Vision normalizing flows for the probability-informed detection of banana diseases from in-field images

Banana diseases impose severe production losses in tropical smallholder farming systems, yet accurate in-field visual diagnosis remains difficult because symptom expression varies across cultivars and growth stages and several diseases produce morphologically overlapping foliar signs. We therefore developed a probabilistic image-recognition framework for detecting five economically important banana diseases from in-field photographs without disease-specific fine-tuning of the vision backbone.

Frozen 1,152-dimensional embeddings were extracted from the DINOv3 vision foundation model and coupled with a conditional normalizing flow. The model was trained on four publicly available datasets comprising approximately 95,000 images across eight classes spanning diseased banana plants, healthy tissue, non-banana vegetation, and general natural imagery.

On an independent test set, the model achieved F1 scores exceeding 0.98, average precision values of 0.9678-0.9998, and AUROC values of 0.9967-0.9998 across all five diseases evaluated as binary detection problems. Multi-class accuracy was nearperfect, with limited confusion between Yellow Sigatoka and Black Sigatoka. Because the normalizing flow estimates explicit conditional probability densities rather than decision boundaries, two complementary log-likelihood ratios were derived: a disease ratio comparing each disease class against healthy banana, and a plant ratio comparing banana against non-banana imagery.

Together, these likelihood ratios define an interpretable two-dimensional diagnostic space that simultaneously quantifies evidence for disease presence and image relevance, cleanly separating diseased plants, healthy plants, and out-ofdistribution images while flagging uncertain predictions for confirmatory testing. Batched inference costs 6.4 ms per image on a single TPU core, supporting deployment at surveillance-programme scale and providing a scalable, uncertainty-aware diagnostic tool for smallholder farming systems.