Swiss chard is relatively free of pests. Leaf miners are occasionally a problem. Prevent damage by covering young plants with a floating row cover in spring when leaf miner flies are most active. If these insects do damage plants, it affects only appearance, not yield. Two fungal diseases sometimes occur.
Fusarium wilt causes seedlings to wilt and shrivel and older plants to wilt and turn yellow.
Neither of these is normally a serious problem. Rotating crops, improving drainage, and maintaining good moisture and fertility levels are usually enough to keep these diseases at bay. Harvest tips Swiss chard requires only 45 to 55 days to mature, but you can harvest the baby leaves anytime. Either cut entire young plants just above the soil for salad greens, or cut off tender leaves once they reach the size you prefer. Use broader leaves in recipes that call for mature stalks, whole young leaves for salads.