Planning reference

Slugs vs Cabbage Worms

Separate slug slime trails and ragged night chewing from cabbage worm eggs, frass, white butterflies, and brassica head contamination risk before changing water, mulch, row covers, Bt timing, or harvest decisions.

What each brassica leaf signal means

Slugs
Slugs are soft-bodied mollusks that rasp irregular holes in leaves, seedlings, stems, and tender growth. They feed mostly at night or early morning, favor cool moist shelter, and often leave shiny slime trails near the damage.
Cabbage worms
Cabbage worms on brassicas usually means imported cabbageworms, cabbage loopers, diamondback moth larvae, or related caterpillars chewing cabbage-family leaves, buds, and heads after butterflies or moths lay eggs.
Slime trails and ragged night chewing
Shiny slime, ragged irregular holes, shredded leaf edges, damage that expands after wet nights, and pests hiding under boards, mulch, weeds, or plant debris point toward slugs before assuming caterpillars.
White butterflies, green caterpillars, and frass
White cabbage butterflies, single underside eggs, velvety green larvae, looping movement, enlarged brassica holes, dark green frass, and feeding in cabbage or broccoli heads point toward cabbage worms and loopers.
Moist hiding places, undersides, and row-cover timing
Slug decisions hinge on wet shelter, mulch, debris, morning or drip watering, and night scouting. Cabbage worm decisions hinge on flipping brassica leaves, head contamination risk, row covers before egg-laying, and Bt timing while larvae are small.

Brassica leaf scouting workflow

Separate the scouting window first
Do not treat every ragged brassica hole as the same pest problem; scout at night or early morning for slugs, slime trails, cool moist hiding places, mulch, debris, and irregular chewing, then flip brassica leaves for white butterflies, underside eggs, velvety green caterpillars, frass, enlarged holes, head contamination risk, row-cover timing, and Bt timing before drying beds, changing irrigation, covering rows, spraying, or harvesting heads.
Check slime and shelter before spraying
Look under mulch, boards, leaf litter, dense weeds, and lower leaves after damp nights. Slug pressure rises when sheltered soil stays cool and moist, so habitat and watering changes come before treating a brassica caterpillar problem.
Flip brassica leaves and inspect heads
For cabbage worms, inspect leaf undersides, midribs, growing tips, and forming heads for eggs, green larvae, looping larvae, frass, and chewing that enlarges between veins. Head crops need earlier decisions than older outer-leaf damage.
Time covers before pests are inside
Row covers help when they exclude cabbage butterflies before eggs are laid. They do not fix slug shelter under wet mulch, and late covers can trap pests underneath if plants are already infested.
Match Bt and moisture decisions to the confirmed pest
Bt is most useful on small exposed caterpillars, not slugs. Morning drip or root-zone watering can reduce slug-favorable leaf wetness without stressing brassica seedlings or hiding a cabbage worm outbreak.

Use these paths

Source basis