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Spatiotemporal Description of Epidemics Caused by Phoma ligulicola in Tasmanian Pyrethrum Fields

Citation

Pethybridge, SJ and Esker, P and Hay, FS and Wilson, CR and Nutter, FW, Jr, Spatiotemporal Description of Epidemics Caused by Phoma ligulicola in Tasmanian Pyrethrum Fields, Phytopathology, 95, (6) pp. 648-658. ISSN 0031-949X (2005) [Refereed Article]

DOI: doi:10.1094/PHYTO-95-0648

Abstract

Spatial and temporal patterns of foliar disease caused by Phoma ligulicola were quantified in naturally occurring epidemics in Tasmanian pyrethrum fields. Disease assessments (defoliation incidence, defoliation severity, incidence of stems with ray blight, and incidence of flowers with ray blight) were performed four times each year in 2002 and 2003. Spatial analyses based on distribution fitting, runs analysis, and spatial analysis by distance indices (SADIE) demonstrated aggregation in fields approaching their first harvest for all assessment times between September and December. In second-year harvest fields, however, the incidence of stems with ray blight was random for the first and last samplings, but aggregated between these times. Spatiotemporal analyses were conducted between the same disease intensity measures at subsequent assessment times with the association function of SADIE. In first-year harvest fields, the presence of steep spatial gradients was suggested, most likely from dispersal of conidia from foci within the field. The importance of exogenous inoculum sources, such as wind-dispersed ascospores, was suggested by the absence of significant association between defoliation intensity (incidence and severity) and incidence of stems with ray blight in second-year harvest fields. The logistic model provided the best temporal fit to the increase in defoliation severity in each of six first-year harvest fields in 2003. The logistic model also provided the best fit for the incidence of stems with ray blight and the incidence of flowers with ray blight in four of six and three of six fields, respectively, whereas the Gompertz model provided the best fit in the remaining fields. Fungicides applied prior to mid-October (early spring) significantly reduced the area under disease progress curve (P < 0.001) for defoliation severity, the incidence of stems with ray blight, and the incidence of flowers with ray blight for epidemics at all field locations. This study provides information concerning the epidemiology of foliar disease and ray blight epidemics in pyrethrum and offers insight on how to best manage these diseases. © 2005 The American Phytopathological Society.

Item Details

Item Type:Refereed Article
Research Division:Biological Sciences
Research Group:Plant Biology
Research Field:Plant Pathology
Objective Division:Plant Production and Plant Primary Products
Objective Group:Horticultural Crops
Objective Field:Horticultural Crops not elsewhere classified
Author:Pethybridge, SJ (Dr Sarah Pethybridge)
Author:Hay, FS (Dr Frank Hay)
Author:Wilson, CR (Associate Professor Calum Wilson)
ID Code:30063
Year Published:2005
Web of Science® Times Cited:33
Deposited By:Agricultural Science
Deposited On:2005-08-01
Last Modified:2006-06-07
Downloads:0

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