it is recommended to establish disease-free nurseries and cultivate disease-free seedlings. The nursery should be located in a disease-free area or far away from the citrus orchard to ensure good isolation conditions. During the nursery period, once diseased plants are found, they should be immediately dug up and incinerated. In addition, pay attention to reasonable fertilization, increase potassium fertilizer, control the amount of watering, and ensure that the summer and autumn shoots are neatly pumped to reduce the chance of germ invasion. Regular pruning of diseased branches and leaves, cleaning up dead branches, fallen leaves and fallen fruits, and combining with other pests and diseases to control are also effective agricultural control methods.
5. Pesticide control:
In terms of pesticide control, disinfection of seedlings and scion is an important measure. Agricultural streptomycin soluble powder can be used to disinfect by soaking. In addition, in the shoot stage and fruit stage, choose the appropriate agent for spraying, maintain a certain frequency of prevention and control, you can choose copper ammonia aqueous agent, thiazobium copper suspension, etc.
Through the comprehensive application of the above multiple control measures, the occurrence and spread of citrus canker can be effectively controlled, and the normal growth and high yield of citrus can be guaranteed. In the specific implementation process, the control method should be selected scientifically and reasonably according to the characteristics of the local climate, soil and citrus varieties to achieve the best control effect.