Control techniques of Brown spot and Black spot of lettuce

Lettuce brown spot and black spot are considered to be mainly harmful to leaves. The leaf spot of brown spot shows two symptoms: one is water-stained at first, then gradually enlarged into round or irregular shape, brown to dark gray spot, ranging from 2mm to 10mm in diameter. Another kind is dark brown disease spot, the edge is irregular, the periphery has the water stain shape halo. Dark gray mildew occurs on the moist spots, and in severe cases, the disease spots merge with each other, until the leaves turn brown and dry. Black spot, also known as ring disease, leaf blight, forms round to nearly round brown spots on the leaves, and the size of the spot varies greatly under different conditions, generally 3mm to 15mm, brown to grayish brown, with concentric wheel lines, and no mildew can be seen in the field. Lettuce is planted annually in Guangdong, these two diseases can spread, spread and infect through seed disease and wind and rain. Generally warm and humid, rainy and foggy for a long time are conducive to the occurrence and prevalence of these two diseases. Insufficient soil fertility, poor growth of lettuce, or excessive application of nitrogen fertilizer will aggravate the disease. The following measures should be taken to control lettuce brown spot and black spot: (1) clean the countryside before soil preparation, apply appropriate amount of lime and sufficient organic base fertilizer after deep drying. (2) during the period of planting management, we should pay attention to rational irrigation, rational combination of nitrogen, phosphorus and potassium with topdressing, and spray foliar fertilizer such as phytoprotegerin, Lufengsu, etc., so as to make the plant grow healthily and improve the resistance. (3) We should pay close attention to spraying before the long seal of lettuce or at the early stage of the disease. the selected agents are: chlorothalonine or chlorothalonil (40% suspension) 600x, chlorozole (50% polysulfide wettable powder) 800g / 1000x, methyl topiramate or propofol (70% ultrafine compound wettable powder) 1000-1500 times, promethazine (50% wettable powder) 1500 times, Xinerpu (65% wettable powder) 400x, Baoning (60% Fuko wettable powder) 600,800 times. Spray once every 7 to 10 days, 2-3 times in a row.