Lettuce brown spot and black spot disease are mainly damage leaves. The leaf spot of brown spot shows two symptoms: one is a watery spot at the beginning, and then gradually expands to a round or irregular shape, brown to dark gray spot, ranging from 2-10 mm in diameter. The other is a dark brown lesion with irregular edges and a watery halo around the periphery. Dark, dampish moulds were found on wet surfaces. In severe cases, the lesions merged and the leaves became brown and dry. Black spot, also known as rotenia and leaf blight, forms round to near-circular brown spots on the leaves. The spot size varies widely under different conditions. Generally, it is 3-15 mm, brown to grayish brown, and concentric ring patterns. Fields can't see mildew.
The following measures should be taken to prevent brown spot and black spot of lettuce: (1) Before gardening, clean the pastoral area, deepen the ground and apply lime and organic base fertilizer. (2) Pay attention to reasonable irrigation during planting and management period, and use N, P and K with reasonable top dressing and spray foliar fertilizers such as phytoalexin and chlorophyllin to make the plants grow robustly and increase their resistance. (3) Spraying should be stepped up before the start of sealing of raw lettuce or at the early stage of disease. The selected agents are: Baifening or chlorothalonil (40% suspension) 600 times, chlortetrazol (50% polysulfide WP 800-1000 times, 1000-1500 times of thiophanate or pumic (70% ultrafine compound wettable powder), 1500 times of acetaminophen (50% wettable powder), Xinpu (65% wettable) Powder 400 times, Baoning (60% Duofu WP) 600-800 times. Spray once every 7-10 days for 2-3 consecutive times.
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