The cause of yellowing of orange leaves and its solution

During the Spring Festival, many citizens must have orange trees in their homes, but there will inevitably be some problems in the process of breeding. If the leaves are yellowing, there are many reasons for the yellowing of orange leaves. Such as insect pests, infectious diseases, nutritional imbalance (physiological diseases) and so on. The following editor will introduce the causes and solutions of the yellow leaves of orange trees.

I. insect pests

1. Red spider: the occurrence peak is from April to June and from September to November, which is mainly harmful to citrus leaves, shoots and fruits. The injured leaves and fruits turn grayish white and lose luster when they are serious, until they turn yellow and fall off.

Control red spiders:

① can choose 75% propargite 3000 times solution or 15% promethazine 1000 times solution spray (and control rust wall lice)

② recommends to use 24% mite dangerous suspension agent produced by Bayer in Germany, which is 5000 times, and the effect is outstanding.

2. Orange leaves suddenly turn yellow, mainly caused by insects in the roots. If the root is damaged by insects, the root bark is damaged, nutrients and water can not be absorbed and transported, the leaves will turn yellow if they do not get normal water and nutrient supply.

II. Symptoms of nutritional imbalance in citrus

1. Citrus is short of nitrogen.

Symptoms of damage: the leaves turn yellow, and the leaves turn light green evenly, accompanied by the transfer of nitrogen from the leaves to maintain new growth.

① measures: strengthen management, increase the application of farm manure, combined with extra-root topdressing, spray 0.2% urea plus 0.3% potassium dihydrogen phosphate or nutrient liquid fertilizer every 10 days, and add 0.2% borax spray to mountain orange orchards.

2. Citrus iron deficiency disease.

Symptoms: generally tender shoots show symptoms first, the leaves become thin and yellowish, light green to yellow-white, the veins are green, showing obvious green reticulation on the etiolated leaves, especially in the leaves at the top of the branchlets. The branches of diseased plants are delicate, and the leaves on young branches are easy to fall off, and there are often only sparse leaves. After the leaves of the branchlets fall off, the normal branches and leaves grow on the larger branches in the lower part, but the top branches die one after another. When the disease was serious, the leaves of the whole plant turned orange.

Citrus iron deficiency disease is mainly caused by insufficient iron supply. it is reported that iron deficiency will also occur when nitrogen fertilizer is insufficient. Iron deficiency often occurs with zinc deficiency, manganese deficiency, magnesium deficiency and so on.

Prevention and control methods:

① improved soil and fertilized fertilizer. The fundamental way to prevent and cure iron deficiency is to improve the soil and improve the drainage and irrigation system to prevent the occurrence of drought and waterlogging. More organic matter fertilizer should be applied to alkaline soil, especially green manure, soil miscellaneous fertilizer and other acidic fertilizers.

Ferric sulfate was used in ②. On the basis of improving the soil and improving the drainage and irrigation system, ferric sulfate is applied or 0.1% ferric sulfate solution is sprayed; iron sulfate can be inhaled by cutting off part of the root. However, the control effect of ferric sulfate without soil improvement is not obvious.

③ applied 1520kg sulfur powder per mu, ammonium sulfate, potassium sulfate and so on to acidify the soil.

3. Citrus zinc deficiency disease.

Symptoms of damage: the leaves of the new shoots were yellow or yellowish green, and the main and lateral veins and their nearby tissues were still green. There is an irregular green band in the main lateral vein of the old leaf, and the rest is light green to orange. Some leaves show only yellow and yellowish spots between the green main and lateral veins, while others become smaller, narrower and chlorotic. When the zinc deficiency was serious, the tip of the apical branch was short, the leaf was erect, and the whole plant was erect, and then the branchlets died.

Prevention and treatment: spraying 0.4% 0.5% zinc sulfate solution (plus 1% 0.2% lime and 0.1% adhesive) before spring shoot growth can effectively treat zinc deficiency. In addition, 0.1% zinc oxide can also be sprayed to correct the disease. For (pH5.5~6) slightly acidic soil, applying a small amount of zinc sulfate can also obtain a good effect, but it is not effective for alkaline soil. If zinc deficiency is caused by magnesium deficiency and copper deficiency, the effect of single application of zinc salt is not significant, and the compounds containing magnesium, copper and zinc must be applied at the same time to get a good effect. Secondly, it is also important to increase the application of organic fertilizer.

4. Boron deficiency in citrus.

Symptoms of damage: adult and old leaves yellowed from veins to whole leaves, with thicker mesophyll, leaf tips curled backward, veins swollen, cork of main and lateral veins, and severe cracking. The young leaves produce amorphous watery macula and twist deformities; some have water-like black spots at the base of the main vein on the back of the leaves, which are easy to fall off. Milky white protruding spots occur on the young pericarp, sunken black spots appear in severe cases, and the mesocarp and core are filled with colloid, which often causes a large number of young fruits to fall off. The residual fruit is small, hard, with tumors on the surface of the pericarp, thick pericarp, less seed abortion of fruit juice, and gelatinized mesocarp and core. When the orange orchard is seriously boron deficient, a large number of leaves fall early, the branches die, and sometimes the whole plant dries up.

Prevention and control methods:

(1) applying boron fertilizer. Boron fertilizer was mixed into human feces and urine, trenched under the canopy, covered with organic fertilizer and covered with soil. When 0.1kg-0.15kg boron fertilizer was applied to adult trees, the amount of boron fertilizer in lightly diseased trees could be reduced. It is usually applied once every 2-3 years.

(2) boron was sprayed outside the root. Generally, boron fertilizer (boric acid or borax solution) is sprayed once in early spring and full flowering stage, which can effectively prevent and cure boron deficiency disease. Spray 0.5%-0.8% concentration in early spring, then 0.3%-0.4% concentration, but change to 0.2%-0.3% concentration in summer and autumn. In order to prevent drug damage, about 0.5% quicklime can be added. Spray dosage should be selected in cloudy days, or in sunny morning and evening when the temperature is low and the humidity is high.

(3) avoid excessive application of nitrogen, phosphorus and calcium fertilizer. Especially in the soil with low content of organic matter, we should pay more attention not to apply too much nitrogen, phosphorus and calcium fertilizer, and should apply manure, farm manure and green manure with high boron content. In acid soil, it is not suitable to apply too much lime.

(4) in dry season, water should be preserved and watered in time, and in rainy season, attention should be paid to drainage to prevent the loss of available boron.

5. Citrus manganese deficiency disease.

Damage symptoms: the leaves of young branches are normal in size, yellowish green, the main and lateral veins and their surrounding tissues are green, and the rest are yellowish green, which is similar to the symptoms of zinc deficiency disease. But the yellowing part of zinc deficiency is very yellow, manganese deficiency is greenish, the young leaves of zinc deficiency are small and narrow, the size and shape of manganese deficiency leaves are basically normal, and the old leaves also show symptoms. In severe cases, the leaves aged and fell off in the early stage, and the growth of new shoots was seriously inhibited, and some of them died. If there is lack of manganese and zinc, the twigs will die more.

Prevention and control methods:

(1) Manganese sulfate was applied. Acid soil can be used with manganese sulfate mixed with other fertilizers, lemon is easy to cause drug damage to manganese sulfate, spraying times should be less, concentration should be small, attention should be paid. Alkaline soil can be sprayed with a mixture of manganese sulfate and quicklime (0.2%-0.6% manganese sulfate plus 1%-2% quicklime), neutralized and adjusted to (pH6~6.5), and the control effect is good.

(2) from May to August, 0.6% manganese sulfate and 0.3 Baomedusite sulfur mixture can be sprayed, or 0.3% manganese sulfate plus the same amount of lime can be sprayed; 0.4% manganese sulfate plus turpentine mixture can also be used to spray wine in August.

(3) apply more organic fertilizers such as compost or retting green manure.

6. Magnesium deficiency in citrus.

Magnesium deficiency is a kind of microelement deficiency, the leaves are yellow but the veins are green, you can get some soil in the field, it is better to stir the water in the paddy field to clarify and extract the trace elements from the soil. Watering orange trees with this kind of water is a better way to solve the problem of element deficiency.

Third, the experience of orange tree conservation.

Matters needing attention in fertilization

1. Heavy application of winter fertilizer

Before and after fruit picking, combined with deep ploughing to improve soil and re-application of organic fertilizer, it played a significant role in restoring tree potential and promoting flower bud differentiation. The specific measures are: from November to early December, deep trenches can be opened along the crown, and base fertilizers (peanut bran, bone meal, soil manure, pig and cow manure, compost, barnyard manure, phosphate rock powder, calcium superphosphate, etc.) can be re-applied. The heavy application of winter fertilizer is the basis of high yield in the coming year. But it should be noted that winter fertilizer must be applied early and more (accounting for 50% of the total amount of fertilizer applied in the whole year), and mainly organic fertilizer.

2. Early application of spring fertilizer

The application of available nitrogen and phosphate fertilizer before the spring bud germination of orange trees (from late February to early March) can strengthen the shoots and improve the quality of flower branches (increasing the leaf number and leaf area of flower branches). It can promote the normal germination of new shoots and provide nutrients for fruit development.

3. Skillfully applying fruit fertilizer

The application of available nitrogen fertilizer in the middle and late May can compensate the nutrients consumed by flowering, make the young fruit get enough nutrition, reduce the fruit drop and increase the fruit setting rate. The fruit grows rapidly from July to September, and a large number of autumn shoots are extracted. As the mother branch of the following year, vegetative growth and fruit development often compete for nutrients and water. At this time, the application of available nitrogen fertilizer combined with phosphorus and potassium fertilizer can accelerate fruit growth, improve fruit quality and promote the occurrence of autumn shoots. However, it must be noted that the types, concentrations and methods of fertilization should be determined according to tree potential growth and soil and weather conditions. In the dry season, watering should be carried out first to keep the soil moist, and then fertilization is beneficial to root absorption and achieve the effect of "water promoting fertilizer". The combination of fertilizer and water is a method of skillfully applying fertilizer, which can make the same fertilizer play an important role. For vigorous fruit trees, it is not appropriate to apply too much nitrogen fertilizer, otherwise when the spring and summer shoots are too full, it will also cause fruit drop.

4. Extra-root fertilization

Extra-root fertilization is a topdressing method which uses stomata and stratum corneum of leaves to infiltrate nutrients directly. it has the advantages of quick effect and high absorption and utilization. External fertilization with water-soluble available fertilizer at bud stage, flowering stage and young fruit stage can increase fruit setting rate and facilitate fruit expansion and development.