典型的症状,叶片正面和边缘有淡黄色或黄绿色的病斑,病斑呈圆形或近于圆形,扩展很快,没有明显边缘,病斑反面有厚的蓝灰色或灰褐色的霜霉层;苗床上的病苗也表现蓝灰色,这是由于病斑上水层反映的缘故,因此国外也称为蓝霉病(一般干的叶片上表现灰褐色)。病斑发展下去,逐步变为褐色,以至深褐色,最后成为枯褐色;在干叶子上病斑表面有凸起,老病斑边缘有一层青褐色与马铃薯晚疫病症状相似。烘烤过的烟叶,隐约可以看出,湿度大时病斑更为明显。这种病斑有时很容易与烟草黑胫病混淆,黑胫病病斑,也呈现蓝褐色但病斑较大,带有水渍状,背面霉层很稀少,毛短、白色,病斑为圆斑形;而烟草霜霉病斑则呈多角形。 Typical symptoms are yellow or yellow-green lesions on the front and edges of the leaves, round or near-rounded lesions, rapid expansion, no visible edges, thick blueish-gray or beige cream on the opposite side of the lesion Mold layer; seedling seedlings also appear blue-gray color, which is due to the reflection of water spots on the lesion, so abroad is also known as blue mildew (usually dry leaves on the performance of brown). Lesions continue to develop, and gradually become brown, even dark brown, and finally become brown; on the surface of the leaves on the leaves have raised, the old lesion edge layer of brown and potato late blight symptoms similar. Baked tobacco, can be seen vaguely, when the humidity is more obvious lesions. This lesion is sometimes confused with tobacco black shank disease. Black shank lesions also show a bluish-brown but larger spots with water stains. The back mold layer is sparse, short, white, Circular spot; tobacco downy mildew spot was polygonal.