What are the most common pests and diseases that affect Zhangqiu onions, and how can they be prevented? During the growth period of green onions, several diseases and pests commonly occur. The main diseases include frost damage and purple spot disease, while the primary pests are onion thrips, onion leaf miners, and onion flies.
Onion downy mildew is a serious fungal disease that causes distorted, pale green leaves with a wet appearance. A white mold may appear on the surface of the leaves and stems, especially when the plant is damp. When dry, white spots develop on the leaves. Lesions on the leaves are usually oval or elongated, varying in size, with a yellowish-green color and unclear edges. In wet conditions, these lesions produce white mold, while in dry weather, they turn into dark spots. If the lower part of the leaf is infected, the upper portion often droops.
Another common disease is onion brown spot, which mainly affects the leaves and flower stalks. The lesions typically start from the tip of the leaf or the middle of the flower stalk and spread downward within a few days. Initially, the lesions are small, slightly sunken, and purple-brown in color. Under high temperatures, the affected areas become covered with brown to black powdery mildew arranged in concentric rings. As the disease progresses, the lesions grow larger and merge, eventually causing the leaves and flowers to die.
To manage these fungal diseases, infected plants should be treated immediately with protective sprays. You can alternate between the following fungicides: 75% chlorothalonil diluted at 600–800 times, 40% carbendazim at 500–600 times, 50% thiophanate at 500 times, and 40% diethylaluminophosphate at 400 times. Apply the spray every 3–5 days, possibly repeating it 2–3 times. For downy mildew, you can also use 25% Ruipo Cream diluted at 1000 times.
For pest control, onion thrips and leaf miners can be managed by spraying 40% dimethoate emulsion at 800–1000 times or 50% dichlorvos EC at 1000 times. To prevent thrips, you can also use 50% phoxim at 1500 times. Onion flies, also known as onion maggots, lay eggs that hatch into larvae which feed inside the bulb, causing rot, yellowing, and even plant death. To control them, spray 50% dichlorvos EC at 1000 times during adult emergence. During the larval stage, apply 50% phoxim at 2000 times or 40% dimethoate at 1000 times directly to the roots.
Proper crop rotation, good field drainage, and regular monitoring are essential for long-term prevention. Keeping the growing area clean and free of debris can also reduce the risk of disease and pest infestations. By combining cultural practices with timely chemical treatments, farmers can effectively protect their Zhangqiu onions and ensure a healthy harvest.
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