The early defoliation of apples seriously affects the growth and development of trees and fruits. Early defoliation reduces the production and accumulation of organic nutrients, which directly affects flower bud differentiation and fruit development in the later stage. In severe cases, the apple trees bloom again in autumn, the tree vigor is weakened, and the resistance of the tree body is reduced, which leads to the decline of apple yield and quality in that year, even in the second and third years.
There are many reasons for early defoliation of apples, including early defoliation caused by infectious diseases (brown spot disease, gray spot disease, round spot disease, mottled defoliation disease, etc.). ); Early defoliation caused by pests (mites, golden moths, pear nets, stinkbug, cicadas, etc.). ); Early defoliation caused by the lack of elements in the tree, if the young leaves of the tree turn green and the mesophyll turns yellow due to iron deficiency, the leaves will die and fall off in severe cases; Early defoliation is caused by improper management, such as increasing pesticide concentration at will when spraying, using unqualified pesticides containing harmful substances, uneven mixing of liquid medicine when spraying, causing chemical damage to leaves and causing early defoliation; The concentration of quick-acting fertilizer (especially nitrogen fertilizer) is too high, the input of organic fertilizer is insufficient, and the balance relationship between nutrient elements in trees is destroyed, which affects the absorption and utilization of some elements and causes early defoliation; Bad environment can also cause early defoliation, such as high temperature and drought in summer, when the temperature is above 34℃, if the soil moisture content in orchard is low and can not meet the needs of trees, the physiological adjustment of trees is unbalanced, resulting in self-thinning of leaves and early defoliation; Rainy days for several days, sunny days after rain, because the leaves can not adapt to the sudden change of climate, resulting in dry leaves, causing early defoliation (this phenomenon is more prominent in Jinguan varieties); The orchard crown is closed, and poor ventilation and light transmission will also cause early defoliation. In addition, due to the difference of disease resistance among varieties, the incidence of early defoliation varies greatly among varieties, such as Matsumoto Jin and Meng, which have poor resistance to early defoliation.
To prevent early defoliation of apples, it is necessary to distinguish the reasons and take corresponding measures to get good results. Thoroughly remove diseased leaves in autumn, and focus on burning or burying. Spraying drugs in time during the growth period, such as chlorpheniramine and baolian (mostly from cycloserine and kesheng). And it is usually sprayed 4 ~ 5 times. Acamycin and pyridaben can be used to control red spiders. Pyrethrin and imidacloprid can be used to control pear net stinkbug. Be sure to apply pesticides according to the effective concentration range and minimum effective dose specified by pesticides. The trees with poor ventilation and light transmittance are shaped to make the light transmittance of the orchard reach above 35% ~ 40%. Topdressing during the growth period should be increased or decreased according to the age of the tree, the tree potential, the amount of fruit left, the cultivation conditions and the types of fertilizers. It is not suitable for excessive fertilization, so we should pay attention to fertilization methods to ensure the balanced nutrition of trees. In case of drought, the orchard water should be managed in time (to keep the soil water content in the orchard up to 60% ~ 80%), and it should be discharged quickly in case of waterlogging. (Shijiazhuang Fruit Research Institute, Provincial Academy of Agricultural Sciences)