Training convergence of CNN and LSTM-BiLSTM
Fig 2-3 show stable training for both models. The CNN accuracy increases from 10-20% to 65-75% (500-750 iterations) while loss drops from 12.8 to <2 by 60 iterations, indicating strong texture learning. The LSTM-BiLSTM rises from 5-10% to 50-65% (~700), peaking >70%, with loss reaching ~0.9 and a brief spike near 420.
Confusion matrix of the hybrid CNN-LSTM-BiLSTM model showing class-wise prediction performance and misclassification patterns
Fig 4 confusion matrix assesses the hybrid CNN-LSTM-BiLSTM across 10 leaf classes. Maize Brown Spot achieves 17 correct predictions (56.7%), mainly misclassified as Maize Rust. Maize Healthy is perfectly identified (20/20). Classes such as Potato Early Blight and Soybean Mosaic Virus show moderate accuracy due to visual overlap, confirming mixed spatial–temporal discrimination.
Class-wise precision, recall and f1-score evaluation of the hybrid CNN-LSTM-BiLSTM model for multi-crop disease classification
Fig 5 (Precision-Recall-F1) summarizes class-wise performance of the hybrid model. Maize Brown Spot shows moderate precision (0.57) with high recall (0.85), yielding an F1-score of 0.68. Maize Healthy performs strongly (precision 0.67, recall 1.00, F1 0.80). Potato Early Blight records lower scores due to confusion with healthy leaves. Soybean SBS achieves the highest F1 (0.88), indicating robust discrimination for visually distinct symptoms.
Prediction confidence distribution of the hybrid CNN-LSTM-BiLSTM model for crop disease classification
Fig 6 presents the prediction-confidence distribution of the hybrid CNN–LSTM–BiLSTM model. Most outputs cluster in three bands: 0.35-0.45, 0.55-0.65 and 0.90-0.92. Low confidence (0.35-0.45) corresponds to visually subtle diseases such as early blight and mosaic virus, while the highest confidence (0.90-0.92) aligns with distinct classes like Soybean SBS and Soybean Pod Mottle. Overall, the histogram indicates robust performance with strong mid-confidence peaks and high certainty for clearly separable symptoms.
Training convergence of CNN and LSTM-BiLSTM models
Fig 7-8 indicate stable learning. The CNN accuracy rises from 10-20% to 60-75% by ~300 iterations, with loss dropping from 13.2 to <1.0 after ~200, showing strong spatial feature extraction and occasional >80% peaks. The LSTM–BiLSTM improves from 8-15% to >60% (often >80%), while loss falls to ~1.5 by 200; a spike near 650 reflects ambiguous batches but quickly stabilizes.
Evaluation of hybrid CNN + RNN classifier using class-wise confusion matrix
Fig 9 shows the confusion matrix for the CNN+RNN hybrid model. The model accurately classifies 20 samples of Maize Brown Spot (87.0% accuracy), while other categories like Potato Early Blight exhibit lower accuracy due to feature overlap with healthy leaves. Overall, the confusion matrix highlights the model’s strong feature extraction and temporal reinforcement, enabling it to accurately assess disease patterns in a variety of crops.
Class-wise precision, recall and F1-score analysis of the hybrid CNN-RNN model
Fig 10 compares CNN+RNN class-wise metrics. Maize Brown Spot performs well (precision/recall/F1 = 0.74). Potato Early Blight fails completely (precision = 0, recall = 0), indicating severe confusion. Soybean SBS achieves perfect scores (1.00/1.00/1.00). Overall, results show strong detection for distinct symptoms but weakness with overlapping patterns.
Prediction confidence distribution of the CNN-RNN hybrid model for multi-class disease detection
Fig 11 shows the Hybrid CNN+RNN confidence distribution across 10 disease classes. Most predictions cluster at 0.38-0.42 (~90), reflecting moderate certainty where spatial lesions are captured but temporal cues remain ambiguous (
e.
g., Maize Rust, Early Blight, Soybean Mosaic Virus). Low-confidence outputs at 0.30-0.32 (~40) suggest harder cases (mild chlorosis) needing better features/augmentation. Higher confidence at 0.50-0.55 (~30-35) aligns with clearer patterns (Potato late blight, soybean pod mottle). A small high-confidence peak at 0.80-0.85 (~18) corresponds to distinctive classes like Soybean SBS and Maize Brown Spot.
Comprehensive image processing workflow for maize brown, maize healthy, maize rust, potato early blight, potato healthy, potato late blight, soybean healthy, soybean mosaic virus, soybean pod mottle, soybean sbs spot detection and severity quantification
Fig 12-14 depict the full workflow for 10 leaf classes, showing segmentation, defect localization and edge enhancement (original image, binary mask, segmented leaf, defect mask, red overlay and Canny edges) to link symptoms with defect percentage. Maize Brown Spot is most severe (87.93% necrotic lesions), while Maize Rust is mild (5.43%); Maize Healthy defects (7.21%) mainly reflect illumination artifacts. Potato Early Blight (41.86%) and Late Blight (45.14%) show major necrosis, whereas Potato Healthy is near-zero (0.29%). Soybean Mosaic Virus (5.63%), Pod Mottle (11.41%) and SBS (30.20%) vary in severity; Soybean Healthy is 0.00%. Table 1 summarizes symptoms and defects (0.00-87.93%), supporting interpretable, reliable Hybrid CNN-LSTM-BiLSTM detection.
Heatmap of leaf defect severity across ten crop disease categories
Fig 15 presents a severity heatmap for 10 crop diseases, where darker colors indicate higher defect percentage. Maize brown spot shows the highest damage (~85-90%), while Maize Healthy remains minimal (0-5%). Potato Early and Late Blight exhibit high severity (40-50%). Soybean SBS shows moderate defects (25-35%), validating pipeline effectiveness.
Table 2 compares twelve plant disease detection methods by algorithm, dataset and accuracy against the proposed Hybrid CNN-LSTM-BiLSTM. Unlike prior work, our approach integrates segmentation and defect-percentage quantification with deep spatial–temporal learning, achieving stronger multi-class recognition, improved feature separability and early-stage severity estimation for precision agriculture applications.