It is a kind of fungal disease, which is located in the middle and upper leaves of cucumber. At about 8:00 a.m. every day, check whether there are water soaked, polygonal spots on the back of the leaves, and whether there is gray mold layer on the spots. If there are these three points, it can be diagnosed as downy mildew.
The suitable environment is 16 ℃ ~ 22 ℃ and the relative humidity is over 83%. There are two fears of the pathogen, that is, to be afraid of dryness and high temperature. The pathogen died naturally 3-5 days after drying. In the case of high humidity in the shed, the temperature can be controlled to 45 ℃ for 2 hours. It is easy to control the disease by spraying appropriate chemicals.
Chemical control: Anke, pulik, Mieke, frost urea manganese zinc, yikuaijin, jinredomir and amixida can be selected. In addition, in the prevention and control of downy mildew, attention should be paid to the simultaneous occurrence of bacterial keratosis, which can be added to the fungicides for the prevention and control of downy mildew.
Symptoms: dangerous to melon, leaves and stems. Disease caused by fungal infection.
The temperature is about 20 ℃, the light is insufficient in cloudy days, the relative humidity is over 90%, and the condensation time is long, which is the important condition for the occurrence and spread of gray mould. If the temperature is higher than 30 ℃ and the relative humidity is below 90%, the disease will stop spreading.
Medicament control: use 1500 times of 50% puhaiyin wettable powder, once every 6-7 days, for 3-4 times in a row, and spray the medicament on the flowers and young melons.
Symptoms: first, small round white powdery mildew spots grow on the front or back of the lower leaves, gradually expand, thick and dense, and soon become a piece.
In the late stage of the disease, the whole leaf was covered with white powder, then turned gray white, and finally the leaf was yellow brown and dry. The stem and petiole also have the similar disease spot with the leaf, dense white powdery mildew spot.
Control method: choose 1000 times of 20% Triadimefon wettable powder or 500-600 times of 75% dakinin wettable powder, or 2500 times of 10% Shigao, or 400 times of 2% rice, spray once every 5-7 days.
Symptoms: the round or oval water soaked spots on the cotyledons at seedling stage are slightly sunken, then brown and wither. At the stage of plant formation, the size of the primary needle on the leaf is water soaked, and the expansion of the disease spot is restricted by the vein. When the humidity is high, the disease spot on the back of the leaf produces milky mucus, which forms a layer of white film or white powder after drying. The disease spot is brittle and easy to perforation in the later stage.
Control methods: spray 5000 times of new phytomycin, 500 times of 30% copper succinate (DT) wettable powder, or 400 times of 77% wettable powder.
