Why does magnolia turn yellow and keep falling leaves?

The symptoms of iron deficiency in Magnolia Officinalis generally begin in early May, with smaller leaves, green old leaves, green veins of new leaves and yellow or even white mesophyll. By the end of June, the leaf margin dried up and the whole leaf gradually withered. Because the activity of iron in plants is very weak, the iron in old leaves can not be transferred to young leaves, so when iron is deficient, the lower leaves tend to remain green, and the young leaves first appear yellowing phenomenon. Due to lack of nutrition, leaves wither, the tree is weak, flower buds cannot form, the whole tree cannot bloom, and its ornamental value is lost. We adopt the following three control methods: \ x0d \ 1. The time for foliar spraying fertilizer should be in the morning or evening. Add 0.3% ferrous sulfate to the foliar fertilizer and spray it evenly. Pay attention to the front and back of the blade and spray it until the blade drips. If it rains within 24 hours after spraying, it should be sprayed again every 7 days. It is not advisable to spray in the same place for too long, otherwise it is easy to produce fertilizer damage. \ x0d \ 2。 Punch and pour under the coronoid process, drill a hole about 40 cm deep every 50 cm, dilute ferrous sulfate into 50 times solution and pour it into the hole until it is full. /kloc-irrigate once every 0/5 days, four or five times in a row. At the same time, some fermented manure and urea solution can also be added. After 15 days, the new leaves began to turn green, and the green was distributed in dots on the leaves. \ x0d \ 3。 Base fertilizer should be applied after autumn or before germination in early spring. The method of radial furrow fertilization or annular furrow fertilization is adopted. When digging ditches, the root system should be damaged as little as possible, because the root of Magnolia grandiflora is fleshy and has a long healing period after injury. In order to expand the fertilization area, the position of ditches and holes should be changed every other year or once. The fertilization method of radial furrow is to dig furrow at a distance of 1 m from the trunk, which is shallow inside and deep outside, and the deepest part is 30 to 40 cm. Press 1? 5. Mix ferrous sulfate and fully decomposed organic fertilizer evenly, add some compound fertilizer at the same time, water it to fully dissolve it, and cover it with soil after water seepage. The number of furrows and holes, the amount and method of fertilization depend on the size of the tree. For example, Magnolia grandiflora with DBH of 12 cm can dig 5 to 8 ditches, using 5 kg of ferrous sulfate, 25 kg of organic fertilizer and 3 kg of compound fertilizer. Young magnolia trees should adopt ring furrow fertilization method. \x0d\ Three fertilization methods have good effects. For symptomatic trees, foliar fertilizer should be sprayed as soon as possible after all the leaves grow out in the second year, once every 7 days. After two or three years of careful management, magnolia can return to normal.