One of cucumber diseases in summer how to control cucumber downy mildew

Downy mildew, commonly known as "horse running dry" and "black hair", is one of the main diseases of cucumber in summer. It has the advantages of fierce coming, rapid spread and serious damage, which can kill almost the whole leaf of cucumber in one or two weeks, and seriously affect the yield of cucumber. So how to control cucumber downy mildew?

Cucumber downy mildew

Symptom characteristics

The disease began from the lower leaves of cucumber plants, and many light green watery spots grew on the edge of the leaves, and then developed into large yellow-green to yellow spots, which were polygonal due to the limitation of leaf veins. In the morning or when the cucumber leaf surface is covered with water, the disease spot shows a dark green water stain. Under moist conditions, the back of cucumber leaves infected with downy mildew formed purple-brown or dark-brown irregular spots, with downy mildew on the surface. In severe cases, the disease spots fused, the leaves turned dark brown, the edges rolled up, and the cucumber leaves withered and died from the bottom up.

Morbidity regularity

The disease is an airborne fungal disease caused by pseudo-downy mildew in Cuba. As long as the temperature is 16-20 ℃ and the relative humidity is above 85%, the disease can occur. The optimum temperature for the onset of downy mildew is 20-26 ℃. Cucumber leaf dew or water film is a necessary condition for downy mildew infection. During infection, the spores produced by sporangia, germinating bud tube, or sporangium germinating bud tube directly invaded through the epidermis of cucumber leaves, causing the epidemic of the disease. The occurrence and prevalence of cucumber downy mildew can be caused by cold or hot climate, humid air and large temperature difference between day and night.

Prevention and cure method

1. Agricultural prevention and control. Disease-resistant varieties were selected, such as Jinza 1, 2, 3, 4, Xiafeng 1, Jicai 2, Zhongnong 1101 and so on. The key to cucumber cultivation and management is to control water, water small water frequently, and pay attention to ventilation and dehumidification. Applying sufficient base fertilizer and adding phosphorus and potassium fertilizer is beneficial to enhance the disease resistance of cucumber plants. Reasonable arrangement of cucumber planting density, timely removal of old and diseased leaves, ventilation and light transmission in the field and reduction of moisture in the field can reduce the occurrence and spread of downy mildew. The high temperature method can be used to close the greenhouse for 2 hours at noon to make the upper temperature of cucumber plant reach 44-46 ℃, which can kill a part of downy mildew in the greenhouse and be stuffy once every 7 days.

two。 Chemical control. Give priority to prevention, when there is no downy mildew, it is necessary to spray prevention. When a disease occurs, it is necessary to spray immediately to prevent and cure the disease. the commonly used agents are 58% metalaxyl ·mn-Zn wettable powder 500 times, 64% poison alum 500 times, 72.2% Pulic water 800 times, 80% triethyl aluminum phosphate (ethyl aluminum phosphate, plague) 600 times, 70% ethyl phosphate aluminum manganese zinc wettable powder 500 times, 72% urea manganese zinc wettable powder 700 times, DuPont Kelu 800 times Spray once every 7-8 days, according to the condition of cucumber downy mildew to determine the number of spraying. In order to prevent cucumbers from developing drug resistance, the above pesticides should be used alternately.