Control methods of severe leaf withered stem rot celery spot blight with long and small black spots

Celery spot blight, also known as late blight, leaf spot, commonly known as "fire dragon", is a common disease of celery in greenhouse, affecting the yield and quality of celery. In deep winter, low temperature and high humidity are often beneficial to the occurrence and spread of celery spot blight. The symptoms and control methods of celery spot blight are as follows.

Celery spot blight

First, symptoms. Celery spot blight mainly harms leaves, followed by petiole and stem. Old leaves get sick first, from the outside to the inside. The disease spot is light brown oil immersed spot at first, the edge is obvious, and then develops into irregular disease spot, the color changes from light yellow to gray, the edge is dark reddish brown, and accumulates small black grains, and there is often a yellow halo ring outside the disease spot. Petiole, stem spot brown, oblong slightly sunken, scattered black spots in the middle, serious, withered leaves and stems rotten.

Second, the law of the disease. Celery spot blight is a fungal disease, low temperature and high humidity is conducive to the occurrence of the disease, the disease occurs at an appropriate temperature of 20: 25 ℃, humidity of more than 95%, in the deep winter, even cloudy days, frequent temperature fluctuations, daytime dry heat, night dew, celery growth is weak, irrigation is more, ventilation and moisture drainage is not timely can often lead to the spread of the disease. 

Third, prevention and control methods.

1. Balanced fertilization. To apply sufficient base fertilizer and mature organic fertilizer, topdressing and increasing phosphorus and potassium fertilizer, controlling the amount of nitrogen fertilizer, foliar fertilizer and micro-fertilizer can be sprayed to enhance the resistance of celery.

2. Cooling and dehumidification. When the daytime temperature is controlled at 15: 20 ℃, when the temperature is more than 20 ℃, the air should be released in time, and at night it should be controlled at 10: 15 ℃ to reduce the temperature difference between day and night, reduce condensation, and do not flood.

3. Chemical control. Fumigate the shed with 45% chlorothalonil smoke remover, 150 grams per mu, light it in 5-6 places, and fumigate for 1 night, once every 10 days. In the early stage of the disease, spraying 70% mancozeb wettable powder 600 times, or 50% carbendazim wettable powder 600 times 800 times, once every 7 to 10 days, continuously spraying 2 times for 3 times, the control effect is obvious.

4. Clear the diseased plant. For the sick shed, the remnants of indoor celery should be removed in time to reduce the spread and spread of bacteria.