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Tomato late blight prevention
Symptoms identify seedlings, leaves, stems and fruits that can be affected. When the seedlings are infected, the lesions spread from the leaves to the main stem, making the stems thin and dark brown, causing the whole plant to smash or fold. When the humidity is high, the surface of the disease is white mold; the leaves of the adult stage are infected, mostly from the lower leaves of the plants. The tip or leaf edge begins to develop, initially a light green irregular shape lesion, which turns brown after expansion. In high-humidity, water-soaked, white mold on the junction of the leaf-back disease, the disease on the stem, the lesion is dark brown, when the stem is still young, there will be obvious contracture, and cause the plant to wilting; fruit disease It mainly occurs in green fruit. The disease spot is oily and dark green at the beginning, and then becomes dark brown and brownish. It is slightly sunken, the edges are obvious, the moiré is irregular, the fruit is generally not soft, and when the humidity is large, it grows a small amount of white. Mildew, quickly decays. The disease is easily confused with early blight, and can be distinguished by moisturizing methods. For example, people with white mold in the diseased department are late blight. Those with black mold are early blight.
The pathogen is caused by Phytophthorainfestans (Mont.) deBary (the Phytophthora infestans), which belongs to the genus Hymenoptera. Hyphae branches, colorless, no septum, thin, multi-nuclear. Cysts are colorless, single or multiple bundles, extending from the stomata; cysts are slightly thinner than hyphae, nodular enlargement on branches, size 624-1136μm × 627-746μm. Sporocysts terminal or lateral, ovate or suborbicular, colorless, apically sessate, sessately sessately sessately sessately sessate sessate sessate sessate sessate sessate sessate sessate sess. . Ovoids are rare.
Regular pathogens sometimes overwinter with oospores, but are rare. The mycelial development temperature is 24 ° C, the highest is 30 ° C, the lowest is 10-13 ° C. The sporangia formed a temperature limit of 3-36 ° C, the relative humidity was higher than 91%; 18-22 ° C, the relative humidity of 100% was the most suitable. Sporangia germination is closely related to temperature. It takes 3 hours at 10 °C, 2 hours at 15 °C, and 1.5 hours at 20-25 °C. This bacterium can damage tomato and potato, and differentiate into different pathogenic groups. Generally, the strong pathogenic group on tomato is also highly pathogenic to potato. Although potato late pathogens are weak in pathogenicity to tomato, pathogenicity can be improved after multiple infestation of tomatoes.
Prevention and treatment method
(1) Planting disease-resistant varieties, such as: Zhongshu No. 4, Zhongshu No. 5, Yuanhong, Qihong No. 2, Jiahong, Zhongza No. 4 and other varieties are more resistant to disease and may be considered for selection.
(2) Rotating with non-solanaceae crops for more than 3 years, rationally close planting, using formula fertilization technology, strengthening field management, and snoring.
(3) Protecting the tomato from the seedling stage, pay attention to controlling the ecological conditions, pay attention to the wind and reduce the relative humidity of the greenhouse under the premise of ensuring the temperature.
(4) Chemical control. It was found that the central diseased plants were sprayed after removing the diseased leaves. The available agents were: 72. 2% Plex aqueous solution 800 times solution, 72% Anke manganese zinc wettable powder 600 times solution, 72% Anke manganese zinc wettable powder. 1000 times liquid, 40% nail cream copper wettable powder 700-800 times liquid, 64% antivirus 矾 wettable powder 500 times liquid, 70% ethyl phosphine? manganese zinc wettable powder 500 times liquid, generally used for 667 square meters A good liquid 50-60L, once every 7-10d, continuous control 4-5 times. Can also be used 50% nail cream copper wettable powder 600 times liquid, or 60% amber ethyl phosphine aluminum wettable powder 400 times liquid root irrigation, each plant infusion liquid 0.3 liters, every 10d or so, continuous infusion 3 times. The protective ground is prevented by the dust method and the smoke method, that is, 45% of chlorothalonil agent is applied per 667 square meters, and 5% of chlorothalonil dust is 1 kg per 667 square meters, once every 9 days.
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