Chestnut powdery mildew is caused by the fungus *Aspergillus subsplenium* and belongs to a group of related species. However, the primary pathogens responsible for damage are two specific types: *Erysiphe cichoracearum* (commonly known as chestnut powdery mildew) and *Podosphaera leucotricha*. The former infects the underside of leaves and is referred to as powdery mildew. Its closed cystic structures have a diameter ranging from 214 to 250 micrometers, with needle-like appendages containing 2 to 4 ascospores. The latter infects the upper surface of leaves and is also called powdery mildew. Its closed capsular structures measure between 84 to 168 micrometers, with bifurcated filaments attached. This disease is widely distributed and frequently occurs in chestnut-growing regions. It mainly affects seedlings and young shoots, causing yellowing, curling, and drying of leaves, and in severe cases, can lead to the death of young plants. In addition to chestnuts, it also affects other forest crops such as tussock and ridge plants.
Symptoms of infection include yellow spots on leaves followed by a white, powdery coating. When the weather is dry, the white spores become airborne, leading to distorted and deformed leaves. Infected young shoots also develop a white coating, which hinders lignification and causes severe deformation.
The disease cycle begins when the pathogen overwinters in infected leaf tips within closed fruiting bodies. In April or May of the following year, ascospores are released to infect new shoots. Throughout the growing season, conidia continue to form as long as new growth appears. Warm, sunny, and dry conditions favor spore spread and disease development, while wet and rainy weather slows it down. Seedlings and young trees are most severely affected, whereas trees over ten years old show milder symptoms.
Control measures include winter sanitation to remove infected leaves, pruning of severely damaged branches, and burning them. A 3-5 degree lime sulfur solution should be sprayed on the tree to eliminate overwintering pathogens and reduce the inoculum for the next season. Before bud break in spring, applying a 200-fold Bordeaux mixture can help prevent infection.
Infected parts should be removed early in the morning when dew is still present, making it harder for spores to spread. Diseased areas should be cut below six buds and destroyed immediately to prevent further transmission.
Fungicides should be applied at the first sign of infection. Options include 600–800 times diluted 20% triadimefon emulsion or 25% powder, applied every 10 days. Alternatively, a 200-fold dilution of 4% agricultural anti-120 powder can be used.
Additionally, similar powdery mildew diseases affect various fruit trees such as apple, hawthorn, peach, plum, grape, citrus, walnut, mango, and lychee. Although these are caused by different pathogens, they share similar characteristics—white powdery coatings, similar timing of occurrence, and comparable symptoms. Therefore, the control methods used for chestnut powdery mildew can also be effective for managing these related diseases.
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