Tar spot on corn, caused by the fungus (Phyllachora maydis Maubl. [Phyllachorales: Phyllachoraceae]), is an emerging disease in the United States. In 2018 and 2019, significant but localized epidemics of tar spot occurred across the major corn producing region of the Midwest. After being first detected in 2015, tar spot was detected in 135 and 139 counties where the disease was not previously detected in 2018 and 2019, respectively, and is now established across 310 counties across the United Sates. Foliage with signs (stromata) of P. maydis and symptoms of tar spot were collected from 128 fields in 2018 and 191 fields in 2019, across seven states. Samples were assessed for severity of fungal stromata (percent leaf area covered with stromata) on foliage and the incidence of fisheye lesions (proportion of lesions with fisheye symptoms) associated with fungal stromata. Stromatal severity on samples in 2018 ranged from 0.5 to 67% and incidence of fisheye lesions ranged from 0 to 12%, whereas in 2019, stromatal severity ranged from 0.1 to 35% and incidence of fisheye lesions ranged from 0 to 80%, with 95% of samples presenting less than 6% incidence of fisheye lesions. Tar spot has spread substantially from where it was first reported in the United States. Collaborative efforts to monitor the spread and educate clientele on management are essential as this disease spreads into new areas.

中文翻译：

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在美国记录玉米疫霉菌的建立，传播和严重程度

在美国，由真菌引起的玉米焦油斑（Phyllachora maydis Maubl。[Phyllachorales：Phyllachoraceae]）是一种新兴疾病。在2018年和2019年，中西部主要玉米产区出现了焦油斑的重要但局部的流行病。在2015年首次检测到焦油斑点之后，分别在135个和139个县中检测到了焦油斑点，而以前在2018年和2019年均未发现该病，现在在美国的310个县中建立了焦油斑点。叶子随着迹象（子座）P.玉米小斑病分布在七个州的2018年和2019年的191个油田收集了焦油斑点的症状和症状。评估了样品在树叶上的真菌基质的严重程度（叶覆盖的叶面积百分比）以及与真菌基质相关的鱼眼病变的发生率（具有鱼眼症状的病变比例）。2018年样本的气孔严重度为0.5％至67％，鱼眼病变的发生率为0至12％，而2019年，气孔严重度为0.1％至35％，鱼眼病变的发生率为0至80％，其中95％表示鱼眼病变发生率低于6％的样本的百分比。焦油斑点已从美国首次报道的地方大量扩散。随着这种疾病蔓延到新的领域，监测疾病传播和对客户进行管理的合作努力至关重要。