Bounds R S, Podolsky R H, Hausbeck M K
Former Graduate Assistant, Department of Plant Pathology, Michigan State University, East Lansing 48824-1311.
Assistant Professor, Center for Biotechnology and Genomic Medicine, Medical College of Georgia, Augusta 30912-2400.
Plant Dis. 2007 Jul;91(7):798-804. doi: 10.1094/PDIS-91-7-0798.
Cercospora carotae and Alternaria dauci cause foliar blight on carrot (Daucus carota subsp. sativus) and are managed with fungicides to prevent yield loss. Sprays are initiated prior to disease symptoms and reapplied frequently, but some of these applications may not be necessary when the threat of disease is low. Delaying the initial fungicide spray until disease symptoms are observed and applying subsequent sprays according to the TOM-CAST disease forecaster may reduce fungicide inputs. The objective of this 2-year field study was to compare preventive, calendar-based application schedules with an integrated management approach that incorporates disease scouting to initiate fungicide application and the TOM-CAST system for timing subsequent fungicide sprays to manage foliar blight on processing, fresh market, and cut-and-peel carrot cultivars in Michigan. Applications of the fungicides chlorothalonil alternated with azoxystrobin were made prior to disease symptoms (0% blight) or when the foliage became blighted at a trace, 5%, or 10% severity level. Fungicides were reapplied every 7 or 10 days or according to TOM-CAST using disease severity value (DSV) thresholds of 15, 20, or 25. Initiating fungicide treatment at a trace level of disease and timing subsequent sprays according to the TOM-CAST 15-DSV forecaster was comparable to the preventive, calendar-based fungicide regime. One to five fewer applications were needed, while fungicide costs were reduced by $21 to $141 per hectare, when spraying at the trace disease threshold and reapplying according to the TOM-CAST 15-DSV program compared with the 7- or 10-day intervals initiated at 0% blight. Fungicide programs initiated at 5 or 10% leaf blight often provided less control than programs initiated at 0% and trace disease. This study highlights the importance of initiating a fungicide program prior to advanced foliar blight and validates the TOM-CAST 15-DSV forecaster for managing Cercospora leaf spot and Alternaria leaf blight in three carrot production systems.
胡萝卜尾孢菌和胡萝卜链格孢菌会引发胡萝卜（胡萝卜亚种）叶斑病，可通过使用杀菌剂来防治以避免产量损失。在病害症状出现之前就开始喷洒杀菌剂，并频繁重新喷洒，但当病害威胁较低时，其中一些喷洒可能并无必要。将首次杀菌剂喷洒推迟至观察到病害症状，并根据TOM - CAST病害预测仪进行后续喷洒，可能会减少杀菌剂的使用量。这项为期两年的田间研究的目的是，将基于日历的预防性施药方案与综合管理方法进行比较，该综合管理方法包括通过病害巡查来启动杀菌剂施用，以及使用TOM - CAST系统来确定后续杀菌剂喷洒的时间，以防治密歇根州加工型、鲜食型和去皮型胡萝卜品种的叶斑病。在病害症状出现之前（0%叶斑病）或当叶片出现微量、5%或10%严重程度的叶斑病时，交替施用百菌清和嘧菌酯这两种杀菌剂。杀菌剂每7天或10天重新喷洒一次，或者根据TOM - CAST使用15、20或25的病害严重度值（DSV）阈值进行喷洒。在病害微量水平时开始杀菌剂处理，并根据TOM - CAST 15 - DSV预测仪确定后续喷洒时间，这与基于日历的预防性杀菌剂方案相当。与在0%叶斑病时开始的7天或10天间隔喷洒相比，在微量病害阈值时喷洒并根据TOM - CAST 15 - DSV程序重新喷洒，所需喷洒次数可减少1至5次，同时每公顷杀菌剂成本可降低21美元至141美元。在5%或10%叶斑病时开始的杀菌剂方案，其防治效果通常不如在0%和微量病害时开始的方案。这项研究突出了在叶斑病严重之前启动杀菌剂方案的重要性，并验证了TOM - CAST 15 - DSV预测仪在三种胡萝卜生产系统中管理尾孢菌叶斑病和链格孢菌叶斑病的有效性。
