Suitability of the MODIS-NDVI Time-Series for a Posteriori Evaluation of the Citrus Tristeza Virus Epidemic

Daniela Vanella,Matilde Tessitori,Juan Miguel Ramírez-Cuesta,Simona Consoli

doi:10.3390/rs12121965

Abstract

The technological advances of remote sensing (RS) have allowed its use in a number of fields of application including plant disease depiction. In this study, an RS approach based on an 18-year (i.e., 2001–2018) time-series analysis of Normalized Difference Vegetation Index (NDVI) data, derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and processed with TIMESAT free software, was applied in Sicily (insular Italy). The RS approach was carried out in four orchards infected by Citrus tristeza virus (CTV) at different temporal stages and characterized by heterogeneous conditions (e.g., elevation, location, plant age). The temporal analysis allowed the identification of specific metrics of the NDVI time-series at the selected sites during the study period. The most reliable parameter which was able to identify the temporal evolution of CTV syndrome and the impact of operational management practices was the “Base value” (i.e., average NDVI during the growing seasons, which reached R2 values up to 0.88), showing good relationships with “Peak value”, “Small integrated value” and “Amplitude”, with R2 values of 0.63, 0.70 and 0.75, respectively. The approach herein developed is valid to be transferred to regional agencies involved in and/or in charge of the management of plant diseases, especially if it is integrated with ground-based early detection methods or high-resolution RS approaches, in the case of quarantine plant pathogens requiring control measures at large-scale level.

Highlights

The adoption of remote sensing (RS) approaches is gaining special relevance to monitor, quantify and map vegetation dynamics resulting from life-cycle patterns, climatic conditions, photosynthetic activity and plant diseases [1,2]
The limited temporal availability of the images does not permit a clear picture of the on-site Citrus tristeza virus (CTV)-related dynamics
Results derived from TIMESAT analysis reflected a stable pattern of the seasonal parameters in CS1, which can be related to the in situ conditions influenced both by the CTV effects on plants and by the adoption of spotted mitigation actions such as eradication of infected plants and replanting with trees grafted on tolerant rootstocks in order to prevent economic damages since 2002 (Figure 4)

Summary

Introduction

The adoption of remote sensing (RS) approaches is gaining special relevance to monitor, quantify and map vegetation dynamics resulting from life-cycle patterns, climatic conditions, photosynthetic activity and plant diseases [1,2]. Plant pathogens cause damage to crops, quantifiable in direct and indirect costs. In addition to the direct costs, quantified as yield losses, in the case of virus diseases and consequent quarantine plan, the indirect costs (i.e., plant protection treatments, environmental impact of pesticides, replacement of plants and loss of biodiversity) find the major item being prevention costs with a strong economic and social impact for the community. In situ monitoring approaches for plant health have made tremendous progress, but they are intensive and often integrate subjective indicators. RS bridges the gaps of these limitations by monitoring indicators of plant health on different spatio-temporal scales and in a cost-effective, rapid, repetitive and objective manner [3]. Visible/near-infrared (VIS/NIR) and thermal (TIR) imaging techniques have been applied for detecting the stress condition of plants infected by pathogens, such as fungi [5,6], bacteria [7] and viruses, e.g., tobacco mosaic virus [8], grape leaf roll-associated virus-3 [9] or sugarcane yellow leaf virus [10]

Methods

Results

Conclusion