Chestnut powdery mildew is caused by the fungus *Aspergillus subsplenium* and belongs to a group of species, but the primary pathogens affecting chestnuts are two specific types: *Pulmonaria* and *powdery powder*. The first type, known as chestnut powdery mildew, infects the underside of leaves. Its closed cystic structure has a diameter ranging from 214 to 250 μm, features needle-like filaments, and contains 2 to 4 ascospores. The second type, also called powdery mildew, attacks the upper surface of the leaves, with a smaller capsule diameter between 84 and 168 μm and bifurcated filaments. This disease is widespread and often severe, particularly in chestnut-growing regions. It primarily affects seedlings and young shoots, causing yellowing, curling, and drying of leaves, and can even lead to the death of young plants. In addition to chestnuts, it also harms other forestry crops such as tussock and ridges.
Symptoms of infection typically appear on leaves, shoots, and buds. Infected leaves develop yellow spots followed by a thick layer of white powdery growth. On dry, sunny days, the white spores become airborne, leading to distorted and deformed leaves. Young shoots infected by the pathogen also show white powdery deposits, which interfere with lignification and cause severe deformation.
The disease cycle begins when the pathogen overwinters in the tips of infected leaves within closed capsules. In April or May of the following year, ascospores are released and infect new shoots. Throughout the growing season, conidia continue to form as long as new growth occurs. The disease thrives in warm, dry weather, while rainy periods slow its spread. Seedlings and young trees are most severely affected, while trees over ten years old tend to be less impacted.
Control measures include winter sanitation practices, such as removing diseased leaves and pruning heavily infected branches, which should then be burned. A 3–5° lime sulfur solution can be sprayed on trees to eliminate overwintering pathogens and reduce the inoculum for the next season. Before spring growth begins, applying a 200-fold Bordeaux mixture can help prevent infection.
Infected plant parts should be removed early in the morning before dew dries, to avoid spreading spores. Diseased areas should be cut back below six buds and destroyed by burning. For chemical control, once symptoms appear, apply 600–800 times diluted 20% triadimefon EC or 25% wettable powder every 10 days, or use 200 times diluted 4% agricultural anti-120 powder.
In addition, similar powdery mildew diseases affect various fruit trees like apple, hawthorn, peach, plum, grape, citrus, walnut, mango, and lychee. Although not caused by the same pathogen as chestnut powdery mildew, these diseases share similar characteristics, including timing, location of damage, and symptoms. Therefore, they can be managed using similar control strategies.
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