Cabbage Looper

Trichogramma egg parasitoids attack cabbage looper eggs before they hatch -- release weekly during adult moth flight. Parasitic flies (tachinids) and wasps parasitize larvae -- delay broad sprays after you notice damage to allow these beneficials to respond. Cabbage looper nuclear polyhedrosis virus (CbNPV) builds up naturally in large outbreaks -- collapsing blackened larvae are infected and beneficial to leave on plants as the virus spreads to healthy larvae. Plant dill, fennel, and sweet alyssum nearby to support parasitoid wasp populations throughout the season.

Cabbage loopers are the larvae of a mottled brown moth -- the first sign is window-pane damage where larvae eat leaf tissue from one side, leaving a thin transparent layer. This early feeding is easy to miss until holes appear. Check leaf undersides for pale green spherical eggs laid singly. Row covers installed before transplanting completely exclude egg-laying moths -- the most reliable prevention for small plantings. Light traps monitor adult moth activity and indicate when to scout intensively.

Remove crop residues promptly after harvest -- loopers pupate in plant debris and soil under host plants. Time brassica successions to avoid peak moth flight periods if you can track them locally. Interplant with dill, fennel, and aromatic herbs to support parasitoid wasps and confuse moth navigation. Cabbage loopers do not overwinter in cold climates -- they migrate north from warmer areas each season, meaning pressure varies dramatically by year.

Floating row covers over seedlings and transplants exclude adult moths from laying eggs -- remove at heading for air circulation or leave on throughout if pollination is not needed. Hand-pick larvae at night when they are actively feeding. Check leaf axils and the dense inner leaves of heading brassicas where larvae hide during the day.

Bt kurstaki or aizawai applied when larvae are under half-inch is the most effective and targeted spray -- it kills caterpillars that eat treated foliage and nothing else. Apply in the evening coating leaf axils and undersides thoroughly. Reapply every 5-7 days during peak pressure. Spinosad provides stronger knockdown on larger larvae -- apply at dusk to minimize bee exposure. Neem oil deters egg-laying and disrupts larval molting.