First, the symptoms
It is mainly harmful to the leaves. At the beginning of the disease, it appears orange-red near-circular dots on the leaves, and then expands into near-circular or irregular-shaped orange-red to dark brown necrotic spots, slightly depressed, and is easily broken and perforated in the later stage. The lesion or multiple lesions fuse, causing the leaves to dry up. The pathogen is called Pseudomonas fluorescens biotype II bacteria, belonging to the bacterial border of the thin wall bacteria. Routes of transmission and pathogenesis: The bacteria will overwinter with the diseased or contaminated seeds. When the conditions are appropriate, they will invade from the stomata, water holes or wounds of the long-leaf lettuce leaves, and form systemic infections, relying on the seeds and rainwater or insects and fertilizers. Spreading and spreading, high temperature and high humidity are beneficial to the disease. The suitable temperature is 25 °C ~ 26 °C, the highest is 38 °C, the terrain is low, the soil is sticky or the moisture is retained.
Second, prevention and treatment methods
　　 1, for 2 to 3 rings and cereal crops, seeds before sowing seeds 0.3% by weight of 47% copper oxychloride wettable powder dressing Jubilee.
　　 2. Apply bio-organic fertilizer or decomposed organic compost.
　　 3 , strengthen management, timely drainage after the rain, the protection of the ground should pay special attention to ventilation and moisture, to prevent excessive humidity for a long time.
　　 4 , at the beginning of the disease, spraying 20% thiabend copper suspension 600 times solution or 47% spring oxychloride copper WP 700 times solution, 20% leaf cumin 800 times solution, the effect is obvious.
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