Abstract
Oil palm cultivation in Ecuador is important for the agricultural sector. As a result of it, the country generates sources of employment in some of the most vulnerable zones; it contributes 0.89% of the gross domestic product and 4.35% of the agricultural gross domestic product. In 2017, a value of USD $252 million was generated by exports, and palm contributed 4.53% of the agricultural gross domestic product (GDP). It is estimated that 125,000 hectares of palm were lost in the Republic of Ecuador due to Red Ring Disease (RRD) and specifically Bud Rot (BR). The current study aimed to generate an early detection of BR and RRD in oil palm. Image acquisition has been performed using Remotely Piloted Aircraft System (RPAS) with Red, Green, and Blue (RGB) cannons, and multispectral cameras, in study areas with and without the presence of the given disease. Hereby, we proposed two phases. In phase A, a drone flight has been conducted for processing and georeferencing. This allowed to obtain an orthomosaic that serves as input for obtaining several vegetation indices of the healthy crop. The data and products obtained from this phase served as a baseline to perform comparisons with plantations affected by BR and RRD and to differentiate the palm varieties that are used by palm growers. In phase B, the same process has been applied three times with an interval of 15 days in an affected plot, in order to identify the symptoms and the progress of them. A validation for the diseases detection has been performed in the field, by taking Global Positioning System (GPS) points of the palms that presented symptoms of BR and RRD, through direct observation by field experts. The inputs obtained in each monitoring allowed to analyze the spatial behavior of the diseases. The values of the vegetation indices obtained from Phase A and B aimed to establish the differences between healthy and diseased palms, with the purpose of generating the baseline of early responses of BR and RRD conditions. However, the best vegetation index to detect the BR was the Visible Atmospherically Resistant Index (VARI).
Highlights
Diseases and pests that affect plants can harm a wide range of cash crops, resulting in significant yield loss [1,2,3]
The indices that made it possible to differentiate the palm from its environment, in the case of the materials of the phenological state 305, INIAP, CIRAD, and ASD were the Difference Vegetation Index (DVI) and Modified Triangular Vegetation Index (MTVI), for the phenological state 301, the Taisha material was used for the Normalized Difference Vegetation Index (NDVI), for Amazon and Unipalma the Burn area index (BAI)
With the BGNIR sensor, two baselines were obtained according to the conditions for the Green Normalized Difference Vegetation Index (GNDVI) and GVI indices
Summary
Diseases and pests that affect plants can harm a wide range of cash crops, resulting in significant yield loss [1,2,3]. Bud Rot (BR) is, economically, the most threatening disease for oil palm in Ecuador at present. According to the 2017 National Palm Census, the presence of BR has affected 148,433.8 ha, that represents 57.7% of all farms cultivated with oil palm, resulting in the loss of 50,000 direct and indirect jobs, as well as USD $200 million of economic damage of fresh fruit sales and USD $600 million in investments [9]. One of the symptoms produced by the aforementioned microorganism is the necrosis and collapse of the younger arrows, in addition to the fact that some young leaves sometimes acquire yellow coloration. In other zones with predisposal factors, such as Tumaco in southwest Colombia, the percentage of sick palms grew from 8.3% to 83% in two years (2007–2009), with the unproductive state of the sick palms becoming necessary to eradication and renewal [12]
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