The fruit trees should be promptly remedied after the occurrence of phytotoxicity
Pesticide injury can occur due to various factors, including the type of pesticide used, the formulation, application methods, and environmental conditions. Understanding these causes is essential for preventing damage to fruit trees and ensuring effective pest management.
1. **Pesticide Formulations and Properties**: The physical and chemical characteristics of pesticides play a major role in determining their potential to cause phytotoxicity. Inorganic compounds with high water solubility and low molecular weight are more likely to harm plants. For example, copper and sulfur-based products often cause leaf burn or discoloration. On the other hand, water-soluble formulations and microbial pesticides tend to be safer. Among different types, oil-based and emulsifiable concentrates are more hazardous compared to wettable powders, while granules and dusts are generally considered safer.
2. **Fruit Tree Sensitivity**: Different fruit tree species and varieties have varying levels of sensitivity to pesticides. For instance, peaches, apricots, and plums are highly sensitive to Bordeaux mixture during the growing season, regardless of the concentration. Pears, apples (especially Golden Delicious), hawthorns, and persimmons may also suffer from phytotoxicity when the lime content in Bordeaux mixture is less than twice the standard amount. Grapes are more vulnerable when the lime content is higher. Similarly, 45% dexamethasone can cause damage if diluted below 1000 times, with certain pear and apple varieties being more affected than others.
3. **Application Methods**: Improper use of pesticides, such as incorrect dilution, poor mixing, or spraying at the wrong time, can lead to phytotoxicity. High concentrations, especially when pests develop resistance, increase the risk. Uneven distribution of spray droplets or dusting can cause localized damage. Some pesticides should not be mixed together, as this can reduce effectiveness or even cause harm.
4. **Environmental Conditions**: Temperature, humidity, and light intensity significantly influence the likelihood of phytotoxicity. High temperatures and strong sunlight can enhance pesticide activity, making it easier for them to penetrate plant tissues. Excessive humidity can also contribute to damage. Spraying herbicides on windy days may result in drift, leading to unintended exposure.
**Symptoms of Pesticide Injury**
Phytotoxicity symptoms vary depending on how quickly they appear and their severity. They are generally classified into three categories: acute, chronic, and residual.
1. **Acute Phytotoxicity**: This occurs shortly after pesticide application, within hours or days. Symptoms include leaf spots, burning, chlorosis, yellowing, curling, wilting, and even death. Fruits may show deformities, discoloration, or premature dropping. Flowers may become scorched or discolored.
2. **Chronic Phytotoxicity**: These effects develop slowly over time and may not be immediately noticeable. Symptoms include stunted growth, delayed flowering, increased fruit drop, reduced yield, and lower quality fruits.
3. **Residual Phytotoxicity**: Some pesticides remain in the soil after application, particularly when sprayed directly on the ground. These residues can accumulate and affect root development, leading to symptoms similar to chronic phytotoxicity.
**Remedial Measures**
When phytotoxicity occurs, prompt action is necessary to minimize damage. Here are some effective strategies:
1. **Water Washing**: If detected early, rinse the affected plants with water to remove pesticide residue from leaves and branches. This helps reduce the concentration of harmful substances in the plant.
2. **Neutralization Treatments**: For leaf damage caused by phytotoxicity, applying a solution of sodium humate at 3000 times dilution can help. Alternatively, using a 5000 times diluted solution for irrigation may also be beneficial. For cases involving organophosphates or pyrethroids, spraying a 0.5% to 1% solution of lime water or soapy water can neutralize the effects and promote recovery.
3. **Top-Dressing**: After pesticide damage, applying fertilizers can help restore the tree's health and encourage new growth.
4. **Soil Cultivation**: Loosening the soil and adding phosphorus and potassium fertilizers can improve root development and support the tree’s recovery.
5. **Pruning**: Removing dead or damaged parts of the tree helps prevent further spread of damage and reduces the risk of disease.
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