Cabbage is a cool season vegetable that can grow into the warm season, but it gets progressively harder to grow. Warmer weather can cause the plant to bolt and a heavy rain can cause the head to split. Plus, there are all the insects that love to munch on cabbage.
Cabbage transplanted in February can be harvested before harmful caterpillars arrive. Cabbage planted in the fall will mature when the weather cools down and the threat from insect damage is over. Fall cabbage can even be left in the garden through the winter to get a head start in the spring. It takes a really cold freeze to damage a mature cabbage plant.
Once warmer weather settles in, the bugs arrive. Cabbage growing in May attracts a variety of caterpillars. Diamondback Moth Caterpillars are the most common cabbage pests in South Carolina. We also see the Cabbage Looper, Imported Cabbageworm, Cross-Striped Cabbageworm, Armyworms, and Cabbage Webworms.
The easiest way to avoid these pests is to grow cabbage in cooler weather. Keeping a clean garden with few weeds and removing crop residue will leave fewer places for pests to overwinter. It is also possible to hand pick the caterpillars off the cabbage, but that is something that must be done every day. Also, a fine mesh net over the plants can prevent moths from laying egging on the cabbage in the first place. Planting companion flowers near the cabbage can also help control caterpillars. Plants with small flowers like sweet alyssum, parsley, dill, cilantro, buckwheat, and fennel will attract wasps and parasitic flies which feast on caterpillars.
I do not use pesticide on cabbage. The whole plant is food, and I do not like to put poison on anything I will eat. Also, pesticide in the garden will kill beneficial insects and spiders. Killing the good bugs will only make your bad bug infestations worse in the future.