Aphids: Control aphids with a hard spray of water, Hot Pepper Wax, Insecticidal Soap, or Rotenone. Also, select varieties that mature later in the season when aphid populations decline.
Cabbage worms, loopers, and root maggots: The first sign of cabbage worms will be white diamond-back moths fluttering near the plants. They lay eggs in the soil, which hatch into worms that can cause severe root and head damage. To control light infestations, spray plants with Bacillus thuringiensis (BT). For heavy infestations, bait cabbage worms by mixing wheat bran into a BT solution. Add 1 tablespoon of molasses. Broadcast the bran mixture around the base of plants. Reapply as necessary. Using Reemay or Grow Guard 20, can also provide control.
Flea beetles: Flea beetles chew tiny pinholes in leaves. Early control is essential to minimize the damage. Spray young plants with Rotenone or Rotenone-Pyrethrin every 2 days. Using floating row covers such as Summer Insect Barrier can also provide control.
Symphylans: In some areas of the US, symphylans (also known as garden centipede) can severely retard the plant growth of cole crops. Only 1/4 inch long, white, and very active, they eat the root hairs of developing plants. Contact your local county extension agent if you suspect you have a problem.