How to prevent and control onion neck rot? Understanding the disease development pattern is key

1. Symptoms and characteristics: It mostly occurs during the maturity or storage period of onion bulbs. Besides onions, it can also infect other allium vegetables. If infected during the growing period, light brown lesions mainly appear on the leaf sheaths and the neck of the bulb, the internal tissue rots, and gray mold appears under humid conditions. If infected during storage, dry, slightly sunken lesions appear on the top and shoulders of the bulb, becoming soft and light brown, with gray mold between the scales. Later, small dark brown sclerotia form.

2. Disease development pattern: The pathogen of this disease is Botrytis allii. The pathogen overwinters as mycelium and sclerotia with diseased plant residues in the field, or with onion bulbs in storage sites. Conidia spread with airflow and invade through plant wounds. Low temperature and high humidity both favor disease development. Rain during harvest, bulb skins not yet dry, and high humidity in storage areas all make the disease more likely. 3. Control methods: (1) Choose disease-resistant varieties and practice crop rotation with other vegetable types; (2) Apply supplementary fertilizer at the right time, avoid applying too much or too late, and the organic fertilizer added must be fully decomposed; do not apply excessive nitrogen fertilizer; (3) Water scientifically. Do not use flood irrigation when watering, and pay attention to drainage after rain; (4) Harvest after onions are fully mature, carefully cut off the top of freshly harvested bulbs, dry them thoroughly in the sun, and then store them; (5) When bulbs are freshly harvested, irradiate them with infrared light for 6 minutes (the lamp about 15 cm from the onions), which can reduce rot during storage; (6) For chemical control, during the growing period spray 50% procymidone wettable powder at 600 times dilution, or 40% carbendazim suspension concentrate at 800 times dilution, or 70% thiophanate-methyl wettable powder at 1000 times dilution, generally once every 7~10 days, for 2~4 consecutive sprays.