Assessing spatio-temporal patterns of sugarcane aphid (Hemiptera: Aphididae) infestations on silage sorghum yield using unmanned aerial systems (UAS)

Authors: ZHANG, JING - University Of Georgia; MALESKI, JEROME - University Of Georgia; SCHWARTZ, BRIAN - University Of Georgia; DUNN, DUSTIN - University Of Georgia; MAILHOT, DANIEL - University Of Georgia; Ni, Xinzhi; Harris-Shultz, Karen; Knoll, Joseph - Joe; TOEWS, MICHAEL - University Of Georgia

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2021
Publication Date: 5/2/2021
Citation: Zhang, J., Maleski, J., Schwartz, B., Dunn, D., Mailhot, D., Ni, X., Harris-Shultz, K.R., Knoll, J.E., Toews, M. 2021. Assessing spatio-temporal patterns of sugarcane aphid (Hemiptera: Aphididae) infestations on silage sorghum yield using unmanned aerial systems (UAS). Crop Protection. 146: 105681. https://doi.org/10.1016/j.cropro.2021.105681.
DOI: https://doi.org/10.1016/j.cropro.2021.105681

Interpretive Summary: Very few studies have used unmanned aerial system-based imagery to assess sugarcane aphid damage in sorghum variety trials to identify the best performing hybrids for growers to use. Most of the previous studies focused on individual characteristic of sorghum development, yield, and pest resistance. Previous studies also noted that it is challenging to detect sugarcane aphid damage on sorghum plants as indicated by certain parameters until the damage is severe. The current two-year research in 2019 and 2020 quantified sugarcane aphid damage on silage sorghum varieties utilized two platforms equipped with either a red, green, and blue light camera, or a multispectral camera, respectively. In addition, a new workflow scheme was developed including the unmanned aerial system-based image processing, raster calculation, digital terrain model and canopy height model generation, image extraction of sorghum plants, and tabular dataset generation from zonal statistics for further statistical analyses. The results also demonstrated that the two platforms and the expanded unmanned aerial system-based measurements was correlated with the labor-intensive ground measurements. The findings from the study demonstrated that this technique can be used for high throughput phenotyping in both hybrid performance and germplasm development. The high throughput phenotyping can improve the capability of entomologists and sorghum breeders to simultaneously evaluate multiple traits (such as, aphid and disease resistance, drought tolerance, and good yield potential).

Technical Abstract: In the U.S. since 2013, the sugarcane aphid is a perennial pest to all types of sorghum. Rating sugarcane aphid population density, plant damage, and other traits in sorghum requires a large amount of labor and ratings, especially damage ratings, may vary by evaluator. Thus, Unmanned Aerial Systems (UAS)–based imagery may be exceedingly useful to more accurately quantify the effects on sorghum caused by sugarcane aphids. This study quantified the dynamic nature of sugarcane aphid infestations on silage sorghum varieties using UAS-based imagery data, and demonstrated the UAS-based measurements correlated to ground measurements. Two UAS platforms equipped with RGB (red, green, and blue) and multispectral cameras respectively were used to evaluate the silage sorghum variety trials during the growing seasons of 2019 and 2020. For the purpose of high throughput phenotyping in sorghum breeding, a new workflow scheme was developed including UAS image processing, raster calculation, DTM (digital terrain model) and CHM (canopy height model) generation, image extraction of sorghum plants, and tabular dataset generation from zonal statistics for further statistical analyses. Ground-based measurements included aphid sampling, aphid damage ratings, plant height, and biomass yields. The normalized difference red edge index (NDRE) and canopy cover collected by the UAS showed negative linear relationship with aphid damage ratings in both trials (R2 = 0.55 – 0.64). In addition to assessing spatial differences among the varieties in 2019, temporal change in both NDRE and canopy cover from the baseline sampling date in 2020 better estimated aphid damage, R2 of 0.68 and 0.79 respectively, than using the spatial difference of NDRE (R2 = 0.55) and canopy cover (R2 = 0.57) before harvest. Plant height (R2 = 0.84, RMSE = 0.16 m) can be estimated with efficiency and precision using UAS-derived measurements during high throughput phenotyping of sorghum. Fresh yield estimates for the primary harvests were consistent in both years, but green yield estimates differed among harvests and need to be improved. Future development of UAS-based high throughput phenotyping would benefit from increased temporal resolutions of growth parameters and vegetation indices throughout a growing season.