一、症状榆荷兰病的症状随榆种、病原菌株、发病期的早晚、当年天气、侵染方式及寄主生长势等而不同,主要有下述两种类型: 1.树冠上层个别枝条叶片变黄并逐渐脱落,进而向周围更多的枝叶扩展,远看树冠有一明显的由稀疏的黄叶和秃枝构成的“病灶”,细看病枝条分叉处常有小蠹虫的蛀食槽。 First, the symptoms Yu Dutch disease symptoms with elm species, pathogen strains, the onset of the morning and evening, the weather, the way of infection and the host growth potential and so different, there are two main types: 1. Canopy above the individual branches of the leaves change Yellow and gradually fall off, and then to the surrounding more branches and leaves to expand, as seen from the crown there is a clear sparse yellow leaves and bald constitute the “lesion”, look at the branch of the bifurcation often beater baterial groove.