Symptoms and prevention methods of early and late blight in tomato seedling
Tomatoes mainly harm leaves, stems and fruits. The leaves are damaged, initially appearing dark brown spots, and then enlarged into round to elliptic lesions, with obvious concentric circles, with yellow or yellow-green halos on the edges. Late blight affects tomato seedlings, leaves, stems and fruits. Leaves and green fruits are the most seriously affected. In the seedling stage, the leaves produce pale green water-immersed lesions, white fungus on the edge, and the lesions are brown after enlargement, so that the whole leaves die. And spread to the stem, so that the young stems are water-immersed, contracted, blackened, and the plants collapsed and died.
Autumn 茬 tomatoes are generally planted at the end of July and early August, so the tomato seedling period is due to high temperature and strong light period leading to various problems. In the past few years, the outbreak of tomato TY virus disease has caused heavy losses for vegetable farmers. Now most vegetable farmers have replanted anti-virus varieties, and the occurrence of viral diseases has been alleviated. However, antiviral species are also defective, resistant to viral diseases but not necessarily resistant to other diseases. In addition to viral diseases, the most common diseases in tomato seedling stage are stem-based rot and early and late blight.
First, the symptom identification:
Early blight: dark brown lesions at the base of the stem at the seedling stage, slightly sunken, with a wheel pattern;
Late blight: The seedlings are first infected by leaves, and the leaves are dark green water-stained lesions. The lesions spread from the leaves to the main stems, causing the stems to become thin and dark brown, causing the seedlings to wilting or folding. When the humidity is high, white is produced. Mild layer.
Second, the law and causes:
Early blight is caused by the infection of the fungi of the fungi community. The optimum temperature for the growth and development of pathogens was 26 °C - 28 °C, and the relative humidity of 86% - 98% conidia had the highest germination rate. Condensation on the foliage of vegetables, and the long-term spitting of leaf margins may lead to the prevalence of the disease. Late blight is caused by the infection of Phytophthora infestans in the pseudobacteria. The temperature of 15 ° C - 20 ° C, relative humidity of more than 80% 2 hours, late blight can occur seriously.
Third, prevention methods:
In addition to regulating the shed environment, the key is to prevent pharmacy. It is recommended to spray protective fungicides such as chlorothalonil + mancozeb or chlorpyrifos + chlorothalonil after the three-leaf heart of the seedlings. Once the disease occurs, it is recommended to use a protective and therapeutic agent, such as glacial urea cyanide zinc or metalaxyl manganese zinc. When using copper preparations to prevent early blight in the seedling stage, the dosage should be halved. When the seedling grows up, after entering the adult stage, if the early blight occurs seriously, a fungicide with better therapeutic effect can be selected, such as killing + acephine or difenoconazole + thiabium copper;
The control of late blight can be controlled by ethylphosphorus aluminum + dimethomorph manganese zinc + silver method, but it can not be used in the seedling stage to prevent phytotoxicity.
If the early and late epidemics of tomato seedlings are not treated in time, it is likely to cause heavy losses for the farmers. Therefore, early and late blight of tomato seedlings should be prevented early to control the epidemic.
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