Recognition of grape leaf diseases and mobile application based on transfer learning

Abstract: Pests and diseases have posed a severe threat to the production of grapes, causing irreversible damage on the growth cycle of grapes. The treatments vary significantly in the types of grape diseases. Therefore, it is highly demanding to detect the diseases of grapes timely, while accurately identify the types of diseases to avoid the spread of diseases. In the early days, the diseases of grapes were mainly identified by experienced grape and pest experts recognizing the grape leaves manually, which is time-consuming and laborious. It is necessary to develop a grape disease recognition using computer science technology. Convolutional Neural Network (CNN) has been used to automatically recognize agricultural pests in the field of Artificial Intelligence (AI) in recent years. However, the general CNN cannot be well trained to achieve high accuracy, due mainly to few large datasets of diseased grape leaves. In this study, a new recognition network of grape leaf disease was proposed using CNN. Transfer learning and data enhancement were also applied for the new network to enlarge the small dataset of grape leaves. The new network was named Grape-VGG-16 (GV for short) using VGG-16 network (one of the most classical CNN). GV generally contained 5 convolutions, 2 full connection 1 flatten, 1 dropout, and 1 SoftMax layer. The knowledge was first learned from the ImageNet image dataset using transfer learning, and then be transferred to the GV in the disease recognition of grape leaf. The output number was modified to 4 for the last fully connected layer using fine tuning, representing the 4 types of grapes leaves (healthy, brown spot, wheel spot, and black rot). A TensorFlow framework was selected to verify the network in the experiments using Python programming language. 300 images were collected for each leaf category (the total number of images was 1200), 250 of which were randomly selected as the training set, and 50 of which as the testing set. Then the dataset of images was augmented under the operations, such as random rotation, random horizontal and vertical translation, as well as horizontal flipping on the image. Finally, the augmented dataset was used to train the GV network, which was uniformly scaled to 224×224 pixels. 18 groups of experiments were performed on a computing server with Nvidia GPU using a combination of three learning (new learning, transfer learning with training the full connection layer, as well as transfer learning with training both the last convolution and full connection layer), two dataset with/without augmentation, and three learning rates (0.01, 0.001, and 0.000 1). The experimental results demonstrated that: 1) Transfer learning improved the model accuracy, while shortened the convergence time of the model; 2) Data augmentation greatly increased the diversity of data, while effectively alleviated the over-fitting. Consequently, the GV network achieved an overall recognition accuracy of 96.48% under both transfer learning and data augmentation. The recognizing accuracies of healthy leaves, brown spot, wheel spot and black rot were 98.04%, 98.04%, 95.83%, and 94.00%, respectively. The GV network was also embedded in the mobile application, and then deployed on the mobile terminal, for the detection and recognition of grape leaf diseases in the field. The finding can offer a potential promising reference for the intelligent diagnosis of grape leaf diseases in fruit production.