Meyer M D, Hausbeck M K
Department of Plant Pathology, Michigan State University, East Lansing 48824.
Plant Dis. 2013 Jan;97(1):107-112. doi: 10.1094/PDIS-12-11-1071-RE.
Phytophthora crown and root rot (Phytophthora capsici) of summer squash is especially difficult to manage because all commercial cultivars are highly susceptible to P. capsici. Producers have traditionally relied on foliar fungicide applications to control Phytophthora crown and root rot despite their limited efficacy. Soil fungicide applications, including via subsurface drip chemigation, have recently gained interest as a method of improving control of P. capsici infections. In this study, soil drenches and foliar applications of 11 fungicides were compared for control of Phytophthora crown and root rot of summer squash in replicated field and greenhouse trials. Fungicides were applied at 7-day intervals. Incidence (%) of plant death was assessed from 7 to 42 days post inoculation (dpi) in field trials. Crown rot severity was rated on a scale of 1 (no wilting) to 5 (plant death) from 5 to 21 dpi in greenhouse trials. Results of field and greenhouse trials were similar. Plant death of 'Cougar' following inoculation with P. capsici isolate 12889 occurred at all growth stages from first true-leaf to full maturity in field trials. Plant death 42 dpi differed significantly (P ≤ 0.0001) among fungicides and application methods. The fungicide-application method interaction also was significant. Some fungicides were ineffective regardless of application method. In general, soil drenches were more effective than foliar applications at limiting plant death but no treatment completely controlled disease symptoms. Mean plant death 42 dpi was 41% for soil drenches and 92% for foliar sprays. Drenches of fluopicolide, mandipropamid, or dimethomorph limited plant death to ≤10% and prevented yield loss associated with root and crown rot. Foliar applications generally did not reduce plant death compared with the untreated, inoculated control, and were unable to prevent yield loss in field trials. In greenhouse trials, crown rot severity differed significantly (P ≤ 0.0001) among fungicides, application methods, and cultivars when plants were inoculated with P. capsici isolate 12889 or SP98. Crown rot was less severe and disease progress was slower following soil drenches than foliar applications. Some fungicide treatments were more effective on 'Leopard,' which was less susceptible to P. capsici than 'Cougar.' Soil application methods, including soil drench and drip chemigation, should be evaluated when fungicides are registered for soilborne disease control, because these methods provide better control of Phytophthora crown and root rot than foliar application.
西葫芦的辣椒疫霉冠腐病和根腐病（由辣椒疫霉引起）特别难以防治，因为所有商业栽培品种对辣椒疫霉都高度敏感。尽管叶面施用杀菌剂的效果有限，但生产者传统上一直依赖于叶面施用杀菌剂来防治辣椒疫霉冠腐病和根腐病。包括通过地下滴灌化学灌溉施用土壤杀菌剂，最近作为一种改善辣椒疫霉感染防治效果的方法受到了关注。在本研究中，在重复的田间和温室试验中，比较了11种杀菌剂的土壤浇灌和叶面施用对西葫芦辣椒疫霉冠腐病和根腐病的防治效果。杀菌剂每隔7天施用一次。在田间试验中，接种后7至42天评估植株死亡发生率（%）。在温室试验中，从接种后5至21天，根据冠腐病严重程度从1（无萎蔫）到5（植株死亡）进行评分。田间和温室试验结果相似。在田间试验中，用辣椒疫霉分离株12889接种后，‘美洲狮’品种从第一片真叶到完全成熟的所有生长阶段都出现了植株死亡。接种后42天，不同杀菌剂和施用方法之间的植株死亡率差异显著（P≤0.0001）。杀菌剂施用方法的交互作用也很显著。有些杀菌剂无论采用何种施用方法都无效。一般来说，在限制植株死亡方面，土壤浇灌比叶面施用更有效，但没有一种处理能完全控制病害症状。土壤浇灌处理接种后42天的平均植株死亡率为41%，叶面喷雾处理为92%。氟吡菌酰胺、双炔酰菌胺或烯酰吗啉浇灌可将植株死亡率限制在≤10%，并防止与根腐病和冠腐病相关的产量损失。与未处理的接种对照相比，叶面施用通常不能降低植株死亡率，并且在田间试验中无法防止产量损失。在温室试验中，当用辣椒疫霉分离株12889或SP98接种植株时，不同杀菌剂、施用方法和品种之间的冠腐病严重程度差异显著（P≤0.0001）。与叶面施用相比，土壤浇灌后冠腐病严重程度较低，病害进展较慢。一些杀菌剂处理对‘豹纹’品种更有效，该品种对辣椒疫霉的敏感性低于‘美洲狮’。当杀菌剂登记用于防治土传病害时，应评估包括土壤浇灌和滴灌化学灌溉在内的土壤施用方法，因为这些方法比叶面施用能更好地防治辣椒疫霉冠腐病和根腐病。
