Control methods of watermelon blight

Watermelon blight is a kind of soil-borne disease of high temperature and humidity, also known as watermelon Phytophthora, dead seedlings, etc., which occurs all over the country, and the damage is aggravated year by year. The disease is more serious in the south than in the north, especially in rainy years during the watermelon growing period. Besides watermelons, it also harms melons and other melon crops. Let's take a look at the prevention and control methods of watermelon blight.

Hazard characteristics

Watermelon blight generally affects the root neck of melon, as well as leaves, vines and fruits. Dark green watery spots appeared in the root and neck at the initial stage of the disease, and the disease spots developed rapidly around the stem base in the form of soft rot, constriction, wilting and death of the whole plant, the leaf was in the shape of wilt, and the vascular bundle did not change color. When the disease occurs, the leaves produce dark green watery spots, and rapidly expand into near-round or irregular large yellowish-brown spots, the whole leaves rot when the humidity is high, and the diseased leaves are light brown and easily broken after drying. When the stem was killed, it showed a water-stained dark green spindle-shaped depression, and died above the diseased part. The damage to the fruit showed a water-stained dark green round depression, which quickly spread to the whole fruit surface, the fruit was soft rotten, and a thin layer of white mildew grew on the surface of the disease spot.

Occurrence regularity

The pathogen of watermelon blight preferred the environment of high temperature and high humidity, and the optimum temperature was 28 ~ 30 ℃, and the disease was inhibited when it was lower than 15 ℃. Under the condition of suitable temperature, the morning and evening of the rainy season, rainfall and the number of days of rainfall are the decisive factors of the disease and epidemic degree. The peak of illness in the field is immediately after the peak of rainfall. After the appearance of the central diseased plant, if the daily rainfall is more than 50 mm or the ten-day rainfall is more than 100 mm, the disease develops rapidly and is easy to become epidemic. If there is no rain and no watering for more than 10 days, the disease will stop spreading. Under the condition of high temperature and humidity in the rainy season, the drainage and ventilation is poor, the planting is too dense, and the disease is serious. The disease is aggravated by low-lying terrain, poor drainage, uneven border surface, prone to stagnant water and continuous cropping for many years, as well as too much watering, too dense planting, too much nitrogen fertilizer or bacteria-carrying fertilizer.

Prevention and cure method

1. Variety selection: among the more than 60 watermelon varieties introduced in China in recent years, Xiang Watermelon No. 3, No. 4 and No. 6 showed resistance to blight, Hunan Qin seedless watermelon, Qiongxue, Qinghongbao and so on. As for some varieties with strong disease resistance, such as Jingxin No. 1, Zhengza No. 5, Xinhongbao, Jinhuabao, Tezao Jialong, Yunzhong No. 1, Changmi No. 1 and No. 2, Zhongyu No. 1, Xiabao No. 3, Bafengshou No. 3, Qiongshui and so on, whether they are also resistant to blight remains to be further observed and identified.

2. Agricultural prevention and control: crop rotation with non-melon crops for more than 3 years, cleaning the countryside, cutting off the source of infection of overwintering pathogens, timely uprooting of diseased plants, concentrated deep burial or burning, without unrotten organic fertilizer with diseased remains. Reasonable close planting, deep ditch and high border cultivation, timely drainage after rain, control of field humidity. Watermelons cultivated in protected facilities should be irrigated with small water or drip irrigation under plastic film to save water and heat preservation so as to reduce the humidity in the greenhouse. Flood irrigation or series irrigation is strictly prohibited.

3, medicament prevention: before sowing, soak the seeds in 55 ℃ warm water for 15 minutes, dry and sow the seeds or accelerate the germination, or mix the seeds with 500g of 20% methyl fumarate EC 500g / 100kg. Before the onset of the disease, you can use flumiramine (silver farfarin) wettable powder 600x, or 70% propiconium zinc (Antaisheng) wettable powder 40000x liquid, or 60% pyrazolyl ester Dysenlian (Baitai) 1200 times liquid, or 70% Dysenlian (Pinrun) 700x solution to fill the root or spray.

4. Chemical control: spray 72% urea manganese zinc (Kellol) wettable powder 700x, or 50% dienylmorpholine (Anke) wettable powder 2500 times, or 25% dialkynyl amides (Ruifan) 2500 times, 70% ethyl phosphate aluminum manganese zinc wettable powder 500x, 72.2% aldicarb hydrochloride (Prike, recycled) water solution, 58% metalaxyl% manganese zinc (Jinlei) wettable powder 500x 64% Manganese Zinc (disinfectant alum) wettable powder 500 times liquid, once every 7-10 days, continuous prevention and treatment for 3 times. If necessary, the above fungicides can also be used to irrigate the roots, and the mixed solution of each plant is 0.25 to 0.4 litres. if spraying and root irrigation can be carried out at the same time, the control effect will be obviously improved.