The Bad News Butterfly

Summer is here along with colorful butterflies including those cute white ones with a black spot on the wings. The white butterflies have a downside. They deposit eggs on your cabbage, broccoli and other cruciferous plants that will hatch in 4 to 8 days to become the dreaded green cabbage worms that munch your plants and leave behind large amounts of brownish-green excrement called frass. After munching for up to 14 days they pupate and repeat the process.

There are several strategies for addressing cabbage worms. Nature provides a natural way. Yellow jackets love to eat the worms. If you are not into yellow jackets, Bacillus Thuringiensis (BT) is a bacterial pathogen that is used for biological control over larvae. BT needs to be reapplied every 1 to 2 weeks for control. It is widely used by organic growers.

We have had good success with floating row covers over plants in the cabbage family. If you can keep the moths from laying eggs you will get no damaging worms. The plant can grow under the row cover until harvest.

If the number of worms appears manageable, you can handpick the worms and eggs. Sticky traps will catch the adult butterflies, but, will also catch beneficial insects. Interplant thyme among your cabbages as a deterrent. The worms are repelled by thyme. They are also attracted to mustard plants which can be used to draw the little critters away from your cruciferous plants. Once they take over the mustard plant, destroy it.

When all else fails, try planting red varieties of cabbage. The green worms won’t be able to camouflage, so they may stay away.