Citrus Huanglongbing, also known as yellow shoot disease, is another quarantine disease among citrus diseases. Occurred sporadically in some provinces (autonomous regions) in China. At the early stage of the disease, the leaves of new shoots of some big branches turn yellow, showing the symptoms of yellow shoots. In summer and autumn, the number of yellow branches is small and often appears at the top of the crown; In the spring shoot stage, there are many yellow shoots, which appear at the top of the crown and other parts of the crown. It generally takes 1 ~ 2 years to spread from some branches to the whole plant. The diseased branches are easy to shed leaves, and the new buds sprouted from the diseased branches are short and the leaves are small and yellow.

There are three types of leaf yellowing: ① Uniform yellowing. The young leaves did not turn green, but showed uniform yellow. This symptom mostly occurs in the summer and autumn shoots of bananas and oranges. ② mottled and yellow. After the leaves turn green, they begin to turn yellow near the leaf base and veins, forming yellow-green spots, and finally the whole leaves can turn yellow. When plants begin to get sick, most of them show this symptom; Almost all patients who started to get sick in the spring beat showed this symptom. The new buds sprouting from diseased branches grow vigorously, which also shows this symptom. ③ Lutein deficiency. Veins green, mesophyll yellow, similar to zinc deficiency and manganese deficiency symptoms. This symptom rarely appears in the early stage of plant disease, and more often appears in the new buds of diseased branches. In the above three types of yellowing, mottled yellowing of leaves is the most characteristic. In addition, the diseased leaves are thicker than the healthy leaves, feel like leather, stand upright on the branches, some have swollen veins, and some are corked and cracked.

The diseased trees bloom early, with many flowers, a large proportion of deformed flowers and serious fruit drop. The diseased trees have small fruits, some of which are deformed into oblique shoulders, and the yellow and green are uneven when colored. Fuju, Ponkan, Satsuma and other wide-skinned oranges are often colored near the pedicel first, and the rest are turquoise, forming a "red nose fruit". Sick trees rarely grow new roots, and old roots often rot from fine roots. In the orchard under extensive cultivation and management, the diseased trees have many dead branches and can survive for a long time. Generally, the symptoms of branches and leaves appear first, sometimes the symptoms of fruits appear first, and the symptoms of branches and leaves appear the next year.