Deep learning for apple leaf disease diagnosis: a comparative study with convolutional neural networks and transformers

Plant diseases pose a major threat to global food security, significantly reducing agricultural yields. Therefore, timely diagnosis of plant diseases can help prevent food losses and support economic stability. This study explores the use of eight Convolutional Neural Networks and two Vision Transformers for apple leaf disease diagnosis. The feature extraction layers of each model were modified to incorporate DropBlock layers, while preserving pretrained weights from the ImageNet dataset. Images from the Plant Pathology 2021 dataset were used to fine-tune the models for multi-label classification, targeting five disease categories and a healthy label. Three experiments were conducted to evaluate model performance on the test set. First, the ResNet50 model was used to determine optimal Dropout and DropBlock probabilities. Second, these parameters were applied across all models to identify those with the best performance. Finally, twenty-three Swarm Optimization Algorithms were used to optimize classifier thresholds, improving accuracy and F1-scores. A DropBlock probability of 0.05 and a Dropout probability of 0.2 yielded superior results. Among the models, SwinV2T attained an accuracy of 90.7%, while SwinV2S achieved the highest F1-score of 91.7%, slightly outperforming the ConvNeXtT and ConvNeXtS architectures. The results demonstrated the effectiveness of DropBlock regularization and optimized classifier thresholds, highlighting the superior performance of recent architectures and optimization algorithms over their older counterparts. These findings suggest that such networks hold substantial promise for accurately identifying and diagnosing apple leaf diseases.