In recent years, due to various reasons, the yellow leaf phenomenon of garlic frequently appears, leading to a decrease in the yield of garlic and a decrease in quality. Generally, the field yield is reduced by 10%-30%, and the field is particularly severe. Here are some of the reasons and prevention methods for garlic yellow leaves.
First, the causes and characteristics of garlic yellow leaves
1.1 physiological yellow leaves
1.1.1 Soil acidification. The acid soil hazard causes yellow leaves, and the neutral soil is suitable for the growth of garlic, which is most suitable for pH 7.0-7.4. When the application of organic fertilizer is less, a large amount of chemical fertilizer (complex fertilizer, superphosphate) will acidify the soil, causing the garlic leaves to grow slowly, weak, and the outer leaves are yellow.
1.1.2 Drought. In the production process of garlic, watering is not noticed, the soil is dry, and the water shortage of the plant is easy to cause yellow leaves, which is common in winter and spring when rainfall is low.
1.1.3 lack of trace elements. The calcium-deficient heart leaves are yellowed, the physiology is blocked, and the magnesium-deficient outer leaves are sharpened.
1.1.4 Toxic gas hazards. First, the application of ammonium bicarbonate will cause ammonia damage, so that the tip of the blade will wither and gradually turn brown. Second, the factory emits exhaust gas (CO), causing the damaged leaves to quickly lose green, the leaves begin to turn grayish white, and the leaves are yellow and diseased. There are no symptoms such as mildew.
1.1.5 Physiological de-fertilization. Occurs in the early stage of garlic growth. After 20 days of garlic emergence, the tip of the leaf began to lose green to brownish brown, and the tip of the leaf was yellowish. The field showed uniform incidence and no central disease. The reason is "returning mother", also called physiological de-fertilization. The nutrients stored in the garlic are used up, and the flower buds and garlic cloves begin to differentiate. If the fertilizer is not timely, the yellow leaf phenomenon will occur.
1.2 pathological yellow leaves
1.2.1 Garlic leaf blight. Symptoms: The main damage to the leaves, the disease mostly begins at the tip of the leaf or other parts of the leaf. It is initially white with small dots. When enlarged, it is irregular or elliptical grayish white or grayish brown lesions. When the leaves die. In Pengzhou City, the onset of the disease began in early November, and entered the peak incidence in March of the next year. The general disease rate was over 20%. The pathogen is Pleosporaherbarum (Pers.exFr.) Rabenk, which belongs to the fungi community.
1.2.2 Garlic leaf blight. Symptoms: The main damage to the leaves, the leaves at the beginning of the leaves in the middle of the leaves or the tip of the leaves pale pale yellow water-immersed spots, the edges are light green, the lesions spread quickly, the leaves are drooping, when the humidity is high, the sparse gray mold, disease The spot is dead. Most of the production is harmful in October and March, which is a common cause of garlic. The pathogen is Stmphylinmuesicarium (Wallr) simons, which is a fungus known as a fungus.
1.2.3 Garlic bacterial soft rot. Symptoms: After garlic is infected, it starts from the leaf margin or midrib, and forms yellow-white streaks along the leaf margin or midrib. It can penetrate the whole leaf. When the humidity is high, the diseased part is yellowish brown and soft. The foot leaves first develop, and then gradually expand to the upper part of the leaves, resulting in full yellow or death. In the field, the phenomenon occurred in the spot, and the disease occurred first in the water inlet. The field with poor terrain and poor drainage was seriously affected, and the incidence was heavy in November. The pathogen is the pathogenic type of Carrot soft rot fungus [Erwiniacarotovorasubsp. Carotovora (Jones) Bergeyetal], which belongs to the genus Bacillus.
Second, the countermeasures for yellow leaves in garlic
2.1 Agricultural control measures
2.1.1 Select a variety of disease-resistant products. As far as possible, use detoxification garlic, anti-disease garlic or the early garlic varieties selected by Chengdu Academy of Agriculture and Forestry, such as Chengjiazao No.3 and Chengjiaozao No.4.
2.1.2 Soil improvement. Calcium oxide (CaO) 750 kg/hm2 was used to neutralize the acidity and the decomposed organic fertilizer was applied.
2.1.3 Rotation. Choose garlic in the loam or sandy soil where the soil is rich in organic matter and has strong water and fertilizer retention capacity. Avoid continuous cropping or replanting with lily plants such as onion and garlic. The planting area should be kept away from pollution sources.
2.1.4 Deep trench high chamber cultivation. In the autumn season, Pengzhou has more rainy days in general years, and should be planted in high-cabin, which is good for drainage and reduces the degree of disease in the later period.
2.1.5 Scientific fertilization. When preparing the soil, the base fertilizer is applied to the mature organic fertilizer 30-45t/hm2, 45% compound fertilizer (15-15-15) 600-750kg/hm2, and zinc sulfate 15kg/hm2. Early topdressing, after emergence in the second to third leaf stage (early maturing varieties in late September fertilization, late maturing varieties in late October, fertilization) topdressing urea 75.0-112.5kg / hm2, this period of topdressing can effectively reduce the lack of "returning mother" The physiological yellow leaves appearing in the fertilizer can also be adjusted by spraying with 0.5% chitosan water-repellent agent 300 times to enhance the garlic resistance.
2.2 Chemical control measures
2.2.1 Garlic leaf blight. In the early stage of the disease, it is sprayed with methyl thiophanate 500 times solution, or 75% chlorothalonil 800 times solution, or 50% iphthora (hydantoin) wettable powder 1000-1500 times. Depending on the condition of the field, the application will be started at the end of November or late March, once in winter, and twice in spring.
2.2.2 Garlic leaf blight. In the early stage of the disease, 72% gram of dew 800-1000 times solution, or anti-virus 矾 400-500 times solution, or 69% angstrom manganese zinc 1000 times solution spray control.
2.2.3 Garlic bacterial soft rot. In the early stage of the disease, 72% agricultural streptomycin WP 3000 times solution or 400-500 times liquid spray can be used for prevention and treatment. Generally, prevention and control will begin in late October, and prevention before winter.
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