Pethybridge Sarah J, Hay Frank, Esker Paul, Wilson Calum, Nutter Forrest W
Tasmanian Institute of Agricultural Research (TIAR), University of Tasmania, Burnie, Tasmania, 7320, Australia.
Department of Plant Pathology, Iowa State University, Ames 50011.
Plant Dis. 2007 Nov;91(11):1397-1406. 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 R 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.
在澳大利亚塔斯马尼亚州，对2年内在3个地点种植的除虫菊因叶斑病（Phoma ligulicola）导致的叶部病害进行了量化研究。为获得一系列叶斑病病害严重程度，对重复地块使用了防治叶斑病效果各异的杀菌剂进行处理。在春季（9月至12月）至少进行一次病害的目视评估和冠层反射率测量。目视评估包括在地面水平去除开花茎，从中获取落叶严重程度和带有叶斑病茎的发生率的测量数据。使用手持式多光谱辐射计在485、560、660、830和1650纳米波长下测量除虫菊冠层的阳光反射率。这些波长的测量数据还用于计算所有可能的反射率比值以及四个植被指数。通过线性回归分析描述了波段、反射率比值、植被指数和病害严重程度测量值之间的关系。几个波段、比值和植被指数与病害严重程度的目视测量值呈显著线性相关。最一致的关系，具有高R值和低变异系数值，随作物生长阶段随时间变化。830/560比值被确定为10月份茎高、落叶严重程度和每个茎上花朵数量的最佳预测指标。然而，近红外范围（830纳米）内的反射率和差值植被指数在11月份表现更优。使用辐射测量评估病害是非侵入性的，节省了病害评估时间，这在目视评估困难且需要破坏性采样（如除虫菊）的情况下至关重要。
