Since February, the information about the phenomenon of wheat seedling yellowing, drying and dying in the wheat field has frequently appeared in the newspapers.

1. Internal cause refers to the ability of wheat plants to resist cold and drought damage. If wheat varieties with poor cold resistance are used for cultivation, the phenomenon of dead seedlings will easily occur in case of freezing injury. The cold tolerance of individual wheat seedlings sowed too early and whose panicles differentiated into two ridges before winter was weak, and the seedlings often died seriously in case of frost damage. In addition, some late sowing weak seedlings are prone to die in case of cold and drought damage due to less sugar accumulated by themselves.

2. External factors refer to various factors other than the wheat plant itself, such as adverse climate, soil conditions and inappropriate cultivation measures. For example, less precipitation in summer and autumn, insufficient soil moisture, less rain, snow and more cold wind in winter and spring will aggravate soil drought, make wheat tillering nodes in the soil layer with sudden changes in temperature and cold, and lead to wheat physiological dehydration and death.

For another example, if the varieties with weak winterness and shallow tillering nodes are selected, the seedlings will also die when the temperature difference is large due to the influence of soil temperature. In addition, if the seeds are sown too late, too deep or too dense, it is easy to form weak seedlings, which is not conducive to the safe overwintering of wheat. Especially if the soil moisture is insufficient, the winter water is not poured, which is more likely to cause the death of seedlings due to the combination of cold and drought.

There are three symptoms of wheat seedlings that have died:

1. The whole wheat is dry and yellow, but the root system is normal.

2. The overall growth of wheat seedlings in the field is not vigorous, and the phenomenon of withering and yellowing takes place in irregular flakes. It is difficult to see the presence of green leaves in the seriously withered and yellowing areas.

3. The leaf tip or leaf withers in the form of water loss, but the overall symptoms of withering and yellowing are mild.

Wheat withers and yellows in large areas. Who is the culprit?

Improper planting

For example, in the south area of Huanghuai winter wheat, the wheat sown before and after the cold dew (October 8), due to the high temperature, has different degrees of exuberance. Due to the failure of timely suppression or drug control of wheat fields, it is easy to cause large areas of frost damage when the temperature drops suddenly. Under the influence of higher temperature, some wheat fields with sufficient water and fertilizer are also the “worst affected areas” of flourishing seedlings. Wangchang wheat entered the jointing stage in advance before dormancy in winter. After suffering from frost damage, it can only rely on tillering to re-form tillering seedlings, which has buried a greater risk of yield reduction for the next year’s wheat yield. Therefore, when farmers plant wheat, they can refer to the practices of previous years, but also refer to the local climate and the field fertility and water conditions of that year to determine the amount and time of wheat planting, rather than rushing to plant with the wind.

Straw returning to the field is not scientific

According to the survey, the yellowing phenomenon of wheat in corn stubble and soybean stubble is relatively serious. This is because the wheat root is suspended and the root is attached to the soil poorly, resulting in weak seedlings. When the temperature drops suddenly (more than 10 ℃), it will aggravate the frost damage of wheat seedlings. However, the wheat fields with relatively clean straw in the field, the wheat fields that have been suppressed after sowing and the wheat fields with non-straw returning nature have almost no withering and yellowing except for the factors of flourishing.

Sensitivity of varieties to temperature changes

It is undeniable that the degree of cold tolerance of wheat varieties is different. Due to the continuous years of warm winter, everyone pays more attention to the late spring cold in March and April. The growers ignore the management of winter cold damage of wheat, especially the short stem and big spike as the only standard for seed selection, but ignore other factors. Since the sowing of wheat, it has been in a relatively dry state, and the superposition of adverse factors such as straw returning to the field and sudden drop in temperature has aggravated the occurrence of wheat seedling frost damage, especially for some wheat varieties that are not cold tolerant.

How to alleviate the large area of withered wheat seedlings?

At present, wheat seedlings are in hibernation, so it is of little significance to take remedial measures such as spraying and fertilizing, but in areas with conditions, winter irrigation can be carried out in sunny weather. When the temperature rises after the Spring Festival and the wheat enters the green returning period, 8-15 kg of nitrogen fertilizer can be applied per mu. After the new leaves grow out, humic acid or seaweed fertilizer+amino oligosaccharide can be used for leaf spray, which has a very good auxiliary effect on the recovery of wheat growth. To sum up, the phenomenon of large area withering and yellowing of wheat seedlings is caused by various factors such as climate, straw and unsuitable sowing time.

Cultivation measures to reduce dead seedlings

1. The selection of cold-resistant varieties and the selection of varieties with strong winterness and good cold-resistance are effective measures to prevent dead seedlings from freezing injury. When introducing varieties, all regions should first understand the adaptability of the varieties, take into account their yield and cold resistance, and the selected varieties can survive the winter safely at least in most local years.

2. Seedling irrigation For early sowing wheat fields with insufficient soil moisture, water can be used at the tillering stage. If the soil fertility is insufficient, a small amount of chemical fertilizer can be appropriately applied to promote early emergence of seedlings, so as to facilitate the safe overwintering of seedlings. The management of late-sowing wheat fields should focus on improving the soil temperature and preserving the moisture. The soil can be loosened by middle tillage. It is not suitable to water at the seedling stage, otherwise it will reduce the soil temperature and affect the upgrading and transformation of the seedling situation.

3. Timely winter irrigation and winter irrigation can form a good soil water environment, regulate soil nutrients in the topsoil, improve soil heat capacity, promote plant rooting and tillering, and produce strong seedlings. Watering in winter is not only conducive to overwintering and seedling protection, but also reduces the adverse effects of early spring cold damage, drought damage and drastic temperature changes. It is an important measure to prevent wheat seedling death in winter and spring.

The winter water shall be poured at the appropriate time. It is appropriate to freeze at night and dissipate in the day, and the temperature is 4 ℃. When the temperature is lower than 4 ℃, the winter irrigation is prone to freeze damage. Winter irrigation should be flexibly controlled according to soil quality, seedling condition and moisture content. The clay soil should be poured properly and early to avoid frost because the water cannot completely seep down before freezing. The sandy land should be watered late, and some of the wet land, rice stubble land or wheat fields with good soil moisture may not be watered, but the wheat fields with large amount of straw returned to the field must be watered in winter to crush the soil mass and freeze the pests.

4. Timely compaction can break the soil mass, compact the cracks, and stabilize the soil, so that the wheat root and soil can be tightly combined, and promote the root development. In addition, the suppression also has the function of raising and preserving moisture.

5. Properly covering with sand and wheat in winter can deepen the penetration depth of tillering nodes and protect the leaves near the ground, reduce soil moisture evaporation, improve the water condition at tillering nodes, and play a role of heat preservation and frost protection. Generally, covering with soil 1-2 cm thick can play a good effect of frost protection and seedling protection. The ridge of the wheat field covered with soil shall be cleared in time in spring, and the soil shall be cleared out of the ridge when the temperature reaches 5 ℃.

For varieties with poor cold resistance, wheat fields with shallow sowing and poor moisture content should be covered with soil as soon as possible. During overwintering, plastic film mulching can increase temperature and moisture, effectively prevent frost damage, promote plant growth, increase plant tiller and promote its development into large tillers, and improve the rate of tiller and ear formation. The appropriate time for film covering is when the temperature drops to 3 ℃. It is easy to grow in vain if the film is covered early, and the leaves are easy to freeze if the film is covered late. The late sowing wheat can be covered with film immediately after sowing.

However, it is worth noting that it is strictly forbidden to spray herbicides on wheat fields with severe frost damage. As for whether to spray herbicides normally after the Spring Festival, everything depends on the recovery of wheat seedlings. Blind spraying of herbicides on wheat fields is not only easy to cause herbicide damage, but also seriously affect the normal recovery of wheat seedlings.