The cabbage-worm can readily be eradicated by using the arsenical poisons (156. Spraying for Codling-moth), and extensive growers of cabbage use them without hesitation before the plants begin to head. But amateurs usually prefer to use less dangerous remedies. The most desirable and successful plan adopted by the writer has been to sprinkle the plants before heading with water that has stood over gas-tar in open exposure to the sun. This seems to act as a repellent, as the butterflies very rarely deposit eggs on the leaves scented with tar. If the worms are found in the heads, they can be killed by dusting with flour just at nightfall. This kills by closing the pores of the slimy worms.
The cabbage-plusia also develops worms from eggs deposited by a winged moth. The tar-water is a repellent also of this moth, and the flour mixed with one sixth its weight of pyrethrum powder will kill the worms if any are hatched from deposited eggs.
As stated, the cutworm is mostly destroyed by fall plowing. Yet enough may be left to cut off valuable transplanted plants. The writer's plan has been to wrap the crown of every plant set out with horse-radish leaves. If a plant is cut above the leaf, it is readily observed and a hunt is made for the culprit. In most cases the plant will start from the wrapped portion when cut so high.
These brief notes on the common insects of the garden are only suggestive. The amateur desiring minute insect descriptions and habits of insects of the garden should consult some one of the works on economic entomology.