That really brings up an interesting thought on iron, one of the main building blocks in our blood cells. After seeing the difference in plants disease, heat and pest resistance, when growing with calcium and building thick cell walls, vs nitrate fed plants. It always makes me think twice about some old wives tales. It also makes me think twice about how build thick cell walls. I am sure there is a genetic component, but food for thought.
When I say nitrate I mean organic or synthetic. You can pour on the ammonium nitrate or blood meal to the same affect. Fast growing green ,lush, plants, with thin cell walls, and no immune system. To 99 percent of people exactly the same to the eyes, but to pests one is screaming, "eat me" and one looks like chewing through kevlar.
Stressed plants reflect light in the infrared spectrum, this is how they call in the clean up crew.