Spruce bud rust

Spruce bud rust is a newly discovered disease in the northern forest region of China, which has been reported in the natural forest region of Xing'an Mountains. It is mainly distributed in the United States, Canada, Sweden and other countries abroad, harming white spruce, black spruce and European spruce, harming the terminal and lateral buds of seedlings, young trees and big trees, and seriously affecting the quality of seedlings and the normal growth of plantations.

Symptoms appear when new leaves begin to grow in late May. During the same period, diseased buds grew faster and longer than healthy buds, but soon stopped growing. The diseased leaves from the diseased buds are grayish white and gradually turn yellow or purplish red. The diseased leaves are swollen and round, and the length of the diseased leaves is only about 9mm, which is less than half of that of the healthy leaves. The longest new diseased branch is 6.5cm. The newly diseased branches and leaves are like a flower and are often mistaken for spruce cones. A small black spot begins to grow at the tip of the diseased leaf, which is the sexual spore organ of the pathogen. The sporangium is gradually extended to the lower part. Then there were long orange strips, which were the spring spore organ of the pathogen, which were arranged in double rows on the inside of the leaves and single rows on the outside of the leaves. After the spring spores matured, many yellow powdery spring spores were emitted by the broken spore, leaving a very short white membrane coating on the diseased leaves. The disease buds soon withered and shrunk to black. After the terminal bud loves to harm, the seedling shows the form of decentralization. After years of victimization, it becomes a clump of branches.

Pathogen ChrysomyxaworoniniiTranz. It is called Fuluning golden rust, which belongs to basidiomycetes subphylum fungi. The sexual spore organ of the pathogen is mostly in the middle and upper part of the leaf. The leaf base is very few, and the size is 10.0-17.5 μ m × 10.0-14.0 μ m. The sexual spores are colorless, round or oval, 1.0-1.2 μ m × 3.0-3.5 μ m. Spring spores are unicellular, yellow, oval or round, serial, with verruca on the surface, and the size is 19.5-46.9 μ m × 13.7-38.5 μ m.

The pathogen overwintered in the diseased bud with hyphae, and the disease began in late May. With the growth of diseased leaves, the epigenetic spring sporangia, spring spores and spring spores began to release at the beginning of June, and the diseased shoots began to die in the middle and late June. The onset period is only about 30 days. The incidence of seedlings and young trees under canopy was higher than that without shade, and the incidence of big trees on shady slope was higher than that on sunny slope. In terms of a tree. In most cases, the incidence of terminal buds of shady branches is high. The diseased branches and buds withered in the middle and late June, and the onset period was only about 30 days.

Prevention and cure method

(1) Agricultural prevention and control.

When afforestation, select the land with few suspicious hosts for afforestation; in the nursery, check whether the seedlings are infected in late May. Once the disease is found, cut off the diseased branches and buds, put them in plastic bags, take them to the nursery and bury them or burn them, so as to prevent the spread of spring spores.

(2) Pesticide control.

In the early stage of the disease, spray 75% chlorothalonil or 1000 times of dichlorothalonil to the seedlings in time for prevention and control.

Commonly used agents chlorothalonil, diphacinone sodium.