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Use of a Multispectral Radiometer for Noninvasive Assessments of Foliar Disease Caused by Ray Blight in Pyrethrum


Pethybridge, SJ and Hay, FS and Esker, PD and Wilson, CR and Nutter, FW, Use of a Multispectral Radiometer for Noninvasive Assessments of Foliar Disease Caused by Ray Blight in Pyrethrum, Plant Disease , 91, (11) pp. 1397-1406. ISSN 0191-2917 (2007) [Refereed Article]

DOI: doi:10.1094/PDIS-91-11-1397


Foliar disease due to ray blight (Phoma ligulicola) in pyrethrum was quantified at three locations over 2 years in Tasmania, Australia. To obtain a range of ray blight disease intensities, replicated plots were treated with fungicides that varied in efficacy to control ray blight. Visual disease assessments and measurement of canopy reflectance were made at least once during spring (September through December). Visual assessments involved removal of flowering stems at ground level from which measurements of defoliation severity and the incidence of stems with ray blight were obtained. Reflectance of sunlight from pyrethrum canopies was measured at 485, 560, 660, 830, and 1,650 nm using a handheld multispectral radiometer. Measurements from these wavelengths also were used to calculate all possible reflectance ratios, as well as four vegetative indices. Relationships between wavelength bands, reflectance ratios, vegetative indices, and disease intensity measures were described by linear regression analyses. Several wavelength bands, ratios, and vegetative indices were significantly related in a linear fashion to visual measures of disease intensity. The most consistent relationships, with high R2 and low coefficients of variation values, varied with crop growth stage over time. The ratio 830/560 was identified as the best predictor of stem height, defoliation severity, and number of flowers produced on each stem in October. However, reflectance within the near-infrared range (830 nm) and the difference vegetative index was superior in November. The use of radiometric assessment of disease was noninvasive and provided savings in disease assessment time, which is critical where visual assessment is difficult and requires destructive sampling, as with pyrethrum. © 2007 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
UTAS Author:Pethybridge, SJ (Dr Sarah Pethybridge)
UTAS Author:Hay, FS (Dr Frank Hay)
UTAS Author:Wilson, CR (Professor Calum Wilson)
ID Code:40578
Year Published:2007
Funding Support:Australian Research Council (LP0211065)
Web of Science® Times Cited:12
Deposited By:Agricultural Science
Deposited On:2007-08-01
Last Modified:2009-08-26

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