Why Are Orange Tree Leaves Turning Yellow? Causes and Solutions

During the Spring Festival, many people's homes certainly include an orange tree, but problems are inevitably encountered during the growing process. For example, yellowing leaves. The causes of yellowing leaves on orange trees are many-sided. Such as insect pests, infectious diseases, nutrient imbalance disorders (physiological diseases), etc. Below, the editor will introduce several causes of yellow leaves on orange trees and their solutions.

I. Insect Pests

1. Red spider mite: April-June and September-November are the peak periods of occurrence. It mainly damages citrus leaves, twigs and fruits. When the damaged leaves and fruits are severe, they turn grayish-white, lose their luster, and eventually wither, yellow and fall off.

Controlling red spider mite:

① You may choose 75% propargite 3000x solution, or 15% saomanjing 1000x solution for spraying (also controls rust mites);

② It is recommended to use 24% Envidor suspension concentrate 5000x produced by Bayer of Germany, with outstanding effect.

2. When orange leaves suddenly turn yellow, it is mainly caused by insects in the roots. If the roots are damaged by insects, the root bark is damaged, nutrients and water cannot be absorbed and transported, and the leaves will turn yellow because they cannot get a normal supply of water and nutrients.

II. Symptoms of Nutritional Imbalance in Citrus

1. Citrus nitrogen deficiency.

Damage symptoms: Leaves turn yellow, the leaves uniformly become light green, accompanied by nitrogen being transferred out of the leaves to maintain new growth.

① Measures: Strengthen management, apply more farmyard manure, and in combination with foliar topdressing, spray 0.2% urea plus 0.3% monopotassium phosphate or nutrient solution fertilizer at intervals of about 10 days. For mountain citrus orchards, add 0.2% borax spray.

2. Citrus iron deficiency disease.

Damage symptoms: Symptoms generally appear first on young shoots. Leaves become thin and yellowed, light green to yellow-white, with green veins, showing a clear green network pattern on the yellowed leaves, more obvious on the leaves at the tips of small branches. Diseased plant branches are slender and weak, and leaves on young branches fall off very easily, often leaving only sparse leaves. After the leaves on small branches fall off, normal branches and leaves grow only on the larger branches below, but the top branches die successively. When the disease is severe, all leaves of the whole plant turn orange-yellow.

Citrus iron deficiency disease is mainly caused by insufficient iron supply. According to reports, insufficient nitrogen fertilizer can also produce iron deficiency symptoms. Iron deficiency often occurs together with zinc deficiency, manganese deficiency, magnesium deficiency, etc.

Control methods:

① Improve the soil and fertilize. The fundamental method to prevent and control iron deficiency disease is to improve the soil and establish a good drainage and irrigation system to prevent drought and waterlogging disasters. For alkaline soil, apply more organic fertilizers, with special attention to applying more green manure, soil and miscellaneous fertilizers, and other acidic fertilizers.

② Apply iron sulfate. On the basis of improving the soil and establishing a good drainage and irrigation system, apply iron sulfate or spray 0.1% iron sulfate solution; part of the roots can be cut off to allow it to absorb iron sulfate. However, using iron sulfate for control without soil improvement has no obvious effect.

③ Apply 15-20 kg of sulfur powder per mu, and additionally apply ammonium sulfate, potassium sulfate, etc., to acidify the soil.

3. Citrus zinc deficiency disease.

Damage symptoms: New shoot leaves turn yellow, appearing yellow or yellow-green, while the main and lateral veins and the tissue near them remain green. The main and lateral veins of old leaves have irregular green bands, while the rest is light green to orange-yellow. Some leaves show only yellow and light yellow spots between the green main and lateral veins, and some leaves become smaller, narrower and lose their green color. When zinc deficiency is severe, the top twigs are slender and short, the leaves are upright, and the whole plant appears as an upright dwarf bush, after which the small branches die.

Control methods: Spraying 0.4%-0.5% zinc sulfate solution (with 1%-2% lime and 0.1% adhesive) before the spring shoot grows can effectively treat zinc deficiency disease. In addition, spraying 0.1%-0.2% zinc oxide can also correct it. For slightly acidic soil (pH5.5-6), applying a small amount of zinc sulfate can also achieve good results, but it is ineffective on alkaline soil. If zinc deficiency is induced by magnesium deficiency or copper deficiency, applying zinc salt alone has little effect, and compounds containing magnesium, copper and zinc must be applied at the same time to achieve good results. Secondly, applying more organic fertilizer is also very important.

4. Citrus boron deficiency disease.

Damage symptoms: Mature leaves and old leaves begin to yellow from the veins, eventually the whole leaf yellows, the mesophyll is relatively thick, and the leaf tips mostly curl backward; the veins swell, the main and lateral veins become corky, and in severe cases they crack. Tender leaves produce irregular water-soaked yellow spots and are distorted and deformed; some have water-soaked black spots at the base of the main vein on the underside of the leaf and fall off easily. On the rind of young fruit, milky-white slightly raised small spots appear, and in severe cases sunken black spots appear, with the mesocarp and fruit core filled with gum; this often causes young fruit to drop in large numbers. The remaining fruit is small and hard, with tumors on the rind surface, thick rind, little juice, aborted seeds, and gum filling the mesocarp and fruit core. When boron deficiency is severe in an orange orchard, a large number of leaves fall early, branches die, and sometimes the whole plant dries up.

Control methods:

(1) Apply boron fertilizer. Mix boron fertilizer into human excrement and urine, dig a trench under the tree canopy and apply it, cover with part of the organic fertilizer and then cover with soil. Adult trees are given 0.1-0.15 kg of boron fertilizer each time, and lightly diseased trees can be reduced accordingly. Generally apply once every 2-3 years.

(2) Foliar boron spray. Generally spray boron fertilizer (boric acid or borax solution) once each in early spring and full bloom, which can effectively prevent and control boron deficiency disease. In early spring, use a concentration of 0.5%-0.8%, afterward use 0.3%-0.4%, but in summer and autumn the concentration should be changed to 0.2%-0.3%. To prevent phytotoxicity, about 0.5% quicklime can be added. Spraying should be done on cloudy days, or in the early morning or evening of sunny days when the temperature is lower and the humidity is higher.

(3) Avoid excessive application of nitrogen, phosphorus and calcium fertilizers. Especially in soil with low organic matter content, even more attention should be paid not to apply too much nitrogen, phosphorus and calcium fertilizer. Barnyard manure should be applied, or farmyard manure and green manure with relatively high boron content. In acidic soil, excessive lime should also not be applied.

(4) In dry seasons, preserve water and water in time; in rainy seasons, pay attention 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, yellow-green, with the main and lateral veins and the tissue near them green, and the rest yellow-green, relatively similar to the symptoms of zinc deficiency disease. However, the yellowed part of zinc deficiency is very yellow, while that of manganese deficiency is greenish; the young leaves of zinc deficiency are small and narrow, while the leaf size and shape of manganese deficiency are basically normal, and old leaves also show symptoms. In severe cases, the leaves age and fall off early, new shoot growth is severely inhibited, and some die. If manganese deficiency is accompanied by zinc deficiency, more small branches die.

Control methods:

(1) Apply manganese sulfate. In acidic soil, manganese sulfate can be mixed with other fertilizers and applied. Lemon is relatively prone to phytotoxicity from manganese sulfate, so the number of sprays should be fewer and the concentration should be lower, and attention should be paid to this. For alkaline soil, a mixed solution of manganese sulfate and quicklime (0.2%-0.6% manganese sulfate plus 1%-2% quicklime) can be sprayed, neutralized and adjusted to (pH6-6.5), and the control effect is good in all cases.

(2) From May to August, spray 0.6% manganese sulfate and 0.3 degrees Baume lime sulfur mixture; or spray 0.3% manganese sulfate plus an equal amount of lime; in August, 0.4% manganese sulfate mixed with rosin mixture can also be sprayed.

(3) Apply more organic fertilizers such as composted barnyard manure or fermented green manure.

6. Citrus magnesium deficiency disease.

Magnesium deficiency disease is a micronutrient deficiency disorder. The leaves are yellow but the veins are green. You can get some soil from the wild, preferably fully stirring it with water from a rice paddy and then letting it clarify, to extract the trace elements from the soil. Watering the orange tree with this water is a relatively good method to solve the nutrient deficiency problem.

III. Tips for Caring for Orange Trees

Fertilization precautions

1. Apply heavy winter fertilizer

Before and after harvesting the fruit, in combination with deep plowing and soil improvement, apply heavy organic fertilizer, which has a significant effect on restoring tree vigor and promoting flower bud differentiation. The specific method is: in early to mid-December, dig deep trenches along the outer part of the tree canopy, and apply heavy base fertilizer (peanut bran, bone meal, soil and miscellaneous fertilizer, pig and cattle manure, compost, barnyard manure, phosphate rock powder, superphosphate, etc.). Applying heavy winter fertilizer is the foundation for a bumper harvest the following year. But it should be noted that winter fertilizer must be applied early and in large amounts (accounting for 50% of the annual fertilization amount), and should be mainly organic fertilizer.

2. Apply spring fertilizer early

Applying quick-acting nitrogen and phosphorus fertilizers before the spring buds of the orange tree sprout (late February to early March) has the effect of strengthening shoots and improving the quality of flowering branches (increasing the number of leaves and leaf area of flowering branches), and can promote normal sprouting of new shoots and supply the nutrients needed for fruit development.

3. Skillfully apply fruit fertilizer

Applying quick-acting nitrogen fertilizer in mid-to-late May can compensate for the nutrients consumed by flowering and allow young fruit to receive sufficient nutrition, reduce fruit drop, and increase the fruit-setting rate. From July to September, the fruit grows rapidly and a large number of autumn shoots are produced as the fruiting mother branches for the next year. Vegetative growth and fruit development often conflict over nutrients and water. At this time, topdressing with quick-acting nitrogen fertilizer, combined with phosphorus and potassium fertilizer, can accelerate fruit growth, improve fruit quality, and promote the occurrence of autumn shoots. But it must be noted: the type, concentration and method of fertilization should be determined according to tree growth and soil and weather conditions. In dry seasons, first water to keep the soil moist, then fertilize, which helps root absorption and achieves the effect of “water promoting fertilizer”. Applying fertilizer and water together is a method of skillfully applying fertilizer, which can make the same fertilizer play a greater role. For fruit trees with vigorous growth, too much nitrogen fertilizer should not be applied, otherwise when spring and summer shoots grow too vigorously, it will also cause fruit drop.

4. Foliar fertilization

Foliar fertilization is a topdressing method that uses the stomata and cuticle of leaves to directly absorb nutrients, and has the advantages of quick effect and high absorption and utilization rate. During the bud stage, flowering stage and young fruit stage, use water-soluble quick-acting fertilizers for foliar fertilization, which can increase the fruit-setting rate and facilitate fruit expansion and development.