In the normal growth process of rice, plants may face obstacles 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 farming practices, these issues can often be confused with one another, making it difficult to implement effective countermeasures. The following section outlines recent methods for identifying the "Four Evils" in rice fields and provides practical strategies for their prevention and control.
1. Methods for Identifying the Four Evils in Rice Fields
1.1 Water Damage
Water damage is typically categorized into three main types:
1.1.1 Water Quality Damage: This occurs when irrigation water is contaminated with harmful substances that are unsuitable for rice growth. Symptoms include uniform seedling damage, dark red or dark green leaves, unopened heart leaves, short new roots, floating bubbles on the water surface, pale green or light brown water, and a dark brown, smelly soil.
1.1.2 Waterlogged Damage: This happens when excessive irrigation is applied without proper drainage, especially after applying large amounts of organic fertilizer. High temperatures above 35°C can worsen the condition. Affected plants show purple spots on leaves, which spread from the top down, along with weak root systems and blackened roots. The soil becomes soft and dark black, and bubbles may rise from the water, accompanied by a foul odor.
1.1.3 Water Deficiency Damage: This occurs when the field is too dry, causing the upper leaves to turn from tender green to dark green, while lower leaves die prematurely. Cracks appear in the topsoil, and the surrounding area is heavier than the center of the field.
1.2 Fertilizer Damage
Fertilizer damage results from improper application or adverse environmental conditions. Common symptoms include white patches on the upper leaves, which may lead to leaf breakage within 2-3 days. This is often caused by using ammonium bicarbonate without mixing it with enough fine soil, resulting in ammonia gas burning. Another symptom is yellowing of middle and lower leaves, often seen in shallow or no water layers, particularly when nitrogen fertilizer is applied at high temperatures.
1.3 Phytotoxicity
Phytotoxicity occurs when pesticides are used improperly, sometimes mimicking disease symptoms but not spreading once they appear. It can be divided into two types:
1.3.1 Inadequate Use of Insecticides and Fungicides: This leads to purple-red discoloration at the tips of leaves, gradually fading towards the base. Severe cases may result in fusiform-shaped lesions, with the most affected leaves being the second, third, and fourth ones.
1.3.2 Misuse of Herbicides: For example, glyphosate misuse at low concentrations can cause growth stagnation, dark green early leaves, and dwarfed plants. At higher concentrations, the leaves turn brown, and the plant eventually dies.
1.4 Diseases
Diseases such as rice leaf mites, sheath blight, and rice smut can cause abnormal symptoms in plants. These symptoms usually start scattered and spread over time, worsening in severity. Some diseases, like stripe leaf blight and dry tip nematode disease, are more challenging to control with chemical treatments.
2. Prevention and Control Measures for the Four Evils
2.1 Water Damage
For water quality damage, it's crucial to test irrigation water before use. If contamination is detected, stop irrigation immediately and drain the field. Replenish with clean water 2-3 times to flush out contaminants. For waterlogged damage, ensure timely drainage and maintain a shallow water layer (1-2 cm) after the soil solidifies to promote healthy growth. For water-deficient damage, provide adequate irrigation to meet the plant’s physiological needs.
2.2 Fertilizer Damage
Avoid spreading ammonium bicarbonate directly on seedlings; instead, apply it deeply to improve nutrient absorption and prevent damage. When applying urea, maintain a water layer of about 1.5 inches. Avoid shallow water during high temperatures, and if damage occurs, irrigate immediately.
2.3 Phytotoxicity
During pest control, follow recommended dosages and avoid applying pesticides at high noon. Always check labels before using any product to prevent herbicides from being mistaken for insecticides. Store pesticides, fungicides, and herbicides separately with clear labeling.
2.4 Diseases
For susceptible diseases, focus on prevention and choose high-quality treatments. For refractory diseases, use resistant varieties and adopt methods like pesticide soaking to eliminate pathogens before they cause harm. Effective management is key to reducing losses and ensuring healthy rice production.
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