The flow of nutrients through a plant is brought about by a process called transpiration. At the end of that process water leaves the plant, often via orifices at the edge of the leaves. This is usually as water vapor, but sometimes as water droplets, or in this case it is evidenced as a frosty fringe around the leaves' edges. This occurrance of water at those edges is called guttation. Why would a beekeeper care? Bees are known to collect these droplets as part of their water foraging. There is evidence that some systemic insecticides occur at toxic levels in those water droplets. So, even if bees don't collect nectar or pollen from these plants, they may still pose a danger to honey bees.