A little stumped with this one. Some of my plants are having an issue with leaves drying out, curling up, and basically disintegrating. It's only on lower leaves and seams to be pretty erratic, not all plants have it. There is no yellowing or browning, just a very slight color change to a dull shade of green. My first thought was bugs of some kind, but I can't find anything out of the ordinary. Plants are in raised beds, soil is compost/manure/little bit of sand, mulched with dry grass. Zone 8, Seattle. Thoughts?