Optical Devices Evaluation for Diagnosis of Plasmopara viticola on Vine

Remote sensing (RS) is the most widely adopted technique for crop monitoring in precision viticulture (PV). Recent research looks at the development of proximal sensing technologies alternative to RS. The present work considers the possible use of proximal sensing optical devices for diagnosis in vineyard; in particular, we evaluated the GreenSeeker RT100 and the Crop Circle (two commercial optical sensors) in detecting different levels of grapevine downy mildew symptoms. The analysis was conducted on vine leaves that had been picked from plants of cv. Cabernet Franc infected by Plasmopara viticola. Leaves were divided into homogeneous infection classes and then analyzed through the optical devices and a portable Vis/NIR (visible/near infrared) spectrophotometer used as tester. Data showed a linear relation between the percentage of symptomatic leaf area and normalized difference vegetation index NDVI calculated through the two optical sensors (RPP 2 = 0.708 for GreenSeeker; R 2 = 0.599 for Crop Circle; R 2 = 0.950 for the spectrophotometer). The regression obtained for GreenSeeker is more significant than the regression obtained for Crop Circle. This fact suggests a greater capability of GreenSeeker than Crop Circle in detecting different disease levels and its possible use in diagnosis application in vineyard.