A Detailed Guide to Managing Wheat Seedlings Before Winter by Leaf Color

1. Causes of yellow leaves in wheat seedlings and their management. First, soil drought, which mostly occurs in wheat fields with insufficient subsoil moisture or where moisture escapes through cracks in the soil. Its characteristics are slow tiller emergence, grayish-green leaf color, short and small heart leaves, slow or stalled growth (known as "shriveled-heart seedlings"), gradual yellowing and drying of the middle and lower leaves, and few, thin roots. The key management point is to apply 15 kg of ammonium bicarbonate per mu along with irrigation. Second, nitrogen deficiency, in which seedlings are thin and weak and grow upright, tillering is reduced, leaves are narrow and short, and the lower leaves gradually turn yellow and dry starting from the leaf tips and progressing upward. The key management point is to apply 7-8 kg of urea per mu, or 20-25 kg of ammonium bicarbonate, or 600-700 kg of human and animal manure, applied in furrows between rows or diluted with water and poured on. Third, hard, compacted soil, in which a lack of moisture and air in the soil makes it difficult for roots to spread, causing wheat leaves to be yellow and short and tillers to fail to appear on time. The key management point is to irrigate promptly first, then deep-plow and loosen the soil to break up the hardened layer. Fourth, excessive seeding rate, in which crowded seedlings compete with each other for light, nutrients, and water, making the plants yellow, thin, and weak. The key management point is to first thin the seedlings promptly, especially the clumped seedlings at field edges, corners, and within the field, which must be thinned early and thoroughly, then apply a small amount of quick-acting nitrogen and phosphorus fertilizer along with irrigation to make up for the excessive consumption of soil nutrients and help the wheat seedlings shift from weak to strong. Fifth, insect pests; damage by wheat aphids or red spider mites can also cause wheat leaves to turn yellow. The key management point is to promptly spray with a 1500-2000 times dilution of 40% omethoate emulsifiable concentrate when damage is found.

2. Causes of red leaves in wheat seedlings and their management. First, waterlogging, which occurs when there is excessive autumn rain or the wheat field is low-lying, causing leaves to turn dark red and, in severe cases, root rot and dead seedlings. The key management point is to promptly open ditches for drainage and apply a small amount of quick-acting fertilizer to promote early seedling growth. Second, phosphorus deficiency, in which wheat seedlings have poor root development, dark green and lusterless leaves, purplish-red leaf tips and leaf sheaths, thin and small plants, and reduced tillering or even no tillering. The key management point is to apply 20-30 kg of superphosphate per mu along with hoeing and loosening the soil. Third, salinity-alkalinity damage, which often produces patches of purplish-red stunted old seedlings, and in severe cases causes patchy death of seedlings. The key management point is to promptly hoe to raise temperature and break up surface crusting, inhibit salt return, and apply winter fertilizer at the right time to promote tillering and strong seedlings; in the following spring at the green-up stage, combine topdressing with irrigation to leach salts. Fourth, freezing damage; when the temperature suddenly drops below 0°C, wheat seedlings may be damaged by cold and their leaves turn red. The key management point is to apply 75-100 kg of plant ash per mu along with hoeing and mounding soil around the roots, and if necessary, after wheat enters the overwintering period, spread a layer of warm ditch manure along the rows to protect the seedlings through the winter safely.

3. Causes of purple leaves in wheat seedlings and their management. When wheat seedlings are deficient in boron, stems and leaves become thick and curved, and leaves turn purple, forming purple-leaf seedlings; in severe cases, the later spikes do not fill properly, affecting yield. The key management point is to use 150-200 g of borax per mu, applied with an appropriate amount of nitrogen and phosphorus fertilizer diluted in water, or use 50-100 g of borax per mu diluted in 50-60 kg of water for foliar spraying.

4. Causes of brown leaves in wheat seedlings and their management. When wheat seedlings are deficient in potassium, growth is slow, root development is poor and roots rot easily, leaves are dark green or blue-green and droop weakly, leaf tips and margins turn yellow and dry, then turn brown, forming brown-leaf seedlings. The key management point is to apply 15 kg of potassium sulfate or 100 kg of plant ash per mu in furrows opened between rows, or spray the leaves with a 0.2%-0.3% potassium dihydrogen phosphate solution.

5. Causes of yellow-white leaves in wheat seedlings and their management. When wheat seedlings are deficient in zinc, little-leaf disease occurs, leaf margins twist and crinkle, the areas along both sides of the veins turn from green to yellow and even white, and yellow, white, and green striped bands appear along the margins, forming yellow-white seedlings. The key management point is to use 1 kg of zinc sulfate per mu mixed with 15-20 kg of fine dry soil or organic fertilizer and apply it in furrows between rows; the earlier the effect, the better, or spray the leaves with a 0.1%-0.2% zinc sulfate solution.