How to identify and control virus disease in stem lettuce? Aphid control is key
Symptoms of stem lettuce virus disease
Stem lettuce virus disease can occur throughout the entire growth period, and the earlier the disease onset, the greater the impact on yield, so early detection and early identification are very important.
Plants infected at the seedling stage generally begin to show symptoms after growing several true leaves: light green and dark green mottling appears on the leaves, and sometimes clear veins can also be seen. The leaves then shrink and become distorted, and growth is clearly abnormal.
When infection occurs at the adult plant stage, the typical manifestation is stunting of the diseased plant. The whole plant cannot grow well, the leaves are irregularly distorted, and its commercial value is greatly reduced.
Where does the virus come from? How is it spread?
The pathogens causing stem lettuce virus disease are mainly two kinds: Lettuce mosaic virus and Cucumber mosaic virus, transmitted through sap contact or by aphids.
The sources of the virus mainly come from virus-carrying lettuce, celtuce, spinach and other crops in nearby vegetable fields. In addition, the seeds themselves may also carry the virus, and such seeds can show disease after emergence.
Field transmission mainly relies on aphids, among which the green peach aphid has the highest virus transmission rate, while the turnip aphid, cotton aphid and euphorbia long-tubed aphid have relatively lower virus transmission rates. In addition, when diseased plants contact and rub against healthy plants, sap can also transmit the virus, so extra attention should be paid during field operations.
The occurrence and spread of the disease are also closely related to weather: when it is hot and dry, there are more aphids, and damage is more severe. Generally speaking, when the average temperature is above 18°C and the field is short of water, the disease spreads very quickly.
Four control measures must be fully implemented
First, choose disease-resistant varieties. This is the least labor-intensive and most basic disease prevention method, and the seed selection must be done well before planting.
Second, when planting in summer and autumn, insect-proof nets, shade nets or plastic film can be used for appropriate shading, which can both block virus-transmitting aphids and reduce disease occurrence.
Third, after emergence, water frequently with a small amount of water, properly control seedling growth, and maintain field moisture supply; once aphids are found, control them in time and keep the virus transmission vector under control.
Fourth, at the early stage of disease onset, apply medication promptly. You can spray 2% ningnanmycin aqueous solution at 500 times dilution, or 24% mixed fatty acid·copper alkali aqueous emulsion at 800 times dilution, to control the spread of the disease.
Overall, prevention of stem lettuce virus disease is more important than treatment. The key points are to cut off the virus source, control aphids, manage water well, and combine this with pesticide control at the early stage of disease onset, so that losses can be minimized.