1. Climate, too much fertilizer. Low winter temperatures, mechanical injuries, long sunny drought, improper use of pesticides, pests and diseases, fertilizers applied too much, especially acidic fertilizers applied too much, the old leaves turn yellow in the winter occurred a lot of defoliation, defoliation number more than 80%, the heavy plant defoliation of 100%, there are part of the pomelo orchard large areas of defoliation, most of the pomelo tree old leaves in the new shoots did not spit buds or spit buds began to a large number of defoliation is also quite common.

2. Winter boron poisoning. If each pomelo tree with more than 2 two borax applied to the soil, the old leaves turn yellow in winter boron poisoning occurs, before the big cold began to a large number of old leaves fall, the number of leaves fall more than 90%, a large area of the victim, the spring, although there is a growth of new leaves, but fewer buds, buds, after the results of the results of the poor fruit, fruit smaller, the climate is poor, the winter fertilizer is applied to too much type of mixing, fertilizer is close to the tree around the consecutive days of rain and low temperatures, the day turned sunny! High temperatures after the occurrence of root injury, root rot caused by defoliation, the climate for a long time under drought conditions, ring peeling too early wound greater than 1 centimeter or more, into the results of the grapefruit tree after deep turning and breaking the big roots expanding the hole, caused by a large number of defoliation, deep turning, breaking the big roots, expanding the hole after the general cause of defoliation.

3. Pesticides mixed with high concentration of the cause. Spring serious drug damage spots, leaf chlorophyll damage, leaf chlorophyll poor, winter leaf yellowing, occurring a large number of leaves, poor drainage of the flat pomelo orchard, winter deep turning soil, expanding the hole, spring rains, hole and the ground water accumulation of rotten roots caused by the weak tree leaf drop.

4. Acidic fertilizers applied in excess of more than the cause. Preferential application of heavy application of calcium, potassium sulfate, potassium chloride, soil acidity aggravated, the land Ban knot, a variety of elements caused by the loss of leaves.

5. The cause of serious pest damage. If the leaves are yellow in late fall and early winter, a large number of leaves fall in cold winter.

For the above several causes of defoliation: the following measures.

(1) Strengthen the management of the pomelo orchard. The details in the orchard will be handled well, so that from the outside, change the occurrence of defoliation.

(2) Increase the application of farmyard fertilizer. Farmer's fertilizer is rich in most of the elements needed by the grapefruit tree and causes few side effects, which is very suitable for application.

(3) Nitrogen, phosphorus, potassium matching appropriate. Increase the application of calcium and magnesium phosphorus, reduce the application of calcium superphosphate, and apply lime to change the acid once a year in summer to increase the land calcium content.

(4) Spring and young fruiting period with one and a half borax + potassium dihydrogen phosphate - two and a half + 100 pounds of water each spray 1-2 times.

(5) fruit trees and old trees in winter to shallow plowing, not deep turning without breaking the root, only in the periphery of the tree crown shallow plowing weed cultivation, especially applied to paddy field orchards should pay more attention to achieve the protection of the root growth, to maintain the perennial tree leaves evergreen purpose, the old pomelo tree ring peeling in the winter each plant to leave the Department of one to two twigs do not ring peeling to achieve the root of the tree to protect the strength, and to prevent the leaves from falling to reduce the amount of flowers, to achieve the fruit to increase the production of purpose.