Gent David H, Nelson Mark E, Grove Gary G, Mahaffee Walter F, Turechek William W, Woods Joanna L
United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Forage Seed and Cereal Research Unit, and Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331.
Department of Plant Pathology, Washington State University Irrigated Agriculture Research and Extension Center, Prosser 99350.
Plant Dis. 2012 Sep;96(9):1343-1351. doi: 10.1094/PDIS-01-12-0084-RE.
Downy mildew (caused by Pseudoperonospora humuli) and powdery mildew (caused by Podosphaera macularis) are important diseases of hop in the Pacific Northwest United States, and cultural practices may affect the severity of both diseases. The association of spring pruning quality and timing with severity of downy mildew and powdery mildew was assessed through analysis of survey data collected from commercial hop yards in Oregon and Washington. Among 149 hop yards surveyed, the most common pruning method was chemical desiccation (48% of yards), mechanical pruning (23%), or a combination of these practices (15%). The quality of pruning was assessed using a three-category ordinal scale ("excellent", "moderate", or "poor") based on the amount of foliage remaining on plants following pruning. Excellent pruning quality was attained more often in yards pruned twice (74.6 to 82.1% of yards) versus once (33.8% of yards), independent of pruning method. Seasonal severity of downy mildew in Oregon increased approximately twofold with reduction in pruning quality from excellent to moderate to poor. Pruning quality was not significantly related to levels of powdery mildew on leaves or cones in Oregon. Under more severe disease pressure in Washington, however, seasonal severity of powdery mildew on leaves and the incidence of cones with powdery mildew were significantly greater in yards that had poor pruning compared with excellent pruning. Moreover, yards that had excellent pruning quality received, on average, 1.1 to 1.5 fewer fungicide applications per season for downy mildew or powdery mildew compared with yards that had moderate or poor pruning quality. This savings was associated with delayed initiation of the first application by 7.5 to 14.2 days in yards with excellent pruning quality. Replicated experiments in commercial yards in Oregon quantified the effect of delaying pruning timing 5 to 21 days compared with growers' standard practices on the diseases and yield. Downy mildew suppression by delayed pruning was dependent on cultivar and year of sampling, being significantly reduced fivefold only in 'Willamette' in 2007. Severity of powdery mildew and cone yield was similar between plots that received the delayed or standard pruning timing treatments. Collectively, these studies emphasize that early spring sanitation measures are associated with reduced primary inoculum and are critically important for managing both downy mildew and powdery mildew. A savings of at least one fungicide application per year appears achievable when spring pruning is conducted thoroughly and slightly delayed compared with growers' current practices.
霜霉病（由葎草假霜霉菌引起）和白粉病（由黄斑叉丝单囊壳菌引起）是美国太平洋西北地区啤酒花的重要病害，栽培措施可能会影响这两种病害的严重程度。通过对从俄勒冈州和华盛顿州的商业啤酒花种植园收集的调查数据进行分析，评估了春季修剪质量和时间与霜霉病和白粉病严重程度之间的关联。在调查的149个啤酒花种植园中，最常见的修剪方法是化学干燥（占种植园的48%）、机械修剪（23%）或这些方法的组合（15%）。根据修剪后植株上残留的叶片数量，使用三级有序量表（“优秀”、“中等”或“差”）对修剪质量进行评估。与只修剪一次的种植园（33.8%）相比，在修剪两次的种植园中（74.6%至82.1%）更常达到优秀的修剪质量，这与修剪方法无关。在俄勒冈州，随着修剪质量从优秀降至中等再降至差，霜霉病的季节性严重程度增加了约两倍。在俄勒冈州，修剪质量与叶片或球果上的白粉病水平没有显著关系。然而，在华盛顿州病害压力更大的情况下，与修剪优秀的种植园相比，修剪差的种植园叶片上白粉病的季节性严重程度以及球果感染白粉病的发生率显著更高。此外，与修剪质量中等或差的种植园相比，修剪质量优秀的种植园每个季节用于防治霜霉病或白粉病的杀菌剂平均少施用1.1至1.5次。这种节省与修剪质量优秀的种植园首次施用杀菌剂的时间推迟7.5至14.2天有关。在俄勒冈州商业种植园进行的重复实验量化了与种植者的标准做法相比，将修剪时间推迟5至21天对病害和产量的影响。推迟修剪对霜霉病的抑制作用取决于品种和采样年份，仅在2007年的“威拉米特”品种中显著降低了五倍。接受推迟或标准修剪时间处理的地块之间，白粉病严重程度和球果产量相似。总体而言，这些研究强调早春卫生措施与减少初始接种体有关，对于管理霜霉病和白粉病至关重要。与种植者目前的做法相比，如果春季修剪进行得彻底且稍有延迟，每年至少可节省一次杀菌剂施用。
