Curled, twisted and stunted leaves on stem lettuce? Virus disease control methods

    Stem lettuce virus disease can occur throughout the entire growth period, and when it occurs early, it has a major impact on yield. Infection at the seedling stage: symptoms appear after several true leaves have formed, with light green and dark green mottling on the leaves. Sometimes vein clearing appears, and the leaves become curled and twisted. When infected at the mature plant stage, the plants become stunted and the leaves twist irregularly. The main pathogens of stem lettuce virus disease are Lettuce mosaic virus and Cucumber mosaic virus, which are transmitted by sap contact or by aphids. 

Stem lettuce virus disease

    The sources of stem lettuce virus disease come from virus-carrying lettuce, celtuce, spinach and other crops in nearby vegetable fields. Seeds can also carry the virus, and symptoms appear as soon as the seedlings emerge. Field spread depends mainly on aphids, and sap also transmits the virus when diseased and healthy plants touch and rub against each other. The green peach aphid has the highest transmission rate, while the turnip aphid, melon aphid and greater black-backed aphid have lower transmission rates. The occurrence and spread of stem lettuce virus disease are related to weather; under high temperature and drought, aphids are abundant and damage is severe. Generally, when the average temperature is above 18°C and the field lacks water, the disease spreads very quickly. 

    Control methods:

   (1) Choose disease-resistant varieties. 

   (2) When planting in summer and autumn, using insect-proof netting, shade netting or plastic film for appropriate shading can reduce disease occurrence.

   (3) After emergence, irrigate frequently with small amounts of water, subject the seedlings to appropriate controlled water stress, and control aphids promptly when found. 

   (4) In the early stage of the disease in stem lettuce, spray 2% Ningnanmycin aqueous solution at 500 times dilution or 24% mixed fatty acid·alkaline copper emulsion at 800 times dilution.