分布及为害榆韧皮部坏死病 Elm phloem necro-sis 只在美国发生为害。该病在1938年 swin-gle 首先报道,接着他又发表了病害在俄亥俄河流域发生流行,使很多美洲榆致死的调查研究。在1967年以前,大多数黄化型病害都认为是病毒所致,故他断定榆韧皮部坏死病也是由病毒引起。早期的报道(Garman,1899;Forbes,1912)有证据表明:该病在很久以前,可能早在1882年,就在俄亥俄河 Distribution and damage elm phloem necrosis Elm phloem necro-sis harm only in the United States. The disease was first reported by the swin-gle in 1938, and then he published another study investigating the prevalence of disease in the Ohio River basin, which has led to the death of many American wilts. Before 1967, most yellow-type diseases were thought to be caused by the virus, so he concluded that elm phloem necrosis was also caused by a virus. Earlier reports (Garman, 1899; Forbes, 1912) have shown that the disease was long ago, possibly as early as 1882, on the Ohio River