The Next Garden Plague: Cabbage Loopers

By Charles Cheyney, University of Idaho Extension Educator

In this county ,it doesn’t seem to matter too much what you want to grow, there always seems to be a pestiferous or climatologically reason that makes it hard to work out well! Two weeks ago, the early-instar grasshoppers started moving into fields, yards and gardens from the desert and waste areas. This week it looks like the cabbage loopers are moving in to work over one of the easier to grow and store vegetables in our area.


Cabbage loopers are one of a family of Lepidoptera pests that attack cole crops. They may damage young plants and eat ragged holes in the leaves of older plants. In the early stages of plant growth they are usually controlled by a variety of natural enemies and disease, but as cabbages begin to head, and the loopers bore into the heads they are protected from their enemies and from insecticide management.

Damage by cabbage loopers to heading cabbage includes boring holes though the heads and contaminating the heads with their bodies and frass. Most of us don’t want to be surprised with this in our coleslaw!

At commercial scale, monitoring programs and release of parasites may be successful. At the garden level these practices are more problematic. Gardeners probably need to depend on two strategies. One is exclusion. This would be installing and maintaining floating row covers before the plants are infested with loopers, preventing the adults from laying eggs. The second is insecticide.

The insecticide strategy has two options: One is non-organic material, and two, the better choice is the use of bacillus thuringiensis (bt). If you follow the non-organic insecticide path be sure to read and follow instructions (for everything you put in the tank)and observe the harvest interval.

Bacillus thuringiensis a naturally occurring toxin produced by a bacterium, which is a stomach poison for many caterpillar pests (including horn worms and corn ear worms). It is marketed for gardens under a number of trade names including “bT”, “Thuricide” and “Dipel”. This material stops caterpillars from feeding and they starve to death. This means application to early instars is important, (since the more you eat the bigger you get), and in the case of our cabbage, we need the larva to stop feeding BEFORE they bore into the head where they are protected from everything. I suggest that gardeners who are experiencing holes in their cabbage leaves begin periodic (5-7 day) application of bT insecticide while the heads are forming. Bt can be applied up to the day of harvest.

If you would like more information about integrated pest management of cabbage loopers go to UC-IPM at:

http://www.ipm.ucdavis.edu/PMG/r108301011.html

or

PNW Insect Management Handbook at:

http://uspest.org/pnw/insects?22VGTB13.dat