Comprehensive control of cucumber downy mildew in greenhouse
Downy mildew is one of the most common diseases of cucumber grown in greenhouses. Affected by the low temperature and high humidity environment, the disease develops rapidly, and it is easy to damage functional leaves in a short time. In particular, even in cloudy days, the disease is prone to epidemic, and poor control can cause serious losses.
First, the symptoms
Downy mildew mainly damages the leaves of cucumbers and can also harm tendrils, vines and pedicels. At the beginning of the disease, water-stained transparent dots formed on the back of the leaves. Afterwards, the lesions gradually expanded. Due to the limitations of the veins, they were polygonal and water-stained. When wet, there is a layer of black mold on the lesion. The early lesions of the leaves were yellow in color and their edges were not obvious, and they turned yellow-brown afterwards. In severe cases, the lesions are contiguous, the whole leaf is curled and dried, and only the heart is left. After the occurrence of a central diseased plant, the disease became rapidly prevalent at temperatures of 16°C to 22°C and a humidity of 85% or more, and the disease generally became common after 15 to 20 days. Under the conditions of air drying or temperatures above 30°C, the disease development is limited and the incidence is lighter. In addition, extensive management, insufficient water or excessive dense planting, long-term accumulation of water, and field closure can easily induce the disease to occur.
Second, control methods
1. Scientific fertilization. Fertilization should be dominated by organic fertilizer, combined organic and inorganic, combined application of nitrogen, phosphorus, and potassium fertilizers to improve the growth environment of cucumber, fitness training, improve plant disease resistance.
2. Watering time should be appropriate. Watering on a sunny morning or in the morning, pouring it to a closed shed and raising the temperature to 33°C, and let it stand for 1 hour before letting go.
3. Control humidity and temperature. The daytime temperature is maintained at 25°C-30°C. When it is higher than 31°C, the air should be released. The top wind must be opened first. The night temperature is maintained at 11°C-13°C. The relative humidity during the day is maintained at 75%-80%, which is beneficial to cucumber photosynthesis. Relative humidity at night maintains 80%-85%, which can reduce nutrient consumption and inhibit the invasion of bacteria.
4. High temperature stuffy shed. After the onset of cucumber downy mildew disease can be used high temperature sterilization, according to the weather forecast, choose to continue for more than 2 days of sunny days, the first day of the main vine growth points fall to prevent roasting plants, and then watering. 10 o'clock the next day stuffy shed, the temperature inside the shed reached 45 °C -46 °C (too high shade), 90-120 minutes after the gradual release of air cooling, and finally controlled at 25 °C -28 °C, this can not only kill the downy mildew The bacteria can control the melons. Adding foliar fertilizer after stuffy shed, the effect is better.
5. Leaf spray sugar. In the late growth stage of cucumber, 1% urea solution and the same amount of white sugar solution can be sprayed in the morning, sprayed once every 5 days, and sprayed four times in total, paying attention to the back of the leaf.
6. Clear the source of the disease. For disease-causing greenhouses, the diseased plants should be cleared in time, brought out of the shed to burn, and reduce the repeated infection of pathogens.
7. Chemical control. Preventive control before the onset of disease can use Dasheng M-45 wettable powder 800 times liquid (mu of 125 grams), 40% of Kokoning suspension 600 times liquid (mu of 165 grams) or 77% to kill WP 1000 Double fluid (100 grams per mu) spray.
When the disease enters the initial stage, when the dew is not dry in the early morning, after seeing the water-soaked central diseased plant for 5-7 days or after a large number of water-soaked lesions have occurred for 1-2 days, the lesions of the leaves develop from flooding to Polygonal, frosty layer on the back of the leaf is the control period. 72% Kelu wettable powder 1000 times liquid (100 g/mu), 69% Ankang zinc wettable powder 1000 times liquid (100 g/mu), 58% radomeril-manganese zinc wettable powder 1000 times Liquid (100 grams of mu) or 72.2% Prec 800 times alternating spray control, medication interval of 7-10 days, continuous spray 3-5 times. Severe disease field development as the disease, if necessary, can also increase the number of spraying.
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