Soybean seedlings are vulnerable to different oomycete pathogens. Seed treatments containing the two antioomycete (oomicide) chemicals, metalaxyl-M (mefenoxam) and ethaboxam, are used for protection against oomycete pathogens. This study aimed to evaluate the influence of these two oomicides on isolation probability of oomycetes from soybean taproot or lateral root sections. Soybean plants were collected between the first and third trifoliate growth stages from five Midwest field locations in 2016 and four of the same fields in 2017. Oomycetes were isolated from taproot and lateral root. In 2016, 369 isolation attempts were completed, resulting in 121 isolates from the taproot and 154 isolates from the lateral root. In 2017, 468 isolation attempts were completed, with 44 isolates from the taproot and 120 isolates from the lateral roots. In three of nine site-years, the probability of isolating an oomycete from a taproot or lateral root section was significantly different. Seed treatments containing a mixture of ethaboxam and metalaxyl significantly reduced the probability of oomycete isolation from lateral roots in Illinois in 2016 and 2017, but not in other locations, which may have been related to the heavy soil type (clay loam). Among the 439 isolates collected from the two years sampled, 24 oomycete species were identified, and community compositions differed depending on location and year. The five most abundant species were Pythium sylvaticum (28.9%), P. heterothallicum (14.3%), P. ultimum var. ultimum (11.8%), P. attrantheridium (7.9%), and P. irregulare (6.6%), which accounted for 61.7% of the isolates collected. Oomicide sensitivity to ethaboxam and mefenoxam was assessed for >300 isolates. There were large differences in ethaboxam sensitivity among oomycete species, with effective concentrations to reduce optical density at 600 nm by 50% compared with the nonamended control (EC₅₀ values) ranging from <0.01 to >100 μg/ml and a median of 0.65 μg/ml. Isolates with insensitivity to ethaboxam (>12 μg/ml) belonged to the species P. torulosum and P. rostratifingens but were sensitive to mefenoxam. Oomicide sensitivity to mefenoxam ranged from <0.01 to 0.62 μg/ml with a median of 0.03 μg/ml. The mean EC₅₀ value of the five most abundant species to ethaboxam ranged from 0.35 to 0.97 μg/ml of ethaboxam and from 0.02 to 0.04 μg/ml of mefenoxam. No shift in sensitivity to mefenoxam or ethaboxam was observed as a result of soybean seed treatment or year relative to the nontreated seed controls. In summary, this study contributed to the understanding of the composition of oomycete populations from different soybean root tissues, locations, years, and seed treatments. Finally, seed treatments containing mefenoxam or metalaxyl plus ethaboxam can be effective in reducing the probability of oomycete isolation from soybean roots.

大豆幼苗容易受到不同卵菌病原体的影响。含有两种抗卵菌（杀卵剂）化学物质甲霜灵（精甲霜灵）和噻唑菌胺的种子处理剂用于防止卵菌病原体。本研究旨在评估这两种杀卵剂对大豆主根或侧根切片中卵菌分离概率的影响。 2016 年从中西部的 5 个田地和 2017 年的 4 个相同田地收集了第一和第三三叶生长期之间的大豆植物。从主根和侧根中分离出卵菌。 2016年，完成了369次分离尝试，从主根分离出121个分离物，从侧根分离出154个分离物。 2017年，共完成468次分离尝试，其中主根分离44个，侧根分离120个。在九个站点年中的三个中，从主根或侧根部分分离卵菌的概率显着不同。 2016年和2017年，含有噻唑菌胺和甲霜灵混合物的种子处理显着降低了伊利诺伊州从侧根分离卵菌的可能性，但在其他地方则没有，这可能与重质土壤类型（粘壤土）有关。在两年采样中收集的 439 个分离株中，鉴定出 24 个卵菌物种，群落组成因地点和年份而异。含量最多的五个物种是Pythium syvaticum (28.9%)、 P. hetothallicum (14.3%)、 P. ultimum var. ultimum (11.8%)、 P. attrantheridium (7.9%) 和P.规则不规则(6.6%)，占收集的分离株的 61.7%。 评估了超过 300 个分离株对噻唑菌胺和精甲霜灵的杀螨剂敏感性。卵菌物种之间的噻唑菌胺敏感性存在很大差异，与未修正的对照（EC ₅₀值）相比，有效浓度可将 600 nm 处的光密度降低 50%，范围为 <0 id=23>100 μg/ml，中位数为0.65微克/毫升。对噻唑菌胺 (>12 μg/ml) 不敏感的分离株属于P. torulosum和P. rostratifingens ，但对精甲霜灵敏感。对精甲唑菌胺的杀螨剂敏感性范围为 <0 id=26>50 五个最丰富的物种对噻唑菌胺的值范围为 0.35 至 0.97 μg/ml 噻唑菌胺和 0.02 至 0.04 μg/ml 精甲唑菌胺。相对于未处理的种子对照，未观察到对精甲霜灵或噻唑菌胺的敏感性因大豆种子处理或年份的变化而变化。总之，这项研究有助于了解不同大豆根组织、地点、年份和种子处理的卵菌种群的组成。最后，含有精甲霜灵或甲霜灵加噻唑菌胺的种子处理可有效降低从大豆根部分离卵菌的可能性。