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Sclerotinia crown rot, caused by Sclerotinia sclerotiorum and S. minor, is a prevalent disease in pyrethrum fields in Australia. Management involves fungicide applications during the rosette stage of plant development from autumn to early spring in fields approaching first harvest. However, estimates of crop damage and the efficacy of these tactics are poorly understood; therefore, plots were established in 86 pyrethrum fields in Tasmania, Australia during 2010 to 2012 to quantify these and to identify risk factors for disease outbreaks. On average, commercial management for Sclerotinia crown rot reduced disease incidence 43 to 67% compared with nontreated plots. There was a weak but significant relationship between relative increase in flower yield when fungicides were applied and the incidence of crown rot (R² = 0.09, P = 0.006), although the mean number of flowers produced was similar regardless of fungicide applications. Flower yield was positively associated with canopy density in spring (S = 0.39, P = 0.001). Moreover, canopy density in spring was linked by both direct and indirect effects to canopy density during autumn and winter which, in turn, were associated with planting date and previous rain events. Modeling canopy density and disease incidence in autumn correctly categorized disease incidence in spring relative to a threshold of 2% in 72% of fields. In a subset of 22 fields monitored over 2 years, canopy density in the autumn following the first harvest had a negative relationship with Sclerotinia crown rot incidence the preceding year (R² = 0.23, P = 0.006). On average, however, current commercial management efforts provided only small increases in flower yield in the current season and appear best targeted to fields with well-developed plant canopies and Sclerotinia crown rot present during early autumn.

Item Type:	Refereed Article
Research Division:	Agricultural and Veterinary Sciences
Research Group:	Horticultural Production
Research Field:	Horticultural Crop Protection (Pests, Diseases and Weeds)
Objective Division:	Plant Production and Plant Primary Products
Objective Group:	Horticultural Crops
Objective Field:	Horticultural Crops not elsewhere classified
UTAS Author:	Scott, JB (Dr Jason Scott)
UTAS Author:	Gent, DH (Dr David Gent)
UTAS Author:	Pethybridge, SJ (Dr Sarah Pethybridge)
UTAS Author:	Hay, FS (Dr Frank Hay)
ID Code:	87840
Year Published:	2014
Funding Support:	Australian Research Council (LP1010529)
Web of Science® Times Cited:	5
Deposited By:	Tasmanian Institute of Agriculture
Deposited On:	2013-12-10
Last Modified:	2017-11-06
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