Causes of crop injury and its symptoms

Although the causes of phytotoxicity are complex, they can generally be summarized into three main categories: First, incorrect use of pesticides or the presence of impurities in them. Second, the use of degraded or contaminated pesticides containing harmful substances. Third, a lack of understanding in the proper application techniques, such as spraying at inappropriate growth stages, unfavorable weather conditions, or using improper methods. The main symptoms of phytotoxicity include: 1. **Spot Type**: This type typically appears on leaves, stems, or fruit surfaces. Common manifestations include brown spots, mottled patterns, and net-like lesions. For example, irregular browning on rice leaves may occur if butachlor is misapplied early in the growing season. Similarly, Jinggangmycin can cause yellow spots on watermelon leaves, while Bordeaux mixture may lead to brown net-like spots on apple skin. 2. **Yellowing Type**: This symptom often affects leaves and stems, causing chlorosis due to interference with chlorophyll function. The yellowing can range from localized to entire plant discoloration. For instance, fenthion may cause yellowing on new shoots of watermelon, while simazine can lead to yellowing starting from the leaf edges and spreading across the whole plant. 3. **Deformation Type**: This includes curling, twisting, or swelling of leaves, stems, or roots. For example, dimethyltetrachlorobenzene can cause swelling in wheat seedlings, while herbicidal ether may result in blister-like damage on cotton leaves. 4. **Withering Type**: This occurs when the entire plant shows signs of wilting and death, usually due to herbicide misuse. Glyphosate, for instance, can cause yellowing and eventual death of rice seedlings, while chlorotoluron can lead to wilting and death in watermelon plants. 5. **Growth Stagnation Type**: This involves slowed or arrested plant growth. Improper use of green mellon in rapeseed can lead to reduced branching and lower yields, while paclobutrazol may delay heading in paddy fields. 6. **Sterility Type**: This occurs when reproductive structures are affected, leading to infertility. For example, rice shoot green can cause male sterility in rice, resulting in empty panicles and reduced yield. 7. **Drop Type**: This is commonly seen in fruit trees and broadleaf crops, with symptoms like leaf or flower drop. Copper preparations can cause defoliation in peach trees, while ethephon misuse may lead to fruit drop in hawthorns. 8. **Fruit Quality Decline**: This involves smaller or malformed fruits, poor surface appearance, and reduced quality. Ethylene toxicity in watermelons can cause dark red, odoriferous fruits, while copper-based sprays may lead to brown spots on tomato skins. **How is Phytotoxicity Different from Disease?** Phytotoxicity often presents irregularly across a field, while diseases tend to spread uniformly. Spot-type phytotoxicity has variable lesion shapes, whereas fungal diseases usually have a central point of infection with consistent patterns. Yellowing from phytotoxicity tends to develop quickly under sunny conditions, while nutrient deficiencies cause slow, uniform yellowing. Virus-induced yellowing often shows broken green patterns and systemic symptoms, unlike chemical-induced yellowing. Deformities caused by chemicals appear locally, while viral diseases affect the whole plant systemically. Wilt from phytotoxicity lacks a clear center and progresses slowly, while disease-related wilt is often rapid and accompanied by root discoloration. Growth delays from chemicals are usually accompanied by other symptoms, while physiological issues show root problems and uniform yellowing. In summary, phytotoxicity typically shows specific symptoms without a pathogen, while diseases involve pathogens and may present systemic effects. To prevent phytotoxicity, it's essential to conduct small-scale trials before large-area applications, strictly follow pesticide instructions, and ensure proper equipment cleaning. After injury, regular crop monitoring and remedial actions such as fertilization, irrigation, and hormone application can help reduce damage.

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