In recent years, garlic is affected by many factors, and the phenomenon is more prominent, resulting in reduced production, reducing the quality of garlic, general field reduction of 10% to 30%, especially serious field crops. Yellow leaves of different etiology have increased the difficulty of prevention and treatment. Correct identification is the premise of prevention and treatment, and the best effect can be achieved by symptomatic medication.
1 causes and characteristics
1.1 physiological yellow leaves
1.1.1 soil acidification. Acid soils cause yellow leaves and neutral soil, which is suitable for garlic growth, and the pH value is 7 to 7.4. When the organic fertilizer is less, a large number of chemical fertilizer (fertilizer, superphosphate) will cause soil acidification, garlic leaf grow slowly, thin, yellow leaf.
1.1.2 drought. In the process of garlic production, the water is not dry and the soil is dry. The water shortage of the plant causes yellow leaves, which is common in the winter and spring with less rainfall.
1.1.3 deficiency of trace elements. Calcium deficiency heart tip yellow, physiological obstruction, magnesium deficiency, blade tip yellow.
1.1.4 toxic gas hazards. One is the nitrogen ammonium bicarbonate, ammonia can cause harm, make the tip withered, gradually become brown; two is the factory emission (CO) caused by the victims of rapid Leaf Chlorosis, leaf became gray white, yellow leaves of late disease without symptoms such as mold shaped.
1.1.5 physiological fertilization. Occurs during the prophase of garlic growth. Garlic seedling after 20 d tip to the loss of green tea after the tip into brown, withered and yellow, field performance for the onset of uniform, non center plant. The reason is "mother", also known as physiological Tuofei, garlic has been used in the storage of nutrients, flower buds and garlic began to differentiate, if not timely fertilizer, there will be yellow.
1.2 pathological yellow leaves
1.2.1 garlic leaf blight. The main symptoms: harm leaves, disease begins in other parts of the tip or leaf, white flowers at the beginning of a small dot, expanded irregularly shaped or oval gray white or grey brown spots, on the black mold shaped, serious leaf withered. The onset of the disease in Pengzhou city in early November, in March to enter the peak incidence, average strain rate is more than 20%. Pathogenic fungi ascomycotina leaves Alternaria bacteria [Pleospora herbarum (Pers.ex Fr. cavity) Rabenk], fungi deuteromycetes.
1.2.2 garlic leaf blight. The main symptoms: harmed leaves, leaves of infected leaves in the early middle or tip on the pale white to pale yellow water spots, light green edge, lesion expansion fast, drooping leaves, high humidity on the sparse gray mold, dead spots. Production in October and the following year in March damage, garlic often disease. Pathogen of daylily Stemphylium [Stmphylinm uesicarium (Wallr) simons], genus of fungi imperfecti fungi.
1.2.3 bacterial soft rot of garlic. Symptoms: garlic after infection from leaf margin or midrib formation streak disease, white leaf margin or along midvein, can be run through the whole leaf, high humidity, yellowish brown like soft rot disease department. Foot Ye Xian disease, and then gradually extended to the upper leaves, causing all withered or yellow or death. Field performance for the film, in the inlet of first onset, the incidence of depression, poor drainage field is heavy, was issued in November. The pathogens are carrot, soft rot, Erwinia, carrot, soft rot, pathogenic [Erwinia, carotovora, subsp.Carotovora (Jones) Bergeyetal], which belong to the bacterial community.
2 Countermeasures
2.1 agricultural control measures
2.1.1 selected varieties with high disease resistance. As far as possible the use of virus-free garlic, garlic resistance or selection of Chengdu Academy of agriculture and Forestry Sciences into the early series of garlic varieties, such as garlic early 3, garlic early 4.
2.1.2 soil improvement. Apply calcium oxide (CaO) 750 kg/hm2, neutralize acidity, and use decomposed organic fertilizer.
2.1.3 rotation. Select the soil rich in organic matter, water and fertilizer retention ability of the soil and sandy loam planting garlic, garlic and so avoid continuous cropping or Liliaceae crop cropping, the planting area should be far away from the source of pollution.
2.1.4 deep ditch high trunk cultivation. The autumn season, Pengzhou city general year rain day, should use the high compartment for drainage, planting, reduce the occurrence degree of late disease.
2.1.5 scientific fertilization. When the soil fertilizer applying decomposed organic fertilizer 30 ~ 45 t/hm2 and 45% compound fertilizer (15-15-15) 600 ~ 750 kg/hm2, zinc sulfate 15 kg/hm2. As early as topdressing, after emergence in two to three leaf stage (early maturing in late September to late October, late maturing varieties, fertilization, fertilization) Topdressing Urea 75 ~ 112.5 kg/hm2, this period of dressing can effectively relieve physiological leaves because of "mother retreat" Quefei appeared, also can use 0.5% chitosan bran water agent 300 times liquid spray regulation of the growth of garlic, garlic to enhance resistance.
2.2 chemical control measures
2.2.1 garlic leaf blight. In the early stage of the disease, 500 times of methyl methyl Ling, or 75% chlorothalonil 800 times, or 50% carbamide (Pu Haiyin) wettable powder, 1000~1500 times liquid spray, were used to prevent and control the disease. As the field condition at the end of November or late March began spraying prevention in winter 1 times, 2 times in control.
2.2.2 garlic leaf blight. At the early stage of the disease by 72% curzate 800 ~ 1000 times liquid or sandofan 400 ~ 500 times liquid, or 69% grams of mancozeb 1000 times liquid spray control.
2.2.3 bacterial soft rot of garlic. At the beginning of the disease, 72% streptomycin, wettable powder 3000 times, or 400~500 times liquid spray can be used to prevent and cure. General prevention in late October, heavy winter before the prevention and control.
