Eiko Thiessen

Site-Specific Sensing for Fungicide Spraying

Especially in humid moderate climates, high yields require the application of fungicides. Its site-specific application based on the biomass of crops is state of the art. Yet this technique does not take into account that fungal infections in most cases start and spread out from small, initial spots within a field. So a sensing technique to detect these initially small infected spots would be of great importance for saving fungicides, for reducing damage to crops as well as to the environment and for allowing higher driving speeds in uninfected areas. Reflectance indices of visible and near-infrared light as well as indices of fluorescent light are candidates for detecting these spots.

Early optical detection of infection with brown rust in winter wheat by chlorophyll fluorescence excitation spectra

Abstract Puccinia recondita f. sp. tritici, the causative agent of brown rust disease is the reason for major yield losses in winter wheat plants (Triticum aestivum L.). Early detection of fungal infections would allow a specific fungicide application. Aim of the current study was to develop an automated and computer based device that differentiate infected and healthy plants non-invasively in an early stage of infection. To achieve the target an optical sensor device has been designed (“MultiDetExc”), which excites chlorophyll fluorescence in discrete wavelengths and detects the induced emissions. Wheat plants were infected artificially with brown rust in a climate chamber experiment to survey the capability of the instrument. The chlorophyll fluorescence excitation spectra of whole wheat plants were measured on several days after infection. As reference methods, HPLC and qPCR analysis were included in the current study to measure the polyphenol content of the leaves and the level of infection. The recently developed sensor device is an efficient technique to differentiate the infected and not infected wheat plants as soon as four days after inoculation. The measured fluorescence quotients correlate high positive with the polyphenol contents and the relative amount of fungal DNA. An untreated healthy control was measured parallelly, in order to associate the increased synthesis of polyphenols to the fungal infection definitely.

Sensing of Crop Properties

Sensing of crops by visible and infrared reflectance allows estimating the chlorophyll concentration within leaves as well as the leaf-area-index. The product of the chlorophyll concentration within leaves and the leaf-area-index supplies the chlorophyll content per unit field area. Recording this criterion repeatedly during the season provides reliable estimates of the site-specific yield potential as based on past growing conditions.