How to manage onions during the bulb swelling stage? Sharing the latest technical key points
When planting onions, the bulb swelling stage is the critical period, the key period that determines yield and quality. Onions generally grow in the middle soil layer, and at this time a series of management tasks must be done well, including water control, nutrition, preventing bolting, and preventing pests and diseases. They need more meticulous care than other growth stages. The key management points after entering the bulb swelling stage will be revealed one by one for everyone right away.
1. Water control
The onion bulb swelling stage occurs right during the summer solstice period, when the outside temperature is high, the daily light exposure time is long, and water evaporates very quickly. At the same time, the bulb keeps swelling continuously. If the bulb lacks water, it will stop growing, and if the aboveground leaves lack water, they will lodge and not recover. Therefore, the number of irrigations and the irrigation amount need to be gradually increased. Generally, water once in the morning and once in the evening each day, and irrigate once at an interval of one week. In dry weather, the interval can be shortened and watering can be done freely, but in all cases the soil must be watered thoroughly to keep the surface layer moist. When it is close to maturity, stop watering; the outer skin will grow and become fixed, and watering again will cause the skin to split.
2. Nutrition
Before entering the bulb swelling stage, apply a topdressing once, using a compound fertilizer with long-lasting fertilizer effect to maintain the needs of the bulb during the swelling stage. In the middle of the swelling stage, fertilizer can be applied outside the roots by spraying trace element fertilizer to prevent the leaves from yellowing due to deficiency symptoms. In the late swelling stage, apply a topdressing once to promote maturity, but nitrogen fertilizer can be applied less, and mainly more phosphorus and potassium fertilizer should be applied. This is because onions are mainly harvested for their bulbs, and phosphorus and potassium fertilizers mainly help bulb growth. Too much nitrogen fertilizer easily causes excessive vegetative growth, excessive leaf growth, and leaves that grow too tall are prone to lodging, reducing photosynthesis.
3. Preventing bolting
Onions are mainly harvested for their bulbs, and the quality of the bulbs needs to be maintained. Therefore, if early bolting is found in the field, it must be cut off immediately to avoid consuming nutrients through bolting and causing the bulb to become hollow, which would make it useless. Moreover, if bolting consumes nutrients, the bulb cannot swell and growth stops. Generally, attention should be paid to temperature management, as a sudden low temperature easily induces early bolting.
4. Pest and disease control
In summer, onions are most prone to onion flies and downy mildew. Onion flies, also called root maggots, mainly bore into and feed on the bulbs and can also cause the leaves to rot and wither, so they must be controlled as a priority. Generally, 40% phoxim can be used for root drenching to prevent and treat them. Downy mildew mainly harms the aboveground leaves; the diseased parts turn yellow and rot, and a large amount of white mold grows. It occurs severely when humidity is high, so during the swelling stage, 70% chlorothalonil at 600 times dilution can be used for spraying. Root drenching at an interval of about one week, twice in succession is about enough. Pesticide spraying at an interval of three days is fine, and three times in succession can bring it under control.
The swelling stage is a critical period, and it is also a fragile period that requires special care. The above are the tasks to be done during the onion swelling stage, and not one of them can be neglected. Only in this way can the swelling stage be passed safely and the desired yield and better quality be obtained.