Using fertilizer to prevent disease and pests, how can the effect be improved?

One of the biggest problems that needs to be dealt with during the planting process is disease prevention and pest control, and we can solve this problem through rational fertilization. So, how can the effect of using fertilizer to prevent disease and control pests be improved?

1. How can the effect of using fertilizer to prevent disease be improved?

Rational fertilization can not only promote crop growth, but also reduce the occurrence of diseases. For example, when wheat is at the jointing and heading stages, spraying 1% and 3% superphosphate solution respectively can improve resistance to stripe rust and reduce the disease; increasing the application of potassium fertilizer can improve the resistance of rice to rice blast, rice sheath blight, cotton fusarium wilt, potato late blight, tomato leaf spot, etc.; copper fertilizer can improve the resistance of tomatoes to leaf mold and sugar beets to brown spot, etc. 

The reason fertilizer can prevent disease and enhance crop disease resistance lies in five aspects: 

① Directly killing pathogenic bacteria. For example, calcium cyanamide and the intermediate substances it transforms into have special toxicity to pathogens; zinc has the ability to directly poison pathogens and has a fixing effect on viruses, hindering the upward movement of pathogens; copper and manganese are also toxic to pathogenic bacteria;

② Enhancing the ability of host crops to resist pathogen infection. For example, after applying silicon fertilizer, epidermal cells can become silicified; applying potassium fertilizer can promote the formation of cellulose and lignin, making it harder for pathogens to invade the plant; appropriate amounts of calcium, boron, and zinc can improve the stability of epidermal cell membranes and reduce the exudation of nutrients outward, thereby reducing pathogen infection;

③ Promoting the formation of phenolic compounds in plants. It is generally believed that crops or varieties with high phenolic content have stronger disease resistance, because phenols have a bactericidal effect. Appropriate application of potassium fertilizer can increase the phenolic content in millet leaves and reduce damage by Corynebacterium, but excessive application of nitrogen fertilizer lowers the phenolic content and makes plants more susceptible to disease;

④ Promoting protein formation. It is generally believed that glutamic acid, aspartic acid, and their amides are good nitrogen sources for pathogens and are conducive to pathogen reproduction. Increasing the application of potassium fertilizer can promote the formation of protein from soluble nitrogen, thereby improving crop disease resistance. Many trace elements such as boron, zinc, molybdenum, and manganese can promote protein synthesis and reduce amino acid content in the plant. This is an important reason why appropriate application of trace elements improves crop disease resistance;

⑤ Promoting starch formation. Crop disease resistance is closely related to starch content in the plant, because when starch content is high, soluble nitrogen content is low, and the carbon-to-nitrogen ratio is large, which is unfavorable for pathogen reproduction, so disease is less likely to occur. According to research, the starch content in rice is lowest at the tillering stage and heading stage, and this is exactly when rice blast is prone to occur. Phosphorus and potassium fertilizers can promote photosynthesis and starch formation, thereby enhancing disease resistance. Trace elements such as iron, manganese, zinc, and copper are indispensable for the normal progress of photosynthesis. The formation of high-molecular carbohydrates is also inseparable from trace elements. When trace elements are lacking, crop disease resistance weakens.

To improve the effect of using fertilizer to prevent disease, you can start from the following three aspects:

① Pay attention to the balance among nutrient elements. Combine nitrogen, phosphorus, and potassium fertilizers, and use macronutrients, secondary nutrients, and trace elements together to enhance the disease resistance of plants;

② Increase the application of organic fertilizers. Organic fertilizers contain large amounts of microorganisms and have an antagonistic effect on diseases, especially soil-borne diseases;

③ Change the soil pH. Many soil-borne pathogens are fungi and are relatively sensitive to ammonia. Therefore, applying ammonia water has a strong bactericidal and disease-preventing effect on wheat take-all fungus, cotton Verticillium wilt fungus, and cotton Fusarium wilt fungus. 

2. How can the effect of using fertilizer to prevent pests be improved?

In production practice, people have found that some fertilizers can not only promote crop growth, but also play a role in pest prevention. For example, silicon fertilizer has a relatively good control effect on rice borers, rice planthoppers, and bean borers; after spraying superphosphate on cotton, it can control cotton bollworm; applying manganese can reduce damage by barley aphids, grape aphids, and sugarcane root borers; applying boron can reduce mite damage; ammonium bicarbonate also has an insecticidal effect. 

The reasons fertilizer can prevent and control pests mainly include the following three aspects:

① Some pests are repellent to the chemical components of certain fertilizers. For example, cotton bollworm has this kind of repellency to the phosphorus element in superphosphate;

② After fertilization, the insect resistance of crops is enhanced. For example, after applying silicon fertilizer to crops, epidermal cells can become silicified, making it harder for insects to invade; copper and boron enhance crop insect resistance by participating in lignin formation, etc.;

③ Some fertilizers have strong stimulating, corrosive, and fumigating effects and have insecticidal ability. For example, ammonium bicarbonate can very easily kill some small pests with weak tolerance. 

Using fertilizer to prevent pests should also pay attention to methods. For example, when using superphosphate to control cotton bollworm, it is necessary to grasp, according to the growth and occurrence characteristics of cotton bollworm, that the repellency of cotton bollworm to phosphorus occurs during egg laying, so the fertilizer should be applied during the occurrence periods of the second, third, and fourth generations of cotton bollworm. Generally, a 1% superphosphate extract is used for foliar topdressing to drive cotton bollworms to gather and lay eggs in one place, and then they are eliminated together. In this way, cotton bollworm can be controlled while also promoting early maturity and high yield of cotton.