Wheat is the main food crop planted by farmers. In recent years, the yellowing of wheat leaves has occurred to varying degrees almost every year, which seriously affects the yield of wheat. In order to ensure a bumper harvest of wheat in this area, the reasons for the yellowing of wheat leaves and preventive measures are as follows for your reference.
1. Causes of yellowing of wheat leaves
1.1 Poor management or bad external environmental conditions
The overall planting density of wheat is too large, causing the wheat population to be too large, affecting photosynthesis of wheat, and insufficient nutrient supply, resulting in yellowing of leaves. In addition, wheat encounters cold and cold, and is also prone to freezing damage. After freezing, the wheat is yellowed in the lower leaves, and the disease resistance of wheat is reduced.
1.2 Fertilization is unreasonable
Insufficient base fertilizer, especially when the nitrogen fertilizer is insufficient, the wheat seedlings are small and yellow. Lack of certain nutrients will also seriously hinder the growth and development of wheat and produce yellow seedlings. Wheat seedlings are more common in yellowing. First, the nitrogen deficiency type is yellow. The nitrogen-deficient plants in wheat are short and weak, and the tillers are few and weak. The leaves of the seedlings are yellow and the leaves are withered, and the old leaves in the lower leaves are yellow and dry. The second is the lack of phosphorus and yellowing. Wheat is deficient in phosphorus, with few secondary roots, less tiller, darker green leaves, yellow tip leaves, blue-green leaves, and purple-leaf leaves. If not remedied in time, it will result in less spikes, less grain, and 1000-grain weight. The third is the lack of potassium and yellowing. The wheat seedlings lacking potassium and yellowing often start from the tip of the old leaves and then extend down the veins. The macula is partially visible and has a mosaic yellowing. Under the yellow leaves, the late stage is attached, the stems of the diseased seedlings are small and thin, prone to premature aging and lodging. The fourth is the lack of calcium and yellowing. Calcium deficiency is mainly manifested in the new leaves, the upper leaves are obviously reduced, the veins are yellowed, the leaves grow at the leaves, the leaves are dead, the tips of the leaves are often bent, the young leaves can not be unfolded, and the leaves are yellow. The fifth is iron deficiency type yellowing. Iron deficiency is mainly manifested in the new leaves, but the top buds do not die. It is characterized by yellowing of the new leaf mesophyll tissue. Or the long-term extreme iron deficiency, the upper leaves can all turn yellow and white, the tip and leaf edge will gradually wither and expand inward. Sixth, the magnesium deficiency type is yellow. When the wheat is deficient in magnesium, the leaf margin tissue of the middle and lower leaves gradually loses green and yellow, the veins are still green, the leaf edges curl upwards or downwards, and the leaves often wither.
1.3 phytotoxicity
The drugs that cause wheat seedling poisoning are mainly herbicides . Herbicides are applied strictly, and may cause phytotoxicity if they are slightly inadvertent, and herbicides used for broadleaf weeds cannot be used in wheat fields. Once the phytotoxicity is caused by the herbicide, there is no effective way to rescue the dead wheat seedlings.
2, preventive measures
2.1 Strengthen management
If the bottom fertilizer is sufficient, the water has been poured after the Spring Festival, and the field is not too dry. It should be dominated by ploughing and ploughing to promote the growth of wheat seedlings. If the bottom fertilizer is insufficient, the water will not be poured after the Spring Festival, and the drought in the field is serious, and management should be strengthened in time. Before applying water, apply fertilizer, mainly with quick-acting fertilizers such as ammonium bicarbonate and ammonium sulfate. Urea is slow to be converted at low temperature and should not be used. Appropriate application of potassium fertilizer to promote the growth of wheat seedlings. Wheat seedlings often yellow due to the damage of mites and rust. The monitoring and reporting of pests and diseases should be strengthened, and the appropriate symptomatic treatment should be applied. While controlling aphids and red spiders, add appropriate amount of anti-disease fungicides , such as triadimefon, carbendazim, and propiconazole. For wheat with severe yellowing of leaves, the wheat regulator McDonald's can be used once to promote wheat rooting, shorten internodes, enhance disease resistance, and prevent lodging.
2.2 deficiency of fertilizer
The first is the prevention of nitrogen deficiency. The reason for the yellowing of wheat is generally due to the early sowing, the sandy field, the lack of base fertilizer, and the fertilizer is not timely, and the amount of fertilizer is small, and the yellowing of wheat is most likely to occur. The remedy is: if the wheat seedling stage is deficient in nitrogen, the urea can be applied 150~225 kg/hm2, and the nitrogen deficiency and yellowing after the spring. The urea can be applied at a rate of about 75 kg/hm2 during the regreening period, and the urea is applied at a height of 180 to 225 kg/hm2 during the jointing or jointing period. It can also be sprayed on the foliar when the wheat is yellow, and sprayed with 2% urea solution twice, each time about 7 days. The second is the prevention of potassium deficiency. Wheat seedlings lack phosphorus, can be applied to calcium phosphate 675 ~ 750 kg / hm2, can also be sprayed with foliar application, spray 3% calcium perphosphate aqueous solution 900 kg / hm2, spray 1 to 10 d interval, even spray 2 to 3 times. The third is the prevention of potassium deficiency. Potassium deficiency wheat field, in the wheat seedling stage, the application of potassium chloride or potassium sulfate 112.5 ~ 150.0 kg / hm2, can also apply plant wood ash 450 ~ 750 kg / hm2; in the middle and late growth period of wheat, foliar application of 10% grass ash leaching solution , or 0.2% ~ 0.3% potassium dihydrogen phosphate aqueous solution 900 kg / hm2, even spray 2 to 3 times, interval 7 ~ 10 d, the control effect is very significant. The fourth is calcium deficiency prevention. In the absence of calcium, 0.3% calcium chloride solution or 1% calcium perphosphate leaching solution can be sprayed on the foliar surface, sprayed once every 7 to 10 days, and even sprayed 2 to 3 times, the effect is remarkable. The fifth is iron deficiency prevention. In the case of iron deficiency, the surface of the wheat seedlings can be sprayed with 0.2% ferrous sulfate, sprayed once every 7 to 10 days, and even sprayed 2 to 3 times to relieve the symptoms. Sixth is the prevention of magnesium deficiency. In the case of wheat deficiency of potassium, foliar application can be carried out with a 0.3% aqueous solution of magnesium sulfate. In addition, the soil is too acid to cause the roots to become black, so that the ability to absorb water and fertilizer is reduced, the wheat seedlings are yellowed because they do not get enough nutrients, and 750 to 1 050 kg/hm2 of quicklime or 750 to 1,500 kg/hm2 of grass ash can be applied. To neutralize the acidity of the soil, restore the normal growth of the wheat seedlings.
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