First, symptoms and causes
The disease typically appears during the near-mature stage of the fruit. At the early stage, brownish crescent-shaped or spot-like lesions appear near the lenticels. As the disease progresses, the lesions grow slightly larger, their color deepens, and they become slightly sunken. Multiple lesions can occur on different parts of the fruit at the same time. On the surface of the pear, dark brown spots, irregular blocks, or textured lesions form, resembling scratch marks made by a chicken's claws. This is why farmers commonly refer to the condition as "Chicken Paw Disease" or "Chicken Claw Disease." In severe cases, multiple lesions may merge into nearly circular depressions surrounding the lenticels.
There are three main reasons for the formation of these lesions: an imbalance of calcium nutrients after bagging, thickening and cracking of the fruit peel due to lack of protection from the stratum corneum, and high enzyme activity. The microenvironment inside the fruit bag differs from that of an unbagged fruit, leading to reduced calcium levels. This combination increases the risk of pericarp cracking and weakens the protective layer, triggering enzymatic reactions that cause browning. A dense tissue structure (lesions) forms as a protective mechanism, which can be seen as the pear’s natural immune response. Therefore, the lesions do not spread further or rot, but they do affect the fruit's market value.
Several factors influence the occurrence and spread of the disease, including the type of fruit bags used (such as paper bags, their color, transparency, and air permeability), excessive nitrogen fertilizer application, fruit swelling rate, climate conditions, and soil fertility.
Second, comprehensive prevention and control technology
1. Fertilization: Apply organic fertilizer and ensure balanced nutrition. In autumn, apply 3 to 5 cubic meters of organic fertilizer per acre. For deep soils, it's recommended to dig and mix the fertilizer into the soil. For sandy, clayey, or alkaline soils, trenching and soil fertilization should be used. In severe cases, 100 to 200 grams of sodium tetraborate (borax) can be applied before flowering. During the development period, if the tree shows signs of weakness, apply a nitrogen-phosphorus compound fertilizer in the early stages (no more than 3 kg per tree during the fruiting season).
2. Winter pruning and thinning: Prune branches properly during winter to ensure good ventilation and light penetration within the canopy. The number of fruits per acre should not exceed 14,000, and the yield should be controlled between 3,500 and 4,000 kg.
3. Calcium spray on young fruit: Before bagging, spray young fruit with calcium solutions such as calcium chloride or other organic calcium salts. Spray once every 7 to 10 days, and up to two or three times if necessary.
4. Bagging: Use fruit bags with good air and light permeability (with a light transmittance of about 10%), or choose bags coated with active materials on the inner layer. The optimal time for bagging is from late May to early June.
5. Watering: Ensure proper watering before flowering and after frost. In other periods, water according to the plant's needs, avoiding overwatering.
Additionally, multiple cultivators can help raise soil temperature, enhance root activity, and improve calcium absorption efficiency, thereby reducing the occurrence of the disease to some extent.
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