Predicting Leaf Rust Infection Rate in Winter Wheat Using Normalized Difference Vegetation Index.

Leaf rust infection causes significant yield losses in winter wheat. Selection of rust resistant lines calls for efficient screening of the rust infection rate for a large number of wheat genotypes under field conditions. We used an ACS-430 Crop Circle sensor mounted on a ground-based phenotyping cart to test if the presence of leaf rust in winter wheat is reflected in measured vegetation indices. The field scans were conducted multiple times during the growing seasons of 2017 and 2018 at the Castroville Wheat Nursery, Castroville, Texas. About 1000 plots (dimension 4.6 × 1.5 m²) were scanned in 2017 and 500 plots scanned in 2018. Linear regression equations were developed to relate the leaf rust infection rate on flag leaves with the derived vegetation indices from the canopy reflectance measured at the red and far red wavelengths. The results show that canopy reflectance at red-edge band can to some extent reflect the presence of leaf rust in winter wheat; however, the relationship is weaker after flowering with increased leaf aging.