Lettuce pests and their prevention

Lettuce is one of the main vegetables in Tonghai. It enjoys cool and cool weather, short days and wide adaptability. Its main pests and diseases are:
1. Downy Mildew: A fungal disease. The lettuce stem is parasitism. The incidence of adult plants is the most important. It mainly damages the leaves. The near-ground leaves firstly develop. The sick leaves produce light yellow near-circular or polygonal spots. At the time of growth, the leaves grew white and yellow, and later lesions turned yellow-brown, and many lesions were connected together to make the leaves dry. Bacteria can overwinter on seeds, soil and diseased plants. They can be transmitted through air currents, rainwater, irrigation and insects under conditions of low temperature and high humidity. The density of fields, poor drainage, and wet ground are often serious. Control method: Use 30% thiram mold dressing or 25% metalaxyl wettable powder dressing, 70% chlorothalonil 700 times or 72% WP wettable powder 800 times or 50% Anke Manganese Zinc WP 500 times a week sprayed continuously sprayed 2-3 times.
2. Black rot: leaf spot and yellow veins are caused after the onset of adult plants. The leaf spot develops into a "V"-shaped brown spot inward from the leaf margin. The veins become necrotic and black, the stem and roots are damaged, and the vascular bundles become dark. . The prevention and control method is as follows: 200 units of agricultural streptomycin, 65% of mancozeb 600 times liquid, and 50% DT300 times of liquid.
3, Sclerotinia: pay attention to crop rotation, reasonable dense planting, watering should not be too much, the early onset of spraying 1:1:200 Bordeaux liquid or 1000 times Vincythromycin nuclear control.
4. Soft rot: Control with 1000 times enemy cough or 200 units of agricultural streptomycin.
5. Insect pests: There are locusts, thrips and tigers. Control methods: Aphids and thrips can be sprayed with 75% dimethoate emulsion 1000 times. The control tigers were watered with 90% trichlorfon 800 times.

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