Citrus greening disease (HLB) and citrus canker are diseases afflicting Florida citrus groves, causing financial losses through smaller fruits, blemishes, premature fruit drop and/or eventual tree death. Often, symptoms of these resemble those of other defects/infections. Early detection of HLB and canker via in-grove leaf inspection can permit more effective mitigation tactics and more intelligent management of groves. Autonomous, vision-based disease scouting in a grove offers a financial benefit to the Florida citrus industry. This study investigates the potential of hyperspectral reflectance imagery (HSI) for detecting and classifying these conditions in the presence of other, less consequential leaf defects. Both sides of leaves with visible symptoms of HLB, canker, zinc deficiency, scab, melanose, greasy spot, and a control set were collected and imaged with a line-scan hyperspectral camera. Spectral bands from this imagery were selected using two methods: an unsupervised method based on principal component analysis (PCA), and a supervised method based on linear discriminant analysis (LDA). Using the selected bands, the YOLOv8 network architecture was trained to classify each side of these leaves. LDA-selected bands from the back of the leaves yielded an overall classification accuracy of 84.23%. Leaves with HLB and zinc deficiency were classified most accurately, with F1 scores of 0.977 and 0.953, respectively. On the back side of the leaf, recall of melanose was significantly improved by using the LDA bands. These findings favor the use of supervised band selection for HSI-based in-grove disease detection.
Citrus Black Spot (CBS) disease, caused by the pathogenic fungus Phyllosticta citricarpa, presents a significant threat to citrus-growing regions, including Florida. Detecting CBS early is crucial, especially when trees don't yet show symptoms. This early stage provides an opportunity for orchard managers to take preventive measures and curb the disease's spread. In our study, we explore the CSI-D+ system, which combines cutting-edge fluorescence imaging technology with the YOLOv8 deep learning framework. We focus on identifying two CBS fungus variants, GC12 and GM33, commonly found on infected citrus leaves. Sample leaves were inoculated with varying concentration levels of the two variants and imaged by the CSI-D+ device. Impressively, the CSI-D+ system demonstrates exceptional discrimination abilities for discerning variant concentration levels. It achieves a notable mean accuracy of 96.97% for detecting the GC12 fungus, with an F1- score of 96.35% and a mean average precision (mAP) of 97.82%. Similarly, for the GM33 variant, the system maintains an average accuracy of 96.17%, an F1-score of 88.76%, and a mAP of 91.64%. The system offers promise as rapid, non-invasive tool for early CBS fungus spore detection on citrus leaves. By providing timely insights, it could empower effective intervention strategies, bolstering orchard resilience against this harmful fungus.
Citrus black spot (CBS) is a fungal disease caused by Phyllosticta citricarpa that poses a quarantine threat and can restrict market access to fruits. It manifests as lesions on the fruit surface and can result in premature fruit drops, leading to reduced yield. Another significant disease affecting citrus is canker, which is caused by the bacterium Xanthomonas citri subsp. citri (syn. X. axonopodis pv. citri); it causes economic losses for growers due to fruit drops and blemishes. Early detection and management of groves infected with CBS or canker through fruit and leaf inspection can greatly benefit the Florida citrus industry. However, manual inspection and classification of disease symptoms on fruits or leaves are labor-intensive and time-consuming processes. Therefore, there is a need to develop a computer vision system capable of autonomously classifying fruits and leaves, expediting disease management in the groves. This paper aims to demonstrate the effectiveness of convolutional neural network (CNN) generated features and machine learning (ML) classifiers for detecting CBS infected fruits and leaves with canker symptoms. A custom shallow CNN with radial basis function support vector machine (RBF SVM) achieved an overall accuracy of 92.1% for classifying fruits with CBS and four other conditions (greasy spot, melanose, wind scar, and marketable), and a custom Visual Geometry Group 16 (VGG16) with the RBF SVM classified leaves with canker and four other conditions (control, greasy spot, melanoses, and scab) at an overall accuracy of 93%. These preliminary findings demonstrate the potential of utilizing hyperspectral imaging (HSI) systems for automated classification of citrus fruit and leaf diseases using shallow and deep CNN-generated features, along with ML classifiers.
Citrus black spot (CBS) is a quarantine fungal disease caused by Phyllosticta citricarpa that can limit market access for fruit. It causes lesions on fruit surfaces and may lead to premature fruit drops, reducing yield. Leaf symptoms are uncommon for CBS, although the fungus reproduces in leaf litter. Similarly, citrus canker is another serious disease caused by the bacterium Xanthomonas citri subsp. citri (syn. X. axonopodis pv. citri) and leads to economic losses for growers from fruit drops and blemishes. Therefore, early detection and management of groves infected by CBS or canker via fruit and/or leaf inspection can benefit the Florida citrus industry. Manual inspection to classify disease symptoms on either fruits or leaves is a tedious and labor intensive process. Hence, there is need to develop computer vision system for autonomous classification of fruits and leaves that can speed up their management in fields. In this paper, we demonstrate the capability of convolution neural network (CNN)-based deep learning along with classical machine learning (ML) based computer vision algorithms to classify ‘Valencia’ orange fruit surfaces with CBS infection along with four other conditions and ‘Furr’ mandarin leaves with canker and four other conditions. Fruits with CBS and four other conditions (marketable, greasy spot, melanose and wind scar) were classified using a custom shallow CNN with SoftMax and RBF SVM at an overall accuracy of 89.8% and 92.1%, respectively. Similarly, a custom VGG16 network with SoftMax could classify canker leaves with F1-score of 85% and overall accuracy of 82% including other four conditions (control/healthy, greasy spot, melanose and scab). In addition, it was found that by replacing SoftMax with RBF SVM in the VGG16 network, the overall classification accuracy improved to 93% i.e., an increment of 11% points (13.41%). The preliminary findings reported in this paper demonstrate the capability of HSI system for automated citrus fruit and leaf disease classification using shallow and deep CNN generated features and ML classifiers.
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