Fairy Rings?

No, death circles -- for slugs, that is. Something has been eating the emerging bean plants, and I strongly suspect it's the slugs. I laid down do-not-cross rings of D.E. -- diatomaceous earth. 

Diatomaceous earth consists of fossilized remains of diatoms, a type of hard-shelled algae. It is used as a filtration aid, mild abrasive in products including metal polishes and toothpaste, mechanical insecticide, absorbent for liquids, matting agent for coatings, reinforcing filler in plastics and rubber, anti-block in plastic films, porous support for chemical catalysts, cat litter, activator in blood clotting studies, a stabilizing component of dynamite, and a thermal insulator. -- Wikipedia.

P.S.
D.E is white -- the blue is powdered chalk. I used an old marking chalk container to spread the D.E.