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Title: NDVI to detect sugarcane aphid injury to grain sorghum

Author
item Elliott, Norman - Norm
item BACKOULOU, GEORGES - Oklahoma State University
item BREWER, MICHAEL - Texas Agrilife Research
item GILES, KRISTOPHER - Oklahoma State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2014
Publication Date: 6/5/2015
Publication URL: http://handle.nal.usda.gov/10113/61763
Citation: Elliott, N.C., Backoulou, G.F., Brewer, M.J., Giles, K.L. 2015. NDVI to detect sugarcane aphid injury to grain sorghum. Journal of Economic Entomology. 108(3):1452-1455.

Interpretive Summary: Multispectral remote sensing has potential to provide quick and inexpensive information on insect pest status in agricultural crops. The purpose of this research was to describe a study conducted to determine if injury caused by sugarcane aphid to sorghum plants in fields of grain sorghum could be detected using multispectral remote sensing from a fixed wing aircraft. Twenty six commercial grain sorghum fields were selected and rated for the level of injury to sorghum plants in the field caused be sugarcane aphid. Plant growth stage was also measured. Reflected light in the visible red and near infrared parts of the spectrum were used to calculate an index commonly called the normalized differenced vegetation index (NDVI). NDVI is useful for measuring stress to growing plants. The correlation between NDVI and plant injury rating was negative, as was the correlation between NDVI and plant growth stage. These significant correlations indicated negative linear relationships between NDVI and plant injury and plant growth stage. The correlation between plant injury rating and plant growth stage was positive and significant indicating that the two variables had a positive linear association, with injury severity increasing with increasing plant maturity. The partial correlation NDVI to plant injury rating was negative and significant indicating that NDVI decreased with increasing plant injury apart from the association of injury with plant growth stage. We demonstrated that remotely sensed imagery acquired from grain sorghum fields using a multi-spectral imaging system was sensitive to the extent of injury to sorghum plants in fields caused by sugarcane aphid. The most important contribution of this study was demonstrating that multi-spectral data acquired by a relatively inexpensive airborne imaging system was capable of detecting sugarcane induced injury in production sorghum fields. The result indicated that airborne multi-spectral imaging as a tool for monitoring sorghum fields for sugarcane aphid infestation is feasible.

Technical Abstract: Multispectral remote sensing has potential to provide quick and inexpensive information on sugarcane aphid, Melanaphis sacchari (Zehntner), pest status in sorghum fields. The purpose of this report is to describe a study conducted to determine if injury caused by sugarcane aphid to sorghum plants in fields of grain sorghum could be detected using multispectral remote sensing from a fixed wing aircraft. A study was conducted in commercial grain sorghum fields in the Texas Gulf Coast in June 2014. Twenty six commercial grain sorghum fields were selected and rated for the level of injury to sorghum plants in the field caused be sugarcane aphid. Plant growth stage ranged from 5.0 (watery ripe) to 7.0 (hard dough) among fields with a mean growth stage of 6.3; and plant injury rating from sugarcane aphid infestation ranged from 1.0 (little or no injury) to 4.0 (> 40% of plants displaying injury) among fields with a mean of 2.3. NDVI is calculated from light reflectance in the red and near-infrared wavelength bands in multispectral imagery and is a common index of plant stress. High NDVI indicates low levels of stress and low NDVI indicates high stress. NDVI ranged from -0.07 to 0.26 among fields with a mean of 0.06. The correlation between NDVI and plant injury rating was negative and significant, as was the correlation between NDVI and plant growth stage. The negative correlation of NDVI with injury rating indicated that plant stress increased with increasing plant injury. Reduced NDVI with increasing plant growth probably resulted from reduced photosynthetic activity in more mature plants. The correlation between plant injury rating and plant growth stage was positive and significant indicating that plant injury from sugarcane aphid increased as plants matured. The partial correlation of NDVI with plant injury rating was negative and significant indicating that NDVI decreased with increasing plant injury after adjusting for its association with plant growth stage. We demonstrated that remotely sensed imagery acquired from grain sorghum fields using a multi-spectral imaging system was sensitive to injury to sorghum plants caused by sugarcane aphid.