Cabbage looper

Cabbage loopers (Trichoplusia ni) are the fleshy, green caterpillars that can be found inside broccoli, cabbage and cauliflower heads throughout the season.  They also affect canola - a relative of plants in the cabbage family - so damage in home gardens tends to be worse in areas near canola fields.

The adult form of the cabbage looper is a small grey/brown mottled moth. The small white butterfly is often found flying around the garden.  The moths lay their yellow coloured eggs on the underside of leaves which then hatch into the caterpillars. The adult butterflies do little damage.

The caterpillars chew holes in the leaves of the plant but their green mushy excrement can be found throughout the crevices of leaves and heads.  Although the excrement is not harmful to humans, it is unsightly.

Control:

Covering plants with thin supported crop covers will prevent butterflies from laying their eggs on plants.  Bacillus thuringiensis (Bt) is a type of bacteria that is not harmful to humans and can be sprayed on the plant to control loopers. Unfortunately, it will also kill all butterfly caterpillars it comes into contact with as well, so covering your plants with insect row cover is the best prevention. Row covers are available at most garden centres.