Die-back of Phragmites australis in the Mississippi River Delta (MRD), Louisiana, USA, is associated with large populations of nonnative Roseau Cane Scale (RCS), Nipponaclerda biwakoensis. Initial observations suggested different P. australis phenotypes displayed different susceptibilities to scale infestation and die-back, but the role of scale infestation on die-back was unknown. To understand the effect of RCS on P. australis, paired stands of Delta and European phenotypes in the MRD were monitored for stem heights, densities, and scale infestation over two years. A mesocosm experiment was conducted to assess whether RCS abundance and P. australis growth were dependent on water salinity and phenotype. Three Phragmites australis phenotypes were grown in small pools under fresh or mesohaline conditions, and RCS infestated or non-infested treatments. Scale densities were up to 7 times greater on the Delta compared to the European phenotype. Scale infestation resulted in 22%–39% reductions in the proportion of stems with green leaf tissue for all phenotypes, and 12% reduction in stem heights for Delta-type. Salinity was detrimental to all phenotypes, reducing stem heights by 20% compared to freshwater. Our results provide evidence that the RCS can result in die-back symptoms similar to what is observed in the MRD.

美国路易斯安那州密西西比河三角洲（MRD）的芦苇死死与Nipponaclerda biwakoensis的大量非本地Roseau Cane Scale（RCS）有关。最初的观察结果表明，不同的澳大利亚败血症表型对鳞屑侵染和死亡具有不同的敏感性，但是鳞屑侵染对死亡的作用尚不清楚。为了了解RCS对澳大利亚假单胞菌的影响，在两年中监测了MRD中成对的Delta和欧洲表型配对的茎高，密度和鳞屑侵扰。进行了介观试验，以评估RCS丰度和南方假单胞菌生长取决于水的盐度和表型。在新鲜或中盐条件下，在小型池中培养了三种芦苇表型，RCS感染或未感染。与欧洲的表型相比，三角洲的尺度密度高出7倍。规模侵染导致所有表型的带有绿叶组织的茎的比例减少了22％–39％，而对于Delta型的则使茎高降低了12％。盐分对所有表型都是有害的，与淡水相比，茎高降低了20％。我们的结果提供了证据，表明RCS可以导致与MRD中观察到的相似的消退症状。