Apple powdery mildew is a common fungal disease that primarily affects young apple tree shoots, leaves, buds, flowers, and developing fruits. This disease can significantly weaken the plant, reducing fruit yield and quality. The infection often starts on tender growth, causing stunted development and various visible symptoms on the foliage.
Symptoms of powdery mildew include the inhibition of new shoot growth, with shortened internodes and narrow or tightly curled leaves. These affected leaves become hard, brittle, and may develop a white, powdery coating that later turns brown. As the disease progresses, the white fungus spreads across both sides of the leaf. The upper surface of the leaf may show uneven coloration, while the underside develops distinct white spots. Affected leaves often appear distorted, with wavy edges and a shriveled appearance. In severe cases, the leaf tips or edges turn brown, and the entire leaf eventually dries up and falls off.
Infected buds take on a grayish-brown or dark brown color, becoming elongated and thin with loose scales. The bud’s outer layers may not close properly, leading to reduced viability. When these buds finally sprout in spring, their growth is slow and weak, making it difficult for them to develop into healthy shoots. Flower buds are also impacted—petals become pale green, thin, and elongated, while sepals and pedicels may be deformed. The reproductive structures lose their ability to pollinate and fertilize, ultimately leading to bud death. Severely infected buds may shrink and die prematurely.
On young fruits, the disease manifests as white patches near the stem, causing the affected areas to harden. As the fruit grows, the white powder disappears, leaving behind a network of rust-like spots. The hardened tissue may crack over time, further damaging the fruit. Additionally, the fruit stems may become shriveled, and the fruit surface may develop a cork-like texture.
To manage apple powdery mildew effectively, several control measures should be implemented:
1. **Dormant Season Pruning**: Remove infected buds and diseased parts during winter to reduce the initial source of infection.
2. **Fungicide Spraying During Growth Periods**: The most critical time for protection is in early spring. Apply 15% triadimefon (Triaden) at a dilution of 1000–1500 times, or 70% thiophanate-methyl (Thiophanate-Methyl) at 1000 times. For more resistant cases, alternatives such as Fuxing, Beclomethasone, or stronger fungicides may be used. Regular monitoring and timely application are essential to prevent the spread of the disease.
By combining cultural practices with proper chemical treatments, growers can significantly reduce the impact of powdery mildew on their apple trees. Early detection and consistent management are key to maintaining healthy orchards and high-quality fruit production.
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