Water Drops Do Not Burn Foliage
I have been asked many times if it is true that water drops on plant leaves can lead to burning of the leaf tissue in strong sunshine.
It is true that a water drop can act as a lens…… but in order for the sunlight to be focused on the surface of the foliage, the drop must be a perfect, rounded semi-circle. In common experience, you know that water droplets are flattened. Physicists know that the focal point of such a lens (if a focal point exists) is either above or below the leaf surface, not on it. Since light is never focused on the leaf cells, its diffuse energy is never enough to heat the cells to the point of damage.
Another way to think of this is to consider that if the light DID focus on the leaf surface beneath the drop, the heat would cause the droplet to quickly evaporate……. before the cells could be damaged.
Water damage CAN occur when the drop is dramatically colder or hotter than a leaf surface but the explanation that “the drops act as a magnifying glass and burn the leaf” should be relegated to the folk tale bin.