What Are the Classifications of Fruit Tree Fungicides? A Detailed Explanation of Common Agents and Their Effects
In the process of fruit tree cultivation and production management, we often encounter various fruit tree diseases. When controlling various diseases on fruit trees, we also frequently use various fungicides. Understanding the classifications of fungicides and their effects will be of great help for the selection and use of agents for fruit tree disease control in the future.
Classification of fungicides: A fungicide is an agent that inhibits or kills fungi, bacteria, or diseases. According to the properties and effects of the agent, it can be divided into:
1. Protective agents Before the pathogen reaches the host plant or invades the host, the agent is applied to the plant surface to prevent pathogen spores from germinating or to kill spores that are germinating, thereby protecting the plant from pathogen damage. Examples include Bordeaux mixture, zineb, and Tuzet. They are generally non-water-soluble, can withstand wind and rain washing and erosion, and provide relatively long-lasting protection.
2. Eradicant agents After a plant becomes diseased, they are applied to the plant surface to kill fungi that have already entered but whose bodies are still mostly attached to the host surface. For example, powdery mildew fungi are often controlled with sulfur-based agents. Eradicants are mostly used during the dormant period of crops, such as the whitewash applied to fruit trees in winter or high-concentration lime sulfur mixture to kill overwintering pathogens. Some eradicants can also be used to disinfect farm tools and soil to kill pathogens and nematodes therein, such as formalin.
3. Systemic fungicides The agent can penetrate through the plant epidermis into the internal tissues and, within the plant body, spread and persist along with translocation or produce metabolites, so as to protect the plant from pathogen invasion or to treat disease, such as carboxin, benomyl, and thiophanate. These agents resist rain washing and are effective against deep-seated pathogens, but they also easily cause pathogen resistance.
4. Antibiotic fungicides These use the metabolites of some fungi to kill or inhibit other fungi. They are also called biological agents, such as blasticidin and kasugamycin.
According to the above classifications of fungicides, in the process of fruit tree cultivation and management, we should analyze the various diseases on fruit trees and, based on the purpose of control, the timing of disease control, and the season, carefully select various fungicides and apply the right remedy, so as to achieve the goal of chemical control of fruit tree diseases.
Methods of using fruit tree fungicides:
1. Plant surface application method Applying the agent to the plant surface is called plant surface application. Five methods are commonly used: spraying, dusting, trunk painting or whitewashing, root drenching, and smearing wounds.
2. Agent treatment of seeds and seedlings method Treating seeds, seedlings, scions, cuttings, and other propagation materials with agents to eliminate pathogens attached to the surface of these materials or inside them, ensuring that planting materials do not introduce dangerous diseases.
3. Soil agent treatment method Applying fungicides or nematicides to eliminate plant pathogens or pathogenic nematodes in the soil is one of the important measures of chemical protection. This method is mostly used to control fruit tree root diseases or soil-borne vascular diseases, nematode diseases, and so on.
Precautions for using fruit tree fungicides:
Choose the right spraying time
Spraying too late not only causes waste but also reduces the control effect. When using fungicides, the agent should be applied in a timely manner according to the occurrence patterns of different crop diseases and the specific conditions of disease occurrence. Generally, the best application time for fungicides is before disease onset or in the early stage of disease.
Be cautious about mixing agents
Many fungicides are alkaline pesticides, so they cannot be mixed with insecticides that easily decompose and become ineffective when encountering alkaline substances. For example, Bordeaux mixture and lime sulfur mixture are alkaline and cannot be mixed with dimethoate, 1605, dichlorvos, and others. Doing so will cause the insecticidal microorganisms to lose physiological activity or insecticidal ability and become ineffective.
Use pesticides scientifically
The number of fungicide sprayings is mainly determined by the length of the residual effective period of the agent and meteorological conditions. Generally, spray once every 10---15 days, for a total of 2--3 times. If it rains after application, promptly re-spray. When spraying, the droplets should be fine and uniform, and every effort should be made not to miss any area.
Guard against phytotoxicity
Generally, seedlings and the booting and flowering stages are prone to phytotoxicity. In addition, applying the agent under conditions such as high temperature and drought, strong sunlight, heavy fog, or high humidity is more likely to cause crop phytotoxicity.
In addition, when using fruit tree fungicides, phytotoxicity problems must be strictly prevented. For example, seedlings and the booting and flowering stages are prone to phytotoxicity, and during these periods it is best to use fungicides with caution.