Common Swiss Chard pests

Spinach and beet leafminers (Pegomya flies) are the signature pest of chard: the adults lay small white eggs in neat rows on the undersides of leaves, and the larvae tunnel between the leaf surfaces to make tan, blistered, winding mines. Aphids, especially green peach and bean aphids, cluster on leaf undersides and growing tips, leaving sticky honeydew and sometimes spreading viruses. Flea beetles chew tiny round shot holes in young leaves, while caterpillars such as beet armyworm and cabbage loopers, along with slugs and snails, rasp ragged holes and leave slime trails in wet weather. Deer, rabbits, and groundhogs will also browse the tender leaves down to stubs.

Common diseases

Cercospora leaf spot (Cercospora beticola) is the most common disease, showing as small round tan to gray spots with distinct reddish-purple or dark brown borders that can merge and brown out whole leaves in warm, humid weather. Downy mildew appears as pale yellow patches on the upper leaf with a grayish-purple fuzzy growth on the underside. Beet curly top virus, spread by the beet leafhopper mainly in the arid West, causes stunting, inward leaf curling, and thickened, crinkled veins. Seedlings can also be lost to damping-off (Pythium and Rhizoctonia), which topples them at the soil line.

Prevention

Rotate chard, beets, and spinach so this crop family is not grown in the same bed for two to three years, and clear out crop debris and volunteer plants that harbor leafminers and leaf spot. Space and thin plants for good airflow, water at the base with drip or a soaking wand rather than overhead, and water in the morning so leaves dry quickly. Buy clean seed and healthy transplants, remove badly infested lower leaves promptly, and time plantings for the cooler ends of the season when leafminer and leaf spot pressure is lower.

Organic control

The most effective leafminer control is a floating row cover installed at planting to keep the egg-laying flies off, combined with crushing the visible white egg rows and picking off mined leaves before larvae mature. Hand-pick caterpillars, and use Bt (Bacillus thuringiensis) on young larvae when you see chewing damage. Knock aphids off with a strong water spray and treat persistent colonies with insecticidal soap or neem oil, spraying leaf undersides and encouraging lady beetles, lacewings, and parasitic wasps. Set out beer traps or copper barriers and handpick for slugs and snails, and use a copper-based fungicide only if Cercospora leaf spot is spreading. Always read and follow the product label for any spray you use.

Scouting & monitoring

Check the undersides of leaves once or twice a week starting soon after seedlings emerge, looking for the leafminer's white egg rows and early pale mines, plus aphid clusters and honeydew. Scan upper leaf surfaces for the small dark-bordered spots of Cercospora, especially during warm, humid spells, and watch young leaves for flea beetle shot holes. In hot, dry regions, watch for curled, stunted plants that signal curly top virus and its leafhopper carrier. Catching egg rows and the first few spotted leaves early lets you remove them by hand before problems spread.

Tips

Row covers plus routine scouting for leafminer egg rows on the leaf undersides prevent most of the damage this crop suffers. Harvest outer leaves regularly and cut away any spotted or mined foliage, since removing problem leaves early keeps both pests and leaf spot from building up.

General home-garden IPM guidance, focused on prevention and least-toxic control. Always read and follow the product label for any pesticide, including organic products. Page updated Aug 4, 2026.