Rice Seedling Root Coiling During the Transplanting Season: Management Techniques and Control of Bacterial Wilt and Damping-Off

Rice is a species of the grass genus Oryza, and also the most important and longest-cultivated grain species in the genus Oryza. Now that the transplanting season is approaching, how can rice seedlings coil their roots well? What are the management techniques? How do you prevent and control bacterial wilt and damping-off?

It's transplanting season again. How can rice seedlings coil their roots well?

1. Fill with an appropriate amount of mud and sweep the tray surface clean. The mud slurry must not be too thick; after filling the tray with slurry, sweep it level and even with a bamboo broom and sweep away excess slurry, then after sowing gently press the seeds down with a soft broom. If raising seedlings with dry fine soil, first fill half the cell depth with fine soil, sweep away the excess fine soil with a bamboo broom, cover with a layer of fine soil after sowing, then sweep the soil off the tray surface and water thoroughly.

2. Water management in the seedling field should follow the principle of wet first, dry later. From sowing to emergence, keep the tray soil sufficiently moist to maintain moisture for emergence; after the three-leaf-one-heart stage, drain the water from the seedling trenches and focus on dry raising. Only when seedlings lose water and their leaves curl during long spells of hot, dry sunny weather, when removing the film for early rice seedling raising, or when a low-temperature cold wave hits, is it necessary to irrigate with running water or briefly flood to protect the seedlings; generally no water layer is established on the tray surface.

3. Transplant in a timely manner. When the seedlings reach a leaf age of 3.5 leaves and a seedling height of 10cm, they can be transplanted in a timely manner on a clear, fine day.

Seedlings from water-raised rice (water-grown root system). The root system has few roots and few root tips, and the roots suffer severe transplanting injury, so the seedlings turn green slowly and take a long time to turn green.

Seedlings from moist-raised rice (moist-grown root system). Compared with water-raised seedlings, the root system is more numerous, with sparse fibrous roots and root hairs at the root tips; the seedlings take less time to turn green, the tillering stage comes earlier, and the number of tillers increases.

Seedlings from dry-raised rice (dry-grown root system). Many fibrous roots, many root hairs, many root tips, and a well-developed root system, with markedly enhanced water and fertilizer uptake capacity; the seedlings turn green quickly, tiller early, and the number of effective tillers increases noticeably.

Seedlings from pot-raised rice (dry-grown root system) have an even more developed dry-grown root system, and the seedlings undergo no reviving process after transplanting, making this one of the best ways to cultivate strong seedlings in current high-yield rice cultivation.

What are the management techniques for the rice seedling stage?

1. Temperature management: Before the seedlings stand upright, focus on keeping them warm, maintaining about 30°C inside the film to promote emergence. When the seedlings grow to the 1.5-2 leaf stage, pay attention to lowering the temperature to harden them, keeping the temperature inside the film at about 25°C; when it exceeds 25°C, open both ends for ventilation and cooling. When the seedlings reach the three-leaf stage, on sunny days uncover by day and cover by night to harden the seedlings well. Once the temperature stabilizes at about 10°C, the film can be removed to cultivate ideal seedlings.

2. Water management: On the basis of watering enough bottom water at sowing, generally no watering is needed before emergence; if water is found to be insufficient and parts of the bed surface are dry and turning white, water promptly. When the seedlings turn green, generally give one supplementary watering; at the one-leaf-one-heart stage, water in combination with ventilation and hardening; thereafter water as appropriate. After removing the film, replenish water promptly when it is lacking, and 5-7 days before transplanting, sun the bed to firm the seedlings.

3. Fertilizer management: Generally no fertilization is needed at the seedling stage; after the 2-3 leaf stage, fertilize according to growth conditions, spraying 0.2% monopotassium phosphate once. If fertilization is needed, 7-10 days before transplanting appropriately apply a send-off fertilizer of 5 kg of urea per mu, which not only increases the seedlings' cold resistance and speeds up greening but also promotes early tillering.

4. Weed control in the seedling bed: Base it mainly on manual weeding; it is strictly forbidden to use highly effective, highly toxic, high-residue herbicides for weeding. Pull weeds by hand in the field before transplanting.

How do you prevent and control bacterial wilt and damping-off in rice seedlings?

1. The causes of rice bacterial wilt include: excessively low temperature, excessively large temperature differences, alkaline soil, insufficient light, thin and weak seedlings, and too large a seeding rate, among other factors.

2. The main causes of rice damping-off are: low temperature, excessively large temperature differences, alkaline soil, insufficient light, thin and weak seedlings, and excessive density, among other factors.

3. Buy disinfectant fungicides for damping-off: Against the damping-off pathogens - Fusarium, Rhizoctonia, and molds - choose effective disinfectant fungicides, such as the conventional agents hymexazol, metalaxyl, thiram, azoxystrobin, and so on.

4. Because the pathogens invade through the seedling root system, you should also use root-promoting and growth-regulating agents, such as rooting powder, biological bacterial agents (Jundafu), brassinolide, Wukangwang, and so on. Just focus on the above two aspects, and choose agents from reputable manufacturers with sufficient content and good effects.

5. After applying the chemicals, you must pay attention to the following points to effectively control the disease and gradually relieve it.

(1) Avoid repeated applications

When seedlings get sick, farmers get anxious along with them; if one spray does not work, they spray again the next day and the day after, and the result is that the more they spray, the worse it gets, and the seedlings die faster. It is best to leave 5-7 days between two applications; continuous application will cause chemical poisoning, which is instead detrimental to controlling the disease. If chemical poisoning occurs, the symptoms can be relieved by spraying Jundafu + Wukangwang on the leaves.

(2) Switch chemicals for the second application

If damping-off does not respond 5-7 days after application, switch to a different chemical for the second application, to avoid using the same one twice and producing resistance that affects treatment.

(3) Avoid excessive humidity after application

After application, the disinfectant fungicides will kill the damping-off pathogens in the soil, but to control and relieve the disease, the most important thing is still to get the seedlings to grow new roots. While the rooting agent takes effect, you must also artificially create a dry-raising state for the rice seedlings, because “dryness grows roots”; therefore, if the seedling bed humidity cannot be brought down after spraying and you water frequently, it will be very hard for the seedlings to grow new roots, and the damping-off cannot be controlled.