Gent D H, James D G, Wright L C, Brooks D J, Barbour J D, Dreves A J, Fisher G C, Walton V M
Forage and Cereal Research Unit, USDA-ARS, and Department of Botany and Plant Pathology, Oregon State University, 3450 SW Campus Way, Corvallis OR 97331, USA.
J Econ Entomol. 2009 Feb;102(1):274-86. doi: 10.1603/029.102.0137.
Twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and hop aphid, Phorodon humuli (Schrank) (Hemiptera: Aphididae), are the most important arthropod pests of hop (Humulus lupulus L.) in the Northern Hemisphere. A potential barrier for greater adoption of conservation biological control strategies for spider mites and hop aphid is the extensive use of fungicides for management of hop powdery mildew, Podosphaera macularis (Wallr.:Fr.) U. Braun & S. Takamatsu. Field studies conducted in experimental plots in Oregon and Washington in 2005 and 2006 quantified the effects of powdery mildew fungicide programs (i.e., sulfur, paraffinic oil, and synthetic fungicides) on arthropod pests and natural enemies on hop. Fungicide treatment significantly affected spider mite populations in all four studies. Multiple applications of sulfur fungicides applied before burr development resulted in 1.4-3.3-fold greater spider mite populations during summer. Near the cessation of the sulfur applications, or after a lag of 20-30 d, spider mite populations increased significantly faster on sulfur treated plants compared with water-treated plants in three of four experiments. The effect of paraffinic oil on spider mites was varied, leading to exacerbation of spider mites in Oregon and Washington in 2005, suppression of mites in Oregon in 2006, and no significant effect compared with water in Washington in 2006. Significant relative treatment effects for cone damage due to spider mite feeding were detected in Oregon in 2005 in plots treated with sulfur and paraffinic oil compared with water and synthetic fungicides. Mean populations of hop aphids were similar among treatments in Oregon, although sulfur treatment suppressed hop aphid populations in Washington in 2005 and 2006. Populations of individual predacious insect species and cumulative abundance of macropredators were not consistently suppressed or stimulated by treatments in all trials. However, predatory mite abundance in Washington was affected by fungicide treatments, with plots treated with sulfur consistently having 10-fold fewer phytoseiids per leaf compared with the other treatments. Based on the results of these studies, powdery mildew fungicide programs that minimize or eliminate applications of sulfur and paraffinic oil would tend to conserve predatory mites and minimize the severity of spider mite outbreaks. However, mechanisms other than direct or indirect toxicity to phytoseiid mites likely are associated with exacerbation of spider mite outbreaks on hop.
二斑叶螨，朱砂叶螨科赫（蜱螨亚纲：叶螨科），以及啤酒花蚜，啤酒花瘤蚜（施兰克）（半翅目：蚜科），是北半球啤酒花（忽布属啤酒花）最重要的节肢动物害虫。叶螨和啤酒花蚜保护生物防治策略未能更广泛采用的一个潜在障碍是，大量使用杀菌剂来防治啤酒花白粉病，即黄斑叉丝单囊壳（瓦尔：弗）U. 布劳恩和高松。2005年和2006年在俄勒冈州和华盛顿州的试验田进行的田间研究，量化了白粉病杀菌剂方案（即硫磺、石蜡油和合成杀菌剂）对啤酒花上节肢动物害虫和天敌的影响。在所有四项研究中，杀菌剂处理对叶螨种群有显著影响。在毛刺发育前多次施用硫磺杀菌剂，导致夏季叶螨种群数量增加1.4至3.3倍。在硫磺施用接近停止时，或在延迟20至30天后，在四项试验中的三项试验中，与水处理植物相比，硫磺处理植物上的叶螨种群数量增加明显更快。石蜡油对叶螨的影响各不相同，导致2005年俄勒冈州和华盛顿州的叶螨数量增加，2006年俄勒冈州的叶螨数量受到抑制，2006年在华盛顿州与水处理相比无显著影响。2005年在俄勒冈州，与水处理和合成杀菌剂处理相比，在硫磺和石蜡油处理的地块中，检测到因叶螨取食导致的球果损伤有显著的相对处理效应。在俄勒冈州，各处理间啤酒花蚜的平均种群数量相似，尽管硫磺处理在2005年和2006年抑制了华盛顿州的啤酒花蚜种群数量。在所有试验中，各捕食性昆虫种类的种群数量和大型捕食者的累积丰度并未因处理而持续受到抑制或刺激。然而，华盛顿州的捕食螨丰度受到杀菌剂处理的影响，与其他处理相比，硫磺处理的地块每片叶上的植绥螨数量始终少10倍。基于这些研究结果，尽量减少或消除硫磺和石蜡油施用的白粉病杀菌剂方案，往往有助于保护捕食螨，并最大限度地减少叶螨爆发的严重程度。然而，除了对植绥螨的直接或间接毒性外，其他机制可能与啤酒花叶螨爆发的加剧有关。
