A Detailed Guide to the Latest Control Methods for Watermelon Blight
Watermelon blight is a high-temperature, high-humidity soil-borne disease, also known as watermelon Phytophthora blight, dead vines, etc. It occurs throughout the country, and the damage is increasing year by year. The disease is more severe in the south than in the north, and is especially severe in rainy years during the watermelon growing period. Besides watermelon, it also harms melon and other cucurbit crops. Let's take a look at the control methods for watermelon blight!
Damage Characteristics
Watermelon blight generally attacks the root crown of the plant, and can also attack the leaves, vines and fruit. In the early stage of the disease at the root crown, dark green water-soaked lesions appear, which rapidly expand to encircle the stem base, becoming soft-rotten, constricted, and causing the whole plant to wilt and die, with leaves showing a green wilt, while the vascular bundles do not discolor. When the leaves are affected, dark green water-soaked spots appear and rapidly expand into nearly round or irregular large yellowish-brown lesions; under high humidity the entire leaf rots, and when dry the diseased leaves turn light brown and are very easily broken. When the stem is attacked, it shows water-soaked dark green spindle-shaped depressions, and the part above the diseased area dies. When the fruit is affected, it shows water-soaked dark green round depressions that rapidly spread over the entire fruit surface, the fruit becomes soft-rotten, and a sparse layer of white mold grows on the surface of the lesions.
Occurrence Pattern
The pathogen of watermelon blight prefers high temperature and high humidity environments. The optimum temperature for disease development is 28-30°C, and below 15°C the disease is inhibited. Under suitable temperature conditions, the timing of the rainy season, the amount of rainfall, and the number of rainy days are the determining factors for the occurrence and epidemic level of the disease. The peak of disease occurrence in the field usually follows immediately after the peak of rainfall. After the appearance of the first diseased plants, if the daily rainfall reaches more than 50 mm or the ten-day rainfall exceeds 100 mm, the disease develops rapidly and is prone to becoming an epidemic. If there is no rain for more than 10 days and no watering is done, the disease stops spreading. Under high temperature and high humidity conditions in the rainy season, poor drainage and ventilation, and overly dense planting, the disease is severe. Low-lying terrain, poor drainage, uneven bed surfaces, plots prone to water accumulation and continuous cropping for many years, as well as excessive watering, overly dense planting, excessive application of nitrogen fertilizer or application of contaminated fertilizer, all aggravate the disease.
Control Methods
1. Variety selection: Among the more than 60 watermelon varieties promoted in China in recent years, those showing resistance or tolerance to blight include Xiang Watermelon No. 3, No. 4 and No. 6, Hunan Qin Seedless Watermelon, Qiongxue, Qinghongbao, etc. As for some varieties that generally show relatively strong disease resistance, such as Jingxin No. 1, Zhengza No. 5, Xin Hongbao, Jinhuabao, Tezaojialong, Yunzhong No. 1, Changmi No. 1 and No. 2, Zhongyu No. 1, Xiabao No. 3, Bafengshou No. 3, Qiongsu, etc., whether they are also resistant to blight remains to be further observed and identified in various regions.
2. Agricultural control: Carry out crop rotation with non-cucurbit crops for more than 3 years, clean the field, cut off the source of overwintering pathogen infection, promptly pull out diseased plants, and bury them deep or burn them in a centralized manner. Do not use undecomposed organic fertilizer containing diseased plant residues. Reasonably dense planting, deep furrow and high bed cultivation, timely drainage after rain, and control of field humidity. For watermelon grown under protected cultivation, small amounts of water should be applied by subsurface seepage irrigation under film or by drip irrigation, saving water and maintaining temperature, so as to help reduce the humidity in the greenhouse. Flood irrigation and sequential irrigation are strictly prohibited.
3. Chemical prevention: Before sowing, soak the seeds in warm water at 55°C for 15 minutes, then dry them and sow or sow after germination, or mix 500-700 g of 20% tolclofos-methyl emulsifiable concentrate with 100 kg of seeds. Before the disease occurs, use fluopicolide propamocarb (Infinito) wettable powder at 600 times, or 70% propineb (Antracol) wettable powder at 400-600 times, or 60% pyraclostrobin metiram (Cabrio Top) at 1200 times, or 70% metiram (Polyram) at 700 times for root drenching or spraying.
4. Chemical control: Spray 72% cymoxanil mancozeb (Curzate) wettable powder at 700 times, or 50% dimethomorph (Acrobat) wettable powder at 2500 times, or 25% mandipropamid (Revus) at 2500 times, 70% fosetyl-aluminum · mancozeb wettable powder at 500 times, 72.2% propamocarb hydrochloride (Previcur, Zaisheng) aqueous solution at 800 times, 58% metalaxyl % mancozeb (Jinlei) wettable powder at 500 times, 64% oxadixyl · mancozeb (Sandofan) wettable powder at 500 times, once every 7-10 days, for 3-4 consecutive applications. If necessary, the above fungicides can also be used for root drenching, pouring 0.25-0.4 liters of the prepared solution per plant. If spraying and root drenching can be carried out simultaneously, the control effect is significantly improved.