Occurrence and control of sunburn in citrus

Citrus sunburn is a common physiological disease in high temperature season, which mainly harms leaves, fruits and bark. The occurrence of the disease is mainly caused by high temperature and hot sun exposure. In the noon and afternoon of high temperature weather, the local temperature of the orange tree exposed to direct sunlight rises sharply. When it rises to more than 40 ℃, the chlorophyll of the leaves gradually decomposes, the leaves become lighter or yellowing, a large number of leaves fall after rain, and the fruit epidermis appears abnormal color. Such as high temperature for many days, the fruit surface is scorched yellow or brown, the pericarp sinks and hardens at the discoloration, the stem epidermis turns yellow and red, resulting in cracks, and then goes deep into the cortex until the cortical tissue is necrotic.

Sunburn usually begins in July, occurs most frequently from August to September, and usually occurs in sunny fruits in the southwest of the tree. Long sunshine time and insufficient soil moisture can aggravate the occurrence of sunburn. Under the condition of high temperature and hot sun, the use of stone-sulfur mixture to control citrus diseases and insect pests can also aggravate the disease.

To control citrus sunburn, in addition to irrigation to fight drought, the following measures can also be taken:

1. Spray fruit with lime water. In places where sunburn is severe, spray the front of the leaves on the upper part of the sunny crown with 1% limewater. After spraying lime water, it is like a white film, which can reflect strong light, reduce leaf temperature and protect leaves.

2. The trunk is painted white. Use 0.5 kg of quicklime and 2.5 kg of water to turn into lime milk and whiten the main branches that are exposed to direct sunlight. The temperature of the white bark is about 10 ℃ lower than that of the unwhitened bark at high temperature, which can avoid direct sunlight on the branches and play a protective role.

3. Fruit veneer or bagging. For the fruits at the top of the crown and the southwest of the periphery, a small piece of newspaper of 5cm × 7cm is affixed to the sun surface of the fruit, which can effectively prevent the burns on the fruit surface. In order to prevent the rise of fruit temperature, fruit bagging can also be carried out, or water evaporation inhibitor can be sprayed on the fruit surface to reduce water evaporation.

4. Open ditches and drain in time when it is rainy. Improve soil aeration, induce deep roots, and enhance the water absorption capacity of citrus trees.

Do not use stone-sulfur mixture to control pests in orange orchard from May to September. When it must be used, it is necessary to reduce the concentration and number of times. The concentration should be 0.1mi 0.2 degrees, 1 Mel can be sprayed twice, and spray evenly, so as not to make the liquid agglomerate too much on the fruit surface.