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Quantifying loss caused by Ray Blight Disease in Tasmanian pyrethrum fields


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Pethybridge, SJ, Esker, PD, Dixon, P, Hay, FS, Groom, T, Wilson, CR and Nutter, FW 2007 , 'Quantifying loss caused by Ray Blight Disease in Tasmanian pyrethrum fields' , Plant Disease, vol. 91, no. 9 , pp. 1116-1121 , doi: 10.1094/PDIS-91-9-1116.

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The efficacy of newly implemented fungicide recommendations on reducing the intensity of ray
blight disease caused by Phoma ligulicola to achieve site-specific attainable yield potentials in Tasmanian pyrethrum fields was quantified over two seasons in 46 and 51 fields during the 2003 and 2004 growing seasons, respectively. Disease intensity and yield in two plots (10 ×24 m), one following the commercial fungicide protocol recommendations and the second receiving no fungicide, were assessed in each pyrethrum field. The commercial fungicide protocol consisted of one application of azoxystrobin at 150 g a.i./ha, followed by two applications of a tank mixture of difenoconazole at 125 g a.i./ha and chlorothalonil at 1,008 liters a.i./ha at 14- to 21-day intervals. This program resulted in significant decreases in defoliation severity and the incidence of stems and flowers with ray blight, and increases in the height of stems and number of flowers produced per stem in October and November. In plots receiving the commercial fungicide protocol, the dry weight of flowers was increased by 76 and 68% in 2003 and 2004, respectively.
Moreover, pyrethrin yield increased by 81 and 78% when the commercial fungicide protocol was used compared with the nontreated plots. Tobit regression was used to examine the relationships and thresholds among disease intensity measures (defoliation severity, stem severity, and
incidence of flowers with ray blight) assessed just prior to harvest. This regression utilized a left censored regression model to define subminimal thresholds, as none of the disease intensity measures could be less than 0. Defoliation severity had a threshold of 35.3% before stem severity linearly increased and a threshold of 38.2% before the incidence of flowers with ray blight linearly increased. Finally, the threshold for stem severity was 13.7% before the incidence of flowers with ray blight linearly increased. These thresholds can be used to assist growers in making disease management decisions with the objective of minimizing loss of flowers by maintaining defoliation severity below the critical point at which the incidence of flowers with ray blight begins to linearly increase.

Item Type: Article
Authors/Creators:Pethybridge, SJ and Esker, PD and Dixon, P and Hay, FS and Groom, T and Wilson, CR and Nutter, FW
Keywords: disease loss, yield loss
Journal or Publication Title: Plant Disease
Publisher: American Phytopathological Society
ISSN: 0191-2917
DOI / ID Number: 10.1094/PDIS-91-9-1116
Additional Information:

© 2007 The American Phytopathological Society

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