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Canopy Reflectance as a Measure of Disease in Tall Fescue

Michigan State Univ., 102 Pesticide Res. Center, East Lansing, MI 48824
Dep. of Plant Pathology, 1109 Experiment Street, Georgia Station, Griffin, GA 30223-1797
Univ. of Georgia, Dep. of Plant Pathology, Miller Plant Sciences Bldg., Athens, GA 30606

^* Corresponding author (greende2{at}pilot.msu.edu).

Measurement of changes in canopy reflectance of tall fescue (Festuca arundinacea Schreb.), which result from deterioration of tissues caused by disease organisms, is a potential unbiased method for quantifying disease. Canopy reflectance in eight spectral bands between 430 and 840 nm and 18 vegetation indices derived from the spectral bands were regressed against visual severity estimates of Rhizoctonia blight, caused by Rhizoctonia solani Kühn, and gray leaf spot, caused by Pyricularia grisea (Cooke) Sacc. Reflectance within the 810-nm band exhibited the strongest relationship (19% r² 63%) with visual severity estimates of Rhizoctonia blight and gray leaf spot. Reflectance in the visible or near infra-red wavelengths was similar to tall fescue blighted by either fungal pathogen. A significant (P 0.05) negative linear relationship was observed between canopy reflectance in the 810-nm band and the severity of either Rhizoctonia blight or gray leaf spot. As Rhizoctonia blight decreased with increases in the application rate of the fungicide flutolanil (N-[3-(1-methylethoxy)-phenyl]-2-(trifluoromethyl)benzamide) and the proportion of a resistant cultivar in tall fescue blends, canopy reflectance in the 810-nm band increased. However, models based on canopy reflectance had twice as much unexplained variability than models based on visual severity estimates of Rhizoctonia blight. Factors other than disease influenced variability in reflectance of light from tall fescue canopies.

Received for publication February 8, 1998.

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