Cabbage, Napa

Rapid foliar blight reduces plant vigor and yield; severe infections can kill leaves while stems and fruit often remain initially intact.

Favored By

Cool to moderate temperatures, prolonged leaf wetness, high humidity, cloudy weather, dense foliage, and windborne spores.

What It Looks Like

Angular yellow or pale-green spots on upper leaf surfaces with gray, purple, or dark downy growth beneath, most visible on humid mornings.

Prevention

Plant resistant cultivars where available; improve airflow; use drip irrigation; avoid overhead watering late in the day; remove volunteer hosts.

Management

Remove infected leaves or plants when practical; monitor regional forecasts for cucurbit downy mildew; use a crop-labeled preventive fungicide when local risk is high.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Seeds rot before emergence or young seedlings collapse, producing thin stands and sudden losses in flats or garden rows.

Favored By

Cold or waterlogged soil, contaminated mix or containers, poor drainage, deep sowing, dense seedlings, low light, and overwatering.

What It Looks Like

Pre-emergence seeds become soft and brown; emerged seedlings develop a water-soaked or pinched stem at the soil line and topple.

Prevention

Use sterile seed-starting mix and clean containers; sow at the proper depth; provide warmth, drainage, light, and airflow; avoid crowding and overwatering.

Management

Discard affected seedlings and nearby mix; reduce watering; improve light and airflow. Fungicides have limited value after collapse and must be specifically labeled.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Stem and crown infections cause watery rot, wilting, lodging, and plant death in beans, lettuce, tomatoes, cucurbits, and many other crops.

Favored By

Cool moist weather, dense canopies, prolonged leaf wetness, poor airflow, flowering plants, and soils containing long-lived sclerotia.

What It Looks Like

Water-soaked lesions become bleached and covered with cottony white growth; hard irregular black sclerotia form inside or on stems.

Prevention

Rotate to grasses or other nonhosts; space and stake plants; use drip irrigation; control broadleaf weeds; remove infected plants before sclerotia mature.

Management

Pull and discard infected plants and nearby debris; reduce canopy moisture; avoid cultivating contaminated soil into new beds; fungicides are preventive, not curative.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Enlarged roots cannot take up water and nutrients efficiently, causing stunting, daytime wilt, poor head formation, and plant death.

Favored By

Acidic, cool moist soil; contaminated transplants, tools, and soil; poor drainage; and repeated cabbage-family crops.

What It Looks Like

Roots form distorted spindle-shaped or club-like swellings; aboveground plants are stunted, yellow, and wilt during warm parts of the day.

Prevention

Use clean transplants; raise soil pH according to a soil test; improve drainage; rotate at least 4–7 years; control crucifer weeds; clean tools.

Management

Remove infected roots without spreading soil; no cure exists. Avoid moving soil from affected beds and grow nonhosts or resistant cultivars.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Leaf and head lesions reduce photosynthesis and quality; spots on broccoli and cauliflower heads make produce unmarketable.

Favored By

Warm humid weather, extended leaf wetness, infected seed or residue, splashing water, and continuous brassica crops.

What It Looks Like

Round brown to black spots with concentric target rings and yellow halos; dark lesions may develop on heads, pods, and stems.

Prevention

Use tested seed and resistant cultivars; rotate; remove residue and crucifer weeds; space plants; use drip irrigation.

Management

Remove infected leaves and debris; avoid handling wet plants; use a labeled protectant fungicide where disease is recurrent and conditions remain favorable.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

A systemic bacterial disease causes progressive leaf blight, vascular blackening, stunting, and poor heads in cabbage-family crops.

Favored By

Warm wet weather, infected seed or transplants, splashing rain, overhead irrigation, crucifer weeds, and handling wet plants.

What It Looks Like

Yellow V-shaped lesions advance inward from leaf margins; veins within lesions turn black and stem vascular tissue may darken.

Prevention

Buy certified seed and healthy transplants; rotate 3–4 years; remove crucifer weeds and residue; use drip irrigation; avoid working wet plants.

Management

Remove infected plants promptly; sanitize tools; copper products may slow spread but do not cure systemic infection and can injure plants.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Sap-feeding colonies distort tender growth, cause yellowing and sticky honeydew, and may transmit plant viruses.

Favored By

Soft new growth, excess nitrogen, sheltered plants, and warm moderate weather.

What It Looks Like

Tiny (about 1/16–1/8 in), soft, pear-shaped insects; green, black, yellow, gray, or pink; two tailpipe-like cornicles.

Prevention

Avoid excess nitrogen; inspect leaf undersides; conserve lady beetles, lacewings, hoverflies, and parasitoid wasps; control ants that protect aphids.

Management

Knock off with water; prune badly infested tips; use insecticidal soap or horticultural oil with thorough contact coverage. Repeat only as label directs.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Adults and nymphs suck sap, yellow leaves, reduce vigor, and excrete honeydew that supports sooty mold.

Favored By

Warm protected sites, greenhouses, dense foliage, weeds, and heavily fertilized tender growth.

What It Looks Like

Adults are tiny white, mothlike insects that flutter when disturbed; nymphs are flat, oval scales on leaf undersides.

Prevention

Inspect transplants; remove infested leaves and weeds; use screens in protected growing; avoid broad-spectrum insecticides that kill natural enemies.

Management

Use yellow sticky cards for monitoring; vacuum adults on small plantings; apply insecticidal soap or horticultural oil to leaf undersides.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Adults chew numerous small shot holes in leaves; seedlings can be stunted or killed. Some larvae feed on roots.

Favored By

Warm sunny weather, young seedlings, nearby weeds or crop residue, and repeated planting of susceptible crops.

What It Looks Like

Tiny (about 1/16–1/8 in), shiny dark or striped beetles with enlarged hind legs that jump when disturbed.

Prevention

Use row cover immediately after planting; remove weeds and residues; rotate crops; plant vigorous transplants or delay planting where practical.

Management

Remove cover at flowering when pollination is needed; use labeled kaolin clay or insecticides only when feeding threatens establishment.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Velvety green larvae chew irregular holes in brassica leaves and contaminate heads with frass.

Favored By

Brassica crops through spring and fall; warm weather when white butterflies are active.

What It Looks Like

Larvae are velvety green with faint yellow stripe; adults are white butterflies with black wing tips and spots.

Prevention

Use insect netting or row cover before egg laying; remove brassica weeds and residues; inspect leaf undersides.

Management

Handpick eggs and larvae; use Bt kurstaki on small caterpillars or spinosad where labeled; direct sprays into cabbage heads.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Larvae chew ragged holes and may bore into cabbage heads; frass contaminates produce.

Favored By

Warm weather, continuous brassica plantings, and southern migrations of adult moths.

What It Looks Like

Green caterpillar with white side stripes and only two pairs of mid-abdominal prolegs; moves by looping its body.

Prevention

Use insect netting; destroy crop residues; remove crucifer weeds; scout weekly for eggs and small larvae.

Management

Handpick; apply Bt kurstaki while larvae are small or spinosad where labeled; rotate insecticide modes if repeated treatment is necessary.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Small larvae make windowpane feeding and holes in brassica leaves and heads; populations can develop insecticide resistance.

Favored By

Warm dry periods, continuous brassica production, and nearby crop residues or crucifer weeds.

What It Looks Like

Small pale-green larvae taper at both ends and wriggle or drop on silk when disturbed; adult is a slender gray-brown moth.

Prevention

Use row cover; rotate crops; remove crucifer weeds and residues; conserve parasitoid wasps; scout for small larvae.

Management

Use Bt kurstaki or spinosad on young larvae where labeled; obtain thorough coverage and avoid repeated use of one mode of action.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Larvae tunnel between leaf surfaces, creating serpentine or blotchy mines that reduce photosynthesis and market quality.

Favored By

Warm weather, susceptible leafy crops, weeds, and broad-spectrum insecticide use that kills parasitoids.

What It Looks Like

Tiny dark flies are seldom noticed; pale legless larvae live inside leaves; mines are winding trails or translucent blotches.

Prevention

Use row cover; remove host weeds; inspect transplants; remove mined leaves before larvae exit; conserve parasitoid wasps.

Management

Crush larvae within mines or remove leaves; insecticides often miss protected larvae, so target adults/young larvae only with labeled selective products.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Larvae feed on brassica roots, causing wilting, poor growth, and root tunneling, especially in seedlings.

Favored By

Cool moist spring soil, high organic matter, fresh manure, and continuous brassica crops.

What It Looks Like

Small gray adult fly; white legless maggots in or beside roots; eggs are tiny white slivers at the stem base.

Prevention

Use row cover before emergence; rotate; delay planting in high-risk areas; use transplants with firm stems; remove brassica residues and weeds.

Management

Remove badly infested plants; mound soil around stems to encourage new roots; beneficial nematodes may help under suitable conditions; preventive labeled products vary by state.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

Sap feeding causes white stipples, yellowing, wilting, and death of brassica plants when numbers are high.

Favored By

Warm weather, overwintered brassica debris, crucifer weeds, and continuous cole crops.

What It Looks Like

Shield-shaped black bug with bright red, orange, or yellow markings; barrel-shaped black-and-white eggs laid in neat clusters.

Prevention

Remove crucifer weeds and crop residue; rotate; use row cover; plant trap crops only if they will be monitored and destroyed.

Management

Handpick adults and egg clusters; remove heavily infested leaves; insecticidal soap can suppress young nymphs; use labeled products if necessary.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.

They rasp irregular holes in leaves, stems, seedlings, and low fruit and leave silvery slime trails.

Favored By

Moist shade, dense mulch, weeds, boards, stones, and frequent evening irrigation.

What It Looks Like

Soft-bodied mollusks; snails carry shells while slugs do not; active mostly at night or during wet weather.

Prevention

Water in morning; improve airflow and drainage; remove hiding places and weeds; keep mulch away from seedling stems; use barriers where practical.

Management

Handpick at night; use board traps; apply iron phosphate bait according to label and protect it from children, pets, and wildlife.

For Cabbage, Napa: Reviewed Research Library baseline; local occurrence and treatment timing vary.