蔓枯病对西瓜危害极重,能造成西瓜大面积减产,甚至绝收,必须引起瓜农的警惕。蔓枯病又叫黑腐病,是一种真菌性病害,由子囊菌侵染所致。病菌在病残植株上或混入土中越冬,翌年借风雨传播。高温多雨、天气闷热时,病势发展迅速;重茬地、低洼地或雨后积水、缺肥以及生长衰弱的地块,发病均重;过度密植,光照不好、通风不良时,也易发病。蔓枯病症状:叶、茎、果实均能受侵害,但以叶片受害最重。叶片受害后,出现直径1～2厘米灰黑色圆形或不规则圆形同心轮纹病斑,发生在叶缘上一般为弧状形。老病叶的病斑上有黑色小点,病叶干枯时常呈星状破裂(俗称菱角形黑斑),气候潮湿时严重蔓延,全叶变黑桔死,蔓上主要在节 Vulgaris are extremely devastating to watermelon and can cause large-scale production of watermelon or even excessive harvest, and vigilance of melon farmers must be taken. Bacterial blight, also known as black rot, is a fungal disease caused by Ascomycosis infection. Bacteria in the sick plant or winter mixed with soil, the following year spread by wind and rain. Hot and rainy, the weather is hot, the rapid development of disease; cropping, low ground or rain water, lack of fat and growth of weak land, the incidence is heavy; over-dense, poor lighting, poor ventilation, but also prone to disease. Symptoms of vomiting: leaves, stems, fruits can be infested, but to suffer the most leaf damage. Leaf damage, the emergence of 1 to 2 cm in diameter gray-black circular or irregular circular concentric pattern of round spots, occurs in the leaf margin is generally arc-shaped. Old sick leaves spots on the black dots, the diseased leaves often dry star-shaped rupture (commonly known as water chestnut spots), the weather was severe spread of dampness, the whole leaf turns black orange die, spread on the main section