In the normal growth process of rice, plants may face growth restrictions due to external unfavorable factors, leading to abnormal symptoms. These symptoms are commonly referred to as the "Four Evils": water damage, fertilizer damage, phytotoxicity, and disease. In actual agricultural production, it is often difficult to distinguish between these issues, which can lead to inappropriate measures that worsen the situation. The following section outlines recent methods for identifying the "Four Evils" in rice fields and effective strategies for their prevention and control.
1. Methods for Identifying the Four Evils in Rice Fields
1.1 Water Damage: This type of damage can be categorized into three main types:
1.1.1 Water Quality Damage: This occurs when irrigation water contains harmful substances that are unsuitable for rice growth. Symptoms include uniform leaf discoloration (dark red or dark green), delayed emergence of new leaves, short roots, a layer of bubbles on the water surface, pale green or light brown water, and dark brown soil with an odor.
1.1.2 Waterlogged Damage: This typically happens when there is prolonged irrigation without proper drainage, especially after applying large amounts of organic fertilizer under warm weather conditions (above 35°C). The soil becomes anaerobic, leading to purple spots on the leaves, root rot, and a foul smell from the field.
1.1.3 Drought Damage: This occurs when the soil is too compacted, causing poor root water absorption. Symptoms include dark green upper leaves, early death of lower leaves, cracked topsoil, and uneven moisture levels across the field.
1.2 Fertilizer Damage: This results from improper fertilization techniques or adverse environmental conditions. Common symptoms include white patches on the upper leaves, which may cause leaf breakage within 2-3 days. This is often due to the direct application of ammonium bicarbonate without mixing with soil. Another symptom is reddish-yellow discoloration of middle and lower leaves, which can occur when nitrogen fertilizer is applied in high temperatures without sufficient water coverage.
1.3 Phytotoxicity: This occurs when pesticides are used incorrectly or excessively, leading to symptoms that resemble diseases but do not spread once they appear. It can be divided into two categories:
1.3.1 Inadequate Use of Insecticides/Fungicides: Symptoms include purple-red discoloration at the leaf tips, which gradually fades. Severe cases show fusiform-shaped lesions on the leaves, with the heart leaf remaining mostly unaffected.
1.3.2 Misuse of Herbicides: For example, glyphosate misuse at low concentrations can cause stunted growth and dark green leaves, while high concentrations can result in browning and eventual plant death.
1.4 Diseases: These are caused by pests and pathogens. Common diseases include rice leaf mites, sheath blight, and rice smut, which spread over time. Refractory diseases such as stripe leaf blight and dry tip nematode disease are harder to control once infected.
2. Prevention and Control Measures for the Four Evils
2.1 Water Damage:
2.1.1 Water Quality Damage: It's essential to monitor irrigation water quality. If contaminated, avoid using it. If symptoms appear after accidental irrigation, drain the field immediately and replace it with clean water 2-3 times.
2.1.2 Waterlogged Damage: Drain the field in time during any growth stage, and reapply water after the soil has solidified to promote healthy growth.
2.1.3 Drought Damage: Ensure timely irrigation to meet the physiological needs of the plants.
2.2 Fertilizer Damage:
2.2.1 Avoid spreading ammonium bicarbonate directly; instead, apply it deeply to improve efficiency and prevent damage.
2.2.2 When applying urea, maintain a water layer of about 1.5 inches. Avoid shallow water layers when temperatures exceed 35°C, and if damage occurs, drain the field immediately.
2.3 Phytotoxicity:
2.3.1 Follow recommended dosages for pesticides and avoid spraying during high temperatures.
2.3.2 Check labels before using any product to prevent herbicide misuse. Store different types of chemicals separately and label them clearly.
2.4 Disease Management:
2.4.1 For susceptible diseases, focus on prevention and use high-quality treatments to ensure effective control.
2.4.2 For refractory diseases, implement preventive measures such as selecting resistant varieties and using appropriate pesticide treatments to eliminate pathogens before they cause damage.
By understanding and addressing these four common issues, farmers can significantly improve rice health and yield, ensuring sustainable agricultural practices.
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