Hello Rochelle,

The damage pictured is caused by leafminers, which are insect larvae that are feeding in between the upper and lower leaf layers, chewing out the tissues and leaving the thin membrane of the leaf surfaces behind as they go, which sometimes dries out and shrivels or changes color (pale, or dark as the tissues die). When extensive, it can resemble fungal infections or other damage. These are very common nuisance pests of vegetables and other plants (each species of leafminer tends to be particular about what host plants it can use), and beets and chard are among the usual victims.

Management tips for existing infestations and prevention tips for the future are included in the page linked above. Plants as young as these chard might not be able to regrow well when damage is affecting most of their leaves, but you can see how they fare if you don't want to replace them yet. Snip off any heavily-mined leaves and see if the plants grow replacement foliage. If you haven't fertilized recently, a dose of general-purpose fertilizer may help speed that up. (Liquid fertilizers take effect more quickly, but don't last as long; granular fertilizer pellets are time-release and take a while to have an impact but last for a longer period of time.)

Stagnating growth may be just due to the tissue loss from the leafminers, since it reduces the plant's ability to photosynthesize to make the carbohydrates it needs to grow. Otherwise, insufficient nutrients in the soil might be a contributing factor, but it's hard to guess, and over-fertilization poses its own problems. Depending on whether these are in the ground or in a container, the pages below might be helpful with guidance about fertilization:

• Maintaining Container Grown Vegetables
• Fertilizing Vegetables

Our other vegetable pages may also be useful, if you haven't encountered them already, for general plant care and other information.

Miri