symptom

Apple brown spot mainly harms leaves and fruits. In the early stage of leaf disease, dark brown herpes appeared on the front of the leaf, with a diameter of 0.2-0.5 mm, single or continuous, and gradually expanded. With the deepening of the disease course, the symptoms evolved into three types: (1) concentric ring lesions. The focus was round and dark brown with a diameter of 65438 0-2.5 cm. There are countless black spots on the front, concentric rings, and grayish brown on the back. The diseased leaves gradually turn yellow, but the junction between the diseased area and the healthy area around the diseased spot remains green. When infected in the tender leaf stage, sometimes the lesions do not appear concentric rings, but form light brown round or nearly round withered spots with a diameter of 1-5mm(2). The lesions spread radially, and the branches formed needle-like stripes with slight protrusions. The lesion has no certain shape and can be spread all over the leaves. In the later stage, the diseased leaves turn yellow, but the surrounding area is still green. (3) Large mixed lesions. The focus is nearly round or several spots are connected to form an irregular shape, with a diameter of 0.5-3.0 cm, dark brown on the front and grayish brown on the back. The lesions are scattered in black spots with needle-like cords at the edge. In the later stage, the diseased leaves turned yellow, but the area around the lesion remained green at 1-2mm. The center of the old lesions was mostly gray.

It is difficult to completely distinguish the three types of symptoms in the later stage. Different varieties have different symptoms. Such as begonia, Vitex negundo and so on. Most of them are needle-like symptoms; Ruby, golden crown, marshal and other varieties form needle lesions and mixed large spots; Guoguang, Bailong and other varieties showed concentric annular lesions in the early stage of onset, and later evolved into mixed large spots. No matter what kind of symptoms, the common characteristics of the late onset are irregular edge of the lesion, unclear boundary with the healthy part, yellowing and shedding of the diseased leaves, and green around the lesion. There are scattered fly dung-like black spots on the lesion, that is, the sterile nucleus of the pathogen.

At the early stage of fruit disease, light brown spots appeared on the surface of the fruit, which gradually expanded, and were round, rectangular or shapeless, sunken, with a diameter of 6- 12 mm, and the surface turned black with protruding small black spots. The pulp of the affected part is dry and rotten, and it is brown and spongy.

Pathogen (Figure 1-9)

Figure 1-9 apple brown spot pathogen

1.acervulus 2。 Spores

The asexual stage of apple brown spot pathogen is apple brown spot pathogen. The funicle is composed of dark brown hyphae arranged in parallel, with many branches and passing under the epidermis. Porphyridium is buried under the epidermis of leaves or fruits, and mainly grows on the suspensor, especially at the bifurcation of the suspensor, 108—306×45—50μm, surrounded by a dark brown envelope composed of polygonal cells. Conidia are arranged in a grid, single-celled, colorless, unbranched, rod-shaped, with a blunt tip,15—20× 3—4 μ m. The conidia are terminal, colorless, twin-celled, the upper cell is slightly larger and round, and the lower cell is slightly narrow and sharp, like an inverted gourd,13.2-18.0× 7.2-8.4 microns, containing one or several oil balls of different sizes. Occasionally, single-celled conidia swell and gush out after absorbing water, showing gray fly dung and scattered in the disease.

In recent years, the sexual generation of Alternaria alternata is Alternaria Mali. Ascomycetes are formed on the diseased leaves, which are fleshy and discoid, with a diameter of 120-220μ m and a height of100-150μ m. Ascomycetes are rod-shaped to oblong, and 55-78×/kloc. Ascomycetes are oblong or ovoid, straight or slightly curved, usually with a partition wall, with slightly pointed or rounded ends, colorless, 23-33× 5-6 μ m, lateral filaments, 1-2 separated, colorless and 2-3 μ m wide.

Occurrence law

The pathogen of brown spot overwinters in the diseased leaves left by trees, or spreads on the ground as mycelium or funiculus. Spores are produced after the next spring rain, spreading infection. Humidity is a necessary condition for overwintering strains to expand and produce spores. Rotten diseased leaves cannot produce spores. In Laiyang, Shandong Province, after a dry winter, the overwintering conidia on fallen leaves still have germination ability. Conidia spread by wind and rain. The incubation period is generally 5- 12 days, and the longest is 45 days. It takes about 13-55 days from the onset to the shedding of diseased leaves.

Liaoning and Hebei producing areas began to get sick from late June to early July, and the peak period was from late July to August. In the old course of the Yellow River and the northern foot of the Qinling Mountains, the disease began in the middle and late May, and the peak period was July and August. In Yunnan, Guizhou and Sichuan, the disease began in the middle and late April, and reached the peak in late June, and the leaves began to fall. The severity of the disease varies greatly in different years. Rainy weather is the main condition for the epidemic of this disease. In years with early onset and rainy days, the onset is early and severe, and vice versa. Orchards with weak trees, closed crowns and poor ventilation and light transmission are seriously ill. The disease of young trees is light, and the disease of fruit trees is heavy. Marshal, Hongyu, Jinguan and Guoguang are susceptible to diseases, while Jiguan, Jiugui Lu and Zhu Zhu are resistant to diseases.

Prevention and cure method

1. Strengthen orchard management, enhance the disease resistance of trees, pay attention to orchard drainage, prune reasonably, improve ventilation and light transmission of canopy, and reduce diseases.

2. Remove fallen leaves from trees and the ground, and eliminate the main source of infection.

3. According to the onset period, spray medicine to prevent infection from about half a month before the onset. Liaoning producing areas generally need to spray drugs twice in early July and early August, and Hebei and Shandong require spraying drugs three times in mid-June, mid-July and mid-August; The old course of the Yellow River and the northern foot of the Qinling Mountains began to be treated in May, and then sprayed every 20 days 1 time; Yunnan, Guizhou and Sichuan should start prevention and control from the middle and late April, and it will take about 5-6 times to spray drugs. Drugs can be selected from 1: 2: 200 bordeaux solution, 700-800 times of 50% chlorothalonil solution, 600-800 times of 70% thiophanate methyl solution and 250-300 times of 25% carbendazim solution.