Q: There are large brown blotches on the leaves of my chard. Was this caused by our unusually hot spring?
A: Those translucent blotches that look like they were scorched by the sun are caused by beet leaf miners, tiny black and yellow flies that lay their eggs on the leaves of spinach, beets and chard. The eggs hatch into pale green maggots that feed inside the leaves, resulting in hollowed-out, translucent beige blotches filled with frass (polite word for bug poop).
The insect won’t kill your plant, and you can eat any unaffected parts, but you obviously won’t want to eat any of the blotched sections of the leaves.