Nanobot Crop Guardian Swarm

A field of crop plants sits under threat from a spreading disease. Each infected plant leaks a biomarker that diffuses outward according to Fick's law, and a swarm of agricultural nanobots hunts it down the way chemotactic bacteria hunt a nutrient gradient — sampling local concentration, biasing their heading uphill, and dwelling to apply a precision dose the moment they arrive. Tune swarm size, gradient-following strength, per-bot payload capacity and how fast the biomarker plume spreads, then watch outbreaks shrink from red to healthy green as the swarm patrols, doses and cycles back to the depot to recharge.