How to prevent watermelon leaf blight, and what are the symptoms?

Watermelon leaf blight is an increasingly serious leaf disease in watermelon in recent years, which occurs in all growth stages of watermelon. Cotyledon disease, mostly in the leaf edge water stains, and then turn into light brown to brown, round or semi-circular water stains, when the humidity is high, it spreads to the whole cotyledon and dries up. When true leaves are infected, obvious waterlogging spots appear on the back of leaves or between veins. When the humidity is high, the leaves will lose water and wither. When the weather is clear and the temperature is high, it is easy to form 2 ~ 3 mm round to nearly round brown spots on the whole leaves, and then merge into large spots, and the diseased parts will become thinner, forming leaf blight. The stems and vines are infected, producing spindle-shaped or oval slightly concave brown spots. When the fruit is infected, there are slightly convex round brown pits on the fruit, which can penetrate deep into the pulp and cause the fruit to rot. When the humidity is high, the disease grows a gray-black to black mold layer, which is the fruiting body of the pathogen (color map 13).

Prevention and control methods:

(1) Establish a disease-free Taneda and select disease-resistant varieties suitable for local cultivation. At present, the varieties with good resistance are Zhengzhou No.5, Zhengza No.7, Xinong No.8, Yueyou No.2, Fuzhou Watermelon, Xinhongbao and so on.

(2) After harvesting, pay attention to clear the sick and disabled bodies, bury or burn them in a centralized way, and do not pile the sick and disabled bodies on the edge of the field.

(3) Adopting formula fertilization technology, applying compost fermented by enzyme bacteria to avoid excessive application of nitrogen fertilizer, and spraying Huimanfeng liquid fertilizer, with 2320 ml of water every 667 m, 500 times, to improve disease resistance.

(4) Scientifically determine the sowing date. In the open field, when the average temperature of the day is stable above 15℃ and the soil temperature at a depth of 5 cm is stable above 12℃, it is appropriate to sow watermelon when the peach blossoms bloom. If you want to grab early, you can cover it with plastic film to make it reach the above temperature before sowing.

(5) Soak the seeds with 75% chlorothalonil wettable powder or 50% chlorpheniramine wettable powder in 1000 times solution for 2 hours, and then accelerate germination and sowing after washing.

(6) Rain-proof cultivation methods should be advocated when conditions permit, and special attention should be paid to ditching and drainage of open-field watermelons after rain to prevent water retention, which plays an important role in alleviating diseases.

(7) Strengthen the forecast, and know that 50% Sukeling WP 1500 times or 50% chlorpheniramine WP 1000 times, 40% chlorothalonil SC 500 times, 70% mancozeb WP or dry SC 500 times and 80% Sheng Da WP 600 times should be sprayed before the onset.

(8) The trellis cultivation method is adopted, with 265,438+0,500 plants per 667 meters, one vine is pruned, the first female flower is picked when the leaves are 6-7, and 65,438+02-65,438+03 leaves are left, which not only increases production and income, but also alleviates diseases.

(9) It is recommended to apply 10% Baolifeng watermelon swelling-reducing and sweetening treasure, with 10 ~ 15 kg of water per branch, once every 10 day 1 time, twice in a row.