There are few diseases in lettuce, but there are also common disease causes and prevention and treatment methods.

Lettuce is one of the common dishes in daily life. Although there are few diseases, they still occur. There are three common diseases, which should be controlled in time.

Lettuce downy mildew

Downy mildew:

1. Symptomatic characteristics. First harm to the old leaves, chlorosis or yellowish disease spots appear on the front of the leaves, the disease spots gradually expand with the development of the disease, but do not cross the leaf veins, the shape and size are different, and the healthy parts of lettuce are yellow and green alternately. A layer of white mildew was formed on the back of the disease spot, and soon the leaves yellowed and withered.

two。 Prevention and control methods. ① soil treatment. Sprinkle lettuce rhizosphere soil with 5% formalin, or garden soil with 2% lime powder mixed with sterile mud powder. ② seeds were sterilized. Before sowing, 35% metalaxyl seed mixture with a seed weight of 0.1% was used to reduce the source of primary infection. ③ field management and protection. In the early stage of the disease, the humidity in the field was reduced, the residual plants of diseased leaves were removed, the stagnant water was prevented, and the field was ventilated and transparent. The rhizosphere soil can be drenched with 5% formalin solution. After harvest, clear the garden in time and take the diseased parts of lettuce outside the garden to be buried or burned. ④ chemical control. Before application, the diseased leaves must be removed, and after the central diseased plant is found, start spraying 75% chlorothalonil wettable powder 500 times, 72.2% Prik water 600-800 times, 64% poison alum wettable powder 500 times or 58% Redomir wettable powder 800 times, spray once every 7-10 days, 2-3 times in a row.

Lettuce Botrytis cinerea

Grey mold:

1. Symptomatic characteristics. Infected at the seedling stage, the injured stems and leaves showed water-immersed rot. The adult plant infected with the disease began with the leaves near the surface, showed water immersion at first, and then expanded rapidly. The stem base is rotten and the sore surface has a grayish brown mildew layer. When the weather is dry, the diseased plant gradually dies, and the mildew layer changes from white to green; when the humidity is high, it fester upward from the base, and the petiole is dark brown.

two。 Prevention and control methods. ① fertilized reasonably to avoid high humidity in the field and enhance disease resistance. ② removed the old leaves of lettuce to improve ventilation conditions, strengthen ventilation and reduce diseases. ③ chemical control. At the initial stage of the disease, 50% carbendazim wettable powder 1000 times, 50% methyl thiophanate wettable powder 1000-1300 times, or 50% carbendazim 1200-1500 times were sprayed. Depending on the condition, the drugs should be used in rotation every 7-10 days, and the drugs should be prevented and treated continuously for 2-3 times. Stop using medicine 15 days before harvest. Smoke in ④ shed. Smoke with 40% chlorothalonil (chlorothalonil and promethrin), 40% chlorothalonil (chlorothalonil and trimethoprim) or 15% promethrin, once every 7 days for 2-3 times. After ⑤ harvest, deal with the disease and residue in time, burn it or bury it deeply, prevent the spread of bacteria in the field, and dig deep in time to reduce the source of bacteria.

Black rot of lettuce

Black rot:

1. Symptomatic characteristics. The main harm to the leaves, mostly from the petiole, leaf main vein began to occur, initially showing a light brown wet rot-like short stripes, and then along the vascular bundle extended to the main veins and reticular veins, showing purple-black lesions, and finally the leaves dried up. When moist, the spot surface exudates the bacterial pus, faintly visible, touches it has the sticky feeling, this is the characteristic of this disease.

two。 Prevention and control methods. ① implements crop rotation, strengthens fertilizer and water management, removes field weeds in time, and pays attention to field hygiene. ② seed selection and seed dressing. In areas where vegetable black rot often occurs, disease-resistant varieties are selected and seeds are mixed with 50%DT wettable powder before sowing (the dosage is 0.4% of the seed weight). In the early stage of ③, spray as early as possible. 72% agricultural streptomycin 3000 times, 47% Garinon wettable powder 400,600 times or 58.3% can kill 2000 dry suspension 600,800 times, spray once every 7-15 days, spray 2-3 times according to the condition, and use drugs alternately. When spraying, you can also add pesticides, such as chrysanthemum and horse EC 2500 times liquid, mixed spraying, disease and insect treatment.