Center for Integrated Fungal Research, Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC 27695.
Department of Plant and Environmental Sciences, Clemson University, Coastal Research and Education Center, Charleston, SC 29414.
Plant Dis. 2022 Mar;106(3):1009-1019. doi: 10.1094/PDIS-09-21-1992-RE. Epub 2022 Mar 8.
Cucurbit downy mildew caused by the oomycete is an important disease that affects members of Cucurbitaceae family globally. However, temporal dynamics of the disease have not been characterized at the field scale to understand how control strategies influence disease epidemics. Disease severity was assessed visually on cucumber and summer squash treated with weekly alternation of chlorothalonil with cymoxanil, fluopicolide, or propamocarb during the 2018 spring season and 2019 and 2020 fall seasons in North Carolina and the 2018 and 2020 fall seasons in South Carolina. Disease onset was observed around mid-June during the spring season and early September during the fall season, followed by a rapid increase in severity until mid-July in the spring season and late September or mid-October in the fall season, typical of polycyclic epidemics. The Gompertz, logistic, and monomolecular growth models were fitted to disease severity using linear regression and parameter estimates to compare the effects of fungicide treatment and cucurbit host type on disease progress. The Gompertz and logistic models were more appropriate than the monomolecular model in describing temporal dynamics of cucurbit downy mildew, with the Gompertz model providing the best description for 34 of the 44 epidemics examined. Fungicide treatment and host type significantly ( < 0.0001) affected the standardized area under disease progress curve (sAUDPC), final disease severity (Final DS), and weighted mean absolute rates of disease progress (ρ), with these variables, in most cases, being significantly ( < 0.05) lower in fungicide-treated plots than in untreated control plots. Except in a few cases, sAUDPC, Final DS, and ρ were lower in cases where chlorothalonil was alternated with fluopicolide or propamocarb than in cases where chlorothalonil was alternated with cymoxanil or when chlorothalonil was applied alone. These results characterized the temporal progress of cucurbit downy mildew and provided an improved understanding of the dynamics of the disease at the field level. Parameters of disease progress obtained from this study could serve as inputs in simulation studies to assess the efficacy of fungicide alternation in managing fungicide resistance in this pathosystem.
由卵菌引起的葫芦科霜霉病是一种重要的疾病，它会影响全球葫芦科植物。然而，在田间尺度上，尚未对疾病的时间动态进行描述，以了解控制策略如何影响疾病流行。在北卡罗来纳州，2018 年春季、2019 年和 2020 年秋季以及南卡罗来纳州，2018 年秋季和 2020 年秋季，每周交替使用氯噻啉、咯菌腈、氟吡菌酰胺或丙森锌处理黄瓜和夏南瓜，评估了疾病严重程度。春季在 6 月中旬左右观察到发病，秋季在 9 月初，然后病情迅速加重，春季在 7 月中旬，秋季在 9 月底或 10 月中旬达到高峰，这是多循环流行的典型特征。使用线性回归和参数估计，将疾病严重程度与杀菌剂处理和葫芦宿主类型进行拟合，以比较杀菌剂处理和葫芦宿主类型对病害进展的影响。结果表明，与单分子模型相比，Gompertz 和 logistic 模型更适合描述葫芦科霜霉病的时间动态，在 44 个研究的流行期中，有 34 个流行期 Gompertz 模型的描述效果最好。杀菌剂处理和宿主类型显著（<0.0001）影响病害进展标准化累积受害面积（sAUDPC）、最终病害严重度（Final DS）和病害进展加权平均绝对速率（ρ），在大多数情况下，处理区的这些变量明显（<0.05）低于未处理对照区。除了少数情况外，交替使用氯噻啉和氟吡菌酰胺或丙森锌比交替使用氯噻啉和咯菌腈或单独使用氯噻啉时，sAUDPC、Final DS 和 ρ 较低。这些结果描述了葫芦科霜霉病的时间进程，并提供了对田间水平疾病动态的更好理解。本研究获得的病害进展参数可作为模拟研究的输入，以评估杀菌剂交替在管理该病原系统中杀菌剂抗性方面的功效。
