Cabbage worms are the larval form of the Cabbage White butterfly. It is useful to know what both the larva and the butterfly look like, because seeing either near your plants most likely means that you’ll start seeing damage to your brassicas (such as cabbage, broccoli, and kale.)
Butterfly: off-white wings, with one or two grayish-black spots per wing. The wingspan is roughly two inches across.
Larva (which is the form that does the actual damage): velvety green, inchworm-type caterpillar that is roughly one inch long.
Eggs: These will be found on the undersides of leaves, and are yellow and oval-shaped.
The larva build a chrysalis in the fall, and hatches as the Cabbage White butterfly in spring. The butterfly feeds on nectar, and lays single eggs on the undersides of plants of the brassicas family. The eggs hatch in five to seven days. The larva (cabbage worm) feeds voraciously on brassicas, building up energy to make its chrysalis and metamorphize over the winter.
Signs of Cabbage Worm Infestation:
Because of their voracious appetite, an “infestation” can be as few as two or three worms per plant. Look for holes being chewed from the centers of leaves in kale and cabbage, as well as entry holes chewed to the interior of heads of cabbage. In particular, look on the undersides of leaves, because this is where the cabbage worms usually hang out. They also produce dark green droppings that are fairly noticeable.
Effect on Garden Plants:
Cabbage worm can make the plant die within few days if you don’t take this matter seriously. The ability of plant to photosynthesize becomes low as cabbage worms keep eating the leaves. In case of minor infestation, the plants remain edible but they look unsightly. Before cooking the broccoli and cabbage, make sure that you wash the plant careful because cabbage worms can get to the interior of the heads.
Organic Controls for Cabbage Worms:
If you see the butterflies around your plants, you need to check your plants regularly. While checking the plants, hand-pick the worms and destroy all the them. In case, you notice a serious infestation, you should apply the bacillus thuringiensis, which is easily available from garden centers.
Floating row covers are the most important thing for preventing the infestation during the early summer and spring because cabbage worms lay eggs durig this period.
Insert every head into a nylon stocking to avoid the worms getting into them and leave the stockings on before you harvest them.
Read original article here: http://organicgardening.about.com/od/pestcontrol/p/cabbageworms.htm