Why Are There So Many Sunburned Citrus Fruits This Year?

It's another citrus harvest season. From a distance, the citrus orchard is full of bright red "little lanterns"; up close, a unique fresh fragrance of oranges wafts over, making your mouth water.

However, there are joys and sorrows for different people. In this busy autumn, many farmers complained to us that the purchase price of citrus this year is quite good, but the yield and quality are not satisfactory. There are too many "sunburn scars" (sunburned fruits) this year. Due to quality problems, the purchase price is lower than that of others, which is really worrying.

The citrus - producing area in Yichang, Hubei was a big - yield year for citrus last year. Coupled with the drought during the mature period and the severe cold winter, the citrus trees were greatly damaged. It's imaginable that the yield this year won't be very high. But during the fruit - strengthening period this year, there was continuous high temperature, which had an impact on the quality of citrus. Due to insufficient preparation, a large number of sunburned fruits appeared. In many orchards, a large number of fruits were sunburned and dropped, which was really distressing.

Causes of Citrus Sunburn Disease

Mainly at noon and in the afternoon during high - temperature weather, the local temperature of orange trees directly exposed to sunlight rises sharply. When it rises above 40 °C, the chlorophyll in the leaves gradually decomposes, the leaf color fades or turns yellow, and a large number of leaves fall after rain. The affected parts of the fruit initially turn gray - blue, then turn yellow - brown. The growth of the fruit peel stagnates, becomes rough and thick, and sometimes cracks, deforming the fruit, seriously affecting the quality of the fruit. The epidermis of the affected citrus branches turns yellow and red, and cracks appear until the cortical tissue necroses. Sunburn disease generally occurs more on the sunny side of the tree, on fruits and branches with a longer sunshine duration.

Preventive Measures for Sunburned Fruits

1.Strengthen Fertilization and Water Management

When entering the high - temperature and drought period in July, irrigation should be carried out in a timely manner to meet the water demand of citrus. Generally, water should be poured once every 7 to 10 days of continuous drought.

Combined with applying fruit - strengthening and shoot - promoting fertilizers, in addition to applying a certain amount of nitrogen fertilizer, it is also necessary to apply phosphorus and potassium compound fertilizers in combination. This can not only reduce the occurrence of sunburn disease but also promote the coloring of fruits. In addition, pay attention to the supplementation of elements such as calcium, magnesium, potassium, and boron, which can increase the toughness of the fruit peel and its water - retaining and water - transporting capacity, reducing the occurrence of sunburned fruits.

2.Cover the Tree Basin to Retain Moisture and Cool Down
In summer, around the tree basin, at the root - dense area vertically downward along the tree crown, spread fresh grass or straw and other coverings 10 to 13 centimeters thick to retain moisture and cool down, promote root activity, regulate soil moisture and the micro - climate in the citrus orchard, and promote the normal development of fruits. For base fertilizers, Yishizhuang citrus formula fertilizer and Yishizhuang organic fertilizer can also be applied, which can effectively promote the growth of new roots and has the effect of soil improvement.

3.Spray Fruits with Lime Water
In places where sunburn disease occurs seriously, 1% to 2% lime water can be sprayed on the outer fruits and leaves on the sunny side. It's like covering a white film, which can reflect strong light, reduce leaf temperature, and protect fruits and leaves. However, it should be noted that the concentration of lime water should not be too high to avoid penetration and causing phytotoxicity.

4.Whitewash the Tree Trunk
There are various formulas for whitewashing agents, but the formula of 10 parts of quicklime, 1 part of table salt, 0.2 parts of animal oil, and 40 parts of water has a better effect on preventing sunburn disease.
Apply it once in June, July, and September. Use a soft brush to apply it to the main trunk and large branches. The amount should be such that it doesn't flow down, doesn't stick into a ball, and can be thinly coated. In summer, when applying the whitewashing agent, the quality of quicklime must be good. It is best to be white lumps, and the digestion should be thorough. Otherwise, it will continue to absorb water and release heat on the tree, burning the branches and causing more serious damage. According to experimental observations, the temperature of branches coated with the whitewashing agent can be reduced by about 10 °C compared with those not coated during high - temperature periods, so it can play a protective role.

5.Stick White Paper on the Fruit Surface
For the fruits on the top of the tree crown and on the outer periphery of the southwest side, stick a small white paper similar in size to the fruit on the sunny side of the fruit, which can effectively prevent the burning of the fruit surface.

6.Clear Ditches to Drain Waterlogging and Induce Roots to Grow Deep
During rainy periods, ditches should be opened in a timely manner to drain water, improve soil aeration, induce roots to grow deep, and enhance water - absorption capacity, which can reduce the occurrence of sunburn disease.

7.Appropriately Release Late Summer Shoots to Shade the Fruits
Releasing late summer shoots appropriately to shade the fruits and reduce the surface temperature of the fruits can be a very good and cost - effective means to prevent sunburn

(Compiled from the Internet)