Melon powdery mildew symptoms
It is mainly harmful to the leaves, but also to the petiole and stems. In the early stage of the disease, white powdery mildew spots appeared on the front of the leaves, and later spread to the back of the leaves, which quickly expanded to form a white powder layer, which in severe cases extended to the back of the leaves, stems and petioles. The stalks are the same as the leaves. At the beginning, white powdery spots appear on the stems, and finally the whole stems are covered with white powder. At the late stage of the disease, the whole plant was covered with white powder layer, and the white powder layer turned grayish white. The white powder layer appeared scattered or piled yellow-brown, small grain spots, and later turned black, that is, the bacteria had a sexual generation of closed capsules, and the diseased leaves were dried. It becomes brittle, causing the fruit to grow slowly in the early stages. After the cure, it will leave marks on the lesions.
It should be distinguished from the white powder on the leaf surface: the leaves of the plant are yellow, and the surface of the leaf is sprayed with a large amount of pesticide powder and a layer of white powder is easily confused with the pathogen to suspect powdery mildew. Looking at the whole plant in the field, there is no white mildew in the leaves. The phenomenon of yellowing is related to mechanized application. Excluding the disease should be related to the phytotoxicity.
Melon powdery mildew
Melon powdery mildew is mainly caused by powdery mildew of Ascomycota and Monosporium melon. Both the sexual and asexual states of the pathogens can be overwintered, and the sexually closed capsules are left over the winter with the diseased bodies or on the melon crops in the greenhouse or plastic greenhouse. The ascospores released in the spring of the next year become the source of initial infection. In the asexual state, the hyphae or conidia are overwintered on the host, and the mycelium can be attached to the surface of the leaf for infestation, while the conidia produce a germ tube or aspirator to invade the epidermis of the host leaf under suitable conditions. The long-distance transportation of diseased seedlings is the main source of primary infection in disease-free areas. Airflow is the main route of melon powdery mildew. Pathogen spores spread with the airflow in the field or in the greenhouse. Ascospores or conidia can germinate under suitable conditions and invade directly from the leaf surface. When the rainy season comes or is irrigated, pathogen spores are spread from the diseased plants to healthy plants as water droplets are washed or splashed, causing disease prevalence. In addition, drying after rain is conducive to the proliferation of conidia and the expansion of the disease, which is likely to cause the epidemic.
The conidial germination of powdery mildew requires a higher temperature, most suitable at 20-25 ° C, and can not be lower than 10 ° C or higher than 30 ° C. The conidia of powdery mildew quickly lose vitality at temperatures above 30 ° C or below -1 ° C. The conidial germination of powdery mildew has a large humidity range. Although the increase of humidity is more conducive to the germination and invasion of conidia, even if the air humidity is reduced to 25%, the conidia can germinate and invade. The host is affected by drought and the occurrence of powdery mildew is more serious. Insufficient fertilization, poor management, lack of water in the soil, untimely irrigation, and insufficient light are all likely to cause plant growth and decline, thereby reducing the resistance to infection by powdery mildew. Excessive watering, excessive nitrogen fertilizer, and increased humidity are also conducive to the occurrence of powdery mildew.
How to prevent melon powdery mildew
1. Choose resistant varieties. The disease resistance of different varieties of melon is significantly different, so the selection of resistant varieties is the key to control the degree of disease occurrence.
2. Clean the countryside. After the crops are harvested, the weeds and residues should be removed in time, the weeds should be removed in time during the growing period of the melons, the diseased leaves should be removed, and the weeds, residues and diseased leaves should be brought to the field for burning.
3. Scientific management to enhance plant disease resistance. Applying the base fertilizer, especially to apply the decomposed organic fertilizer, deep-cut the fine sputum; prevent the plant from prolonging and premature aging, timely tidy up the branches, strengthen the ventilation and light transmission; pay attention to the application of phosphorus and potassium fertilizer in the middle of the growth period, and use the foliar fertilizer to cultivate the robust branches To enhance the disease resistance of the population.
4. Scientific irrigation. Create environmental conditions that are suitable for melon growth and are not conducive to the development of powdery mildew. Irrigation should master four principles: do not pour sunny days on cloudy days, do not pour water in the afternoon, do not pour large water to pour small water, do not pour water to pour dark water (ie under the film).
5. Chemical control. Use 15% powder rusting wettable powder 1000-1500 times liquid, or 40% Dakoning suspension agent 800-1000 times liquid, or 40% Fuxing emulsifiable oil 6000 times liquid, or 10% Shigao high water dispersion granule 2000 times liquid, or 30% Teflon WP 5000 times solution, or 50% thiophanate-methyl WP 1000 times solution alternately sprayed and controlled, sprayed once every 7-10 days, even spray 2-3 times. It is forbidden to use the drug 7 days before harvest for safe harvesting.
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