Human vs. Machine, the Eyes Have It. Assessment of Stemphylium Leaf Blight on Onion Using Aerial Photographs from an NIR Camera

Mary Ruth Mcdonald,Cyril Selasi Tayviah,Bruce D Gossen

doi:10.3390/rs14020293

Mary Ruth Mcdonald, Cyril Selasi Tayviah + Show 1 more

Open Access

https://doi.org/10.3390/rs14020293

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Journal: Remote Sensing	Publication Date: Jan 9, 2022
Citations: 3	License type: CC BY 4.0

Affiliation: University of Guelph

Abstract

Aerial surveillance could be a useful tool for early detection and quantification of plant diseases, however, there are often confounding effects of other types of plant stress. Stemphylium leaf blight (SLB), caused by the fungus Stemphylium vesicarium, is a damaging foliar disease of onion. Studies were conducted to determine if near-infrared photographic images could be used to accurately assess SLB severity in onion research trials in the Holland Marsh in Ontario, Canada. The site was selected for its uniform soil and level topography. Aerial photographs were taken in 2015 and 2016 using an Xnite-Canon SX230NDVI with a near-infrared filter, mounted on a modified Cine Star—8 MK Heavy Lift RTF octocopter UAV. Images were taken at 15–20 m above the ground, providing an average of 0.5 cm/pixel and a field of view of 15 × 20 m. Photography and ground assessments of disease were carried out on the same day. NDVI (normalized difference vegetation index), green NDVI, chlorophyll index and plant senescence reflective index (PSRI) were calculated from the images. There were differences in SLB incidence and severity in the field plots and differences in the vegetative indices among the treatments, but there were no correlations between disease assessments and any of the indices.

Highlights

Aerial photographs taken from a unmanned aerial vehicles (UAVs) platform are increasingly being used in routine agricultural assessments, such as weed identification and quantification, and crop staging [1]
Stemphylium leaf blight incidence and leaf dieback were higher in August relative to July in both years
Onion crops with higher leaf dieback caused by Stemphylium leaf blight were expected to have lower normalized difference vegetative index (NDVI), green NDVI (GNDVI), and CI values and higher plant senescence reflective index (PSRI) values compared to onion crops with lower incidence

Summary

Introduction

Aerial photographs taken from a UAV platform are increasingly being used in routine agricultural assessments, such as weed identification and quantification, and crop staging [1]. Detection and identification of diseases using aerial reconnaissance, especially in high-value crops, could facilitate disease management and reduce the risk of subsequent losses in crop yield and quality. To date, this technology has only rarely been used in assessments of plant diseases [4,5,6,7,8,9]. Much of the production in eastern North America occurs on soils that are extremely high in organic matter (45–80% organic matter, known as muck soils) Many of these sites are drained marshes, where the deep, rich, uniform soils and availability of irrigation are highly suited to onion production, and favor fungal diseases, such as Stemphylium leaf blight on onion [11]

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