This looks like leafminer damage. It's of more concern if damage appears in vegetables harvested for edible foliage, such as spinach or chard. Leafminer larvae feed inside of leaves or soft stems. So, the primary control is removing and destroying the damaged leaves. The use of row cover over plants helps prevent egg-laying in the spring. Remove alternate weedy hosts such as chickweed, pigweed, nightshade, lambs quarters, and plantain. Deep plowing in early spring to destroy infested weeds and plant material from the previous season can reduce the severity of leafminer outbreaks. Parasitic wasps are known to be effective biological control agents for leafminers. Because leafminers are protected within the plant, foliar insecticidal control is often difficult.