1 causes and its characteristics
1.1 physiologic yellow leaves
1.1.1 soil acidification.Acidic soil harm cause yellow leaves, neutral soil suitable for the growth of garlic, with pH 7.0 ~ 7.4 is optimum.When less organic fertilizer application, a large number of applying chemical fertilizer, compound fertilizer, calcium superphosphate) can make the soil acidification, cause slow growth of the garlic leaf, thin, outer leaves withered and yellow.
1.1.2 drought.Garlic do not pay attention to in the production of water, soil drought, plant water easy cause yellow leaves, less rainfall in the winter and spring seasons.
1.1.3 trace element deficiency.Calcium deficiency heart tip etiolation, physiological, tip yellow magnesium deficiency.
1.1.4 the toxic gases harm.One is the topdressing ammonium bicarbonate, can cause ammonia harm, blasted the tip, gradually become brown;Second, the factory emissions (CO) suffer rapid loss of green leaves, leaves start to turn pale, late leaf withered and yellow, disease of mildew and other symptoms.
1.1.5 physiology to take off the fat.At the early stage of the growth of garlic.Garlic emergence after 20 d tip began to miss green to dark brown, after tip withered and yellow, the field is uniform, no center strain.The reason is that "mother", also called physiology sex fat, kind of garlic in the storage of nutrients has run out, moss and cloves differentiation, if not timely fertilizer, yellow phenomenon occurs.
1.2 pathological yellow leaves
1.2.1 garlic leaf blight.Symptoms: major hazard, leaf disease started in other parts of the blade tip or blade and more early flowers white dots, enlarged irregular shape or oval shape, gray or beige disease spot on raw black mildew, serious when blade die.In pengzhou in early November began to come on, the following march into the incidence peak, average strain rate is above 20%.Pathogen for the fungus to ascomycotina withered leaves, spore cavity bacteria [Pleospora herbarum (Pers. Ex Fr.) Rabenk], fungi, imperfect fungi.
1.2.2 garlic leaf blight.Early symptoms: major hazard leaf, leaf disease in the central blade tip or having pale to light yellow water spots, light green edge and disease spot expanding fast, blade flag, when humidity is big on sparse gray mold, die disease spot.Production in October and the following year in March, is garlic recurrent disease.Agent to handle off day lily mildew [Stmphylinm uesicarium (Wallr) simons], imperfect fungi fungus.
1.2.3 garlic bacterial soft rot.Symptoms: garlic after infection, from the first leaf midrib or disease, along the margin or midrib yellowish-white streak, but throughout the entire blade, humidity is big, yellowish-brown soft rot disease department.Leaf apex foot disease, after gradually blades extend upwards, all yellow or death.Field performance for some, more in the water entry first onset, terrain depression, drainage adverse plots in heavy disease, heavy in November.Euclidean coli pathogen for carrot soft rot carrot type soft rot disease (Erwinia carotovora subsp. Carotovora (Jones) Bergeyetal], belong to the bacteria thin wall door.
