Looks like this University of New Hampshire ag research team is using an APM-powered ArduCopter for their research into the use of drones to spot crop disease. Excerpt from the Modern Farmer article:
“When you think about apple production now, a grower needs to walk through his orchard every day to make sure he sees any new insect pests or any new disease pests that come into an orchard,” says plant pathologist Kirk D. Broders, an assistant professor at UNH. “But when you’re talking about a 10, 20, 100-acre orchard, your ability to do that on a daily basis is almost impossible.”
But it is possible with a small unmanned aerial vehicle (UAV), or drone, carrying an infrared camera that takes multispectral images of the orchard. A computer program crunches the wavelengths in each pixel, making it possible to hone in on colors and temperatures – and locate apple scab.