symptom
Mainly damage fruits, fruit stems and cobs, and also damage leaves when serious.
(1) Leaf: Off-white, round lesions appear at the time of onset.
(2) Cob: Round, oval or irregular lesions appear near the fruit grains, dark brown to grayish black, slightly sunken. Some cobs are dry, the fruit grains grow poorly, and the fruit surface is wrinkled. Pathogenic bacteria invade nearby fruit grains from the cob, and lesions occur.
(3) Fruit: The fruit surface is also infected. Fruit lesions dark brown to purple brown. Sparse small black spots are formed on the surface of cobs and fruit lesions. The diseased fruit becomes stiff fruit in the later stage and remains on the plant for a long time.
Pathogen
Physalospora baccae is called grape cyst, which belongs to the fungus kingdom Ascomycota. Ascus oblate or nearly spherical, dark brown, buried under the skin of the diseased tissue, with prominent orifice, 200μm×180μm in size. Ascus colorless, cylindrical. Ascospores are colorless, single cell, oval or spindle-shaped, size (15.3-24) μm×(6-9.5) μm, with lateral filaments between ascus, linear and colorless, with 2-3 septa.
The anamorphic type is MacroMacrophoma faocida. It is called Phomama faocida, which belongs to the anamorphic fungus of the fungal kingdom. The pycnidia are half-buried under the skin of the host, oval, dark brown, and the top orifice breaks through the epidermis to expose, and the size is (104-320) μm×(80-240) μm.
A dense layer of conidiophores grows densely on the inner wall of the pycnidia. The conidiophores are short, cylindrical, single-celled, colorless, 25-30 μm long, and conidia are continuously produced at the top. Conidia are oval or spindle-shaped, and the single cells are colorless, with a size of (16-24) μm×(5-7) μm.
Transmission routes and disease conditions
It mainly overwinters with pycnidia on diseased fruits, diseased cobs or diseased leaves. In areas where the ascus is produced for generations, the ascus shell is also the main overwintering organ. Some studies suggest that mycelium can also overwinter in diseased tissues and form asthecia in the spring of the following year.
After overwintering, ascospores or pycnidia release ascospores or conidia when the temperature rises, rainfall or high humidity conditions, and are spread by wind and rain or insects. The conidia germinate within 4 hours at 24-28°C. Ascospores can also germinate at 25°C for 5 hours. The bacteria adapt to the temperature limit of 9-40°C, and can develop diseases at 15-35°C.
The disease is a high-temperature and high-humidity disease, and the optimum temperature for mycelia to grow is 35°C. Therefore, high temperature, rainy and humid conditions after fruit coloring are favorable for its occurrence and prevalence. Rhodium blight is a facultative parasite, and the management is extensive, the growth of plants is weak, and the disease is serious in closed and humid vineyards.
Prevention method
(1) Agricultural control:
①Choose and plant disease-resistant varieties according to local conditions. American system grapes have strong disease resistance, such as Heihuxiang.
② In autumn, diseased branches, leaves, fruits, etc. should be thoroughly removed, and burned or buried deeply in order to reduce the source of infection at the beginning of the second year.
③Prune the grapes in time in summer from the long-term growth of new shoots, remove excess branches and vines, open the light path, save tree nutrients, increase the application of quick-acting nitrogen, phosphorus, and potassium compound fertilizers, and spray 0.3% to 0.5% dihydrogen phosphate on the leaves Potassium and urea mixture to enhance tree vigor and improve tree disease resistance.
In the rainy season, beware of a large amount of water in the garden to form a high-humidity environment to reduce the incidence of disease. After the leaves of the grapes fall in autumn, the diseased fruits, leaves and branches of diseased insects in the garden should be burned or buried deeply in time to eliminate the source of overwintering bacteria.
(2) Chemical control:
① After the grapes are put on the shelf in early spring, spray 3-5 Baume degrees lime sulfur mixture, and spray 70% thiophanate-methyl wettable powder 500-1000 times liquid on the whole tree 1-2 times (interval 8-10 days) for bud germination In the early stage, the whole tree is sprayed with Baume 3-5 lime sulfur mixture to eradicate the source of overwintering bacteria.
After the grape leaves are unfolded, from the period of ear formation, the whole tree is sprayed with 500 times of 50% carbendazim WP, or a mixture of 50% thiram cream and 80% anthracnose thiram WP 1500-2000 times. Spray once every 10 to 15 days, and spray 4 to 5 times in total, which can effectively control the occurrence of grape house blight, and also treat grape white rot and other diseases.
② For orchards with severe disease, they can be bagged to prevent disease after flower fall. Before bagging, 1:0.5:200 Bordeaux mixture should be sprayed once.
