What are the strategies to control plant diseases?

Inoculation sources in the early stage of plant diseases include places where bacteria overwinter and overwinter, intermediate hosts, soil with bacteria, seeds with bacteria and other propagation materials and field disease centers. Applying pesticides to the inoculation source to eliminate or reduce the infection source of pathogenic bacteria is an important strategy to protect plants from harm. The effect of using this strategy to control plant diseases is related to the location, quantity and transmission route of inoculation sources. If only diseases spread through propagation materials such as seedlings and diseases spread through diseased heart, under relatively easy control conditions, the epidemic harm of diseases can be prevented economically and effectively by treating seedlings with chemical agents or using fungicides with eradication effect in diseased heart. For example, dithiocyanomethane, thiram and the like are used. For seed treatment, not only the cost is low, but also the effect can reach 95%. Long-term use of this strategy to eliminate the source of infection has completely controlled the seed-borne diseases of some cereal crops that were seriously prevalent half a century ago. However, diseases spread through soil, water, sick people, airflow or various ways will be difficult to be completely eliminated because of the complexity and huge number of pathogens, and the pathogens left after drug treatment of infectious sources are enough to cause epidemic harm and it is difficult to achieve ideal results. Such as wheat sheath blight, scab, powdery mildew, rust, rice blast, sheath blight, bacterial leaf blight, cotton wilt, verticillium wilt, vegetable bacterial wilt, downy mildew, apple and pear scab, etc. At present, most important soil-borne and air-borne diseases cannot be effectively controlled by eliminating the source of infection.

2. Treat the surface of plants or agricultural products that may be infected by drugs.

Apply pesticides before the host plants are infected by pathogenic bacteria, so as to kill the pathogenic bacteria, prevent the spore germination of fungi, or interfere with the interaction between pathogenic bacteria and the host, prevent the infection of pathogenic bacteria, and make the plants chemically protected. This is the most effective strategy to prevent and control most diseases of stems, leaves and fruits spread by air during storage. Generally, the medicine is evenly applied to the host plant or organ by spraying and soaking, so that a film of medicine is formed on the surface of the plant, thereby killing the spores of the pathogen or preventing the infection of the pathogen. Traditional fungicides, such as sulfur, basic copper sulfate, mancozeb and thiram, and modern selective fungicides, such as iprodione, kresoxim-methyl and systemic fungicide tricyclazole, are used in non-systemic fungicide, and plant diseases can only be controlled if they are applied before pathogen infection. Treating seeds with systemic fungicide such as triazole and difenoconazole can prevent soil-borne damping-off and airborne powdery mildew and rust at seedling stage.

3. Before pathogen infection, use chemicals to interfere with pathogenicity of pathogen or induce host to produce disease resistance.

The melanin inhibitor tricyclazole inhibits the biosynthesis of melanin in the appressorium of Magnaporthe grisea, making the appressorium lose the ability to invade the host, thus protecting plants. Active ester is a plant defense activator, which can prevent and treat many plant diseases such as fungi, bacteria and viruses by inducing the host to acquire disease resistance. Because it takes some time to induce host resistance, it is necessary to apply protective pesticides.