The sucking insects obtain their food, not by eating the leaves, but by inserting their “beaks” into the plant tissue and sucking its juices. Since it is not feasible to poison the sap of plants to kill the insects, the best method is to spray them with what are known as “contact” insecticides. These must be applied in such a way that they actually come in contact with the insects. Soap solutions, kerosene emulsion, and nicotine are the principal contact sprays.
Sometimes, instead of using sprays it is more convenient to use dry insecticides in the form of powder. This is particularly the case when a spray-pump is unavailable or the water supply not close at hand.
No matter in what form these insecticides are applied, the operation must be done thoroughly or little benefit will result. The contact sprays should be applied with force in such a way that every insect is covered. To apply the stomach poisons a fine, mist-like spray should be used which will coat the leaves with a thin film of poison. If too much is applied there is a tendency for the mixture to run into globules, which concentrates the poison at the tip of the leaves. This may result in injury to the plants and is not effective in coating the whole of the leaves.
The feeding habits of some insects make it almost impossible to control them by spraying; so traps, poison bait, hand picking, repellents, or screening the plants to prevent access of insects are resorted to. These measures are fully described in connection with the insects against which they are used. Following are some of the more important insect pests.
Beets.—Flea-beetles (small, very active insects, as indicated by their name), blister-beetles, and various caterpillars, which eat the leaves, attack beets. Lead arsenate[[4]] should be applied as soon as the injury is noticed.
| [4] | Various spray formulas will be found at end of chapter. |
Cabbage.—Probably the worst insect pest of this crop is the cabbage-worm, a green caterpillar which hatches from eggs laid on the leaves by the common white butterflies, which may be seen flitting about the garden from early spring until fall. Spraying the plants with arsenate of lead to which a “sticker” has been added to make it adhere to the leaves is a standard remedy. Cabbage is also attacked by flea-beetles and caterpillars of various kinds, which are controlled by the same methods adopted for the cabbage-worm.
Cauliflower.—Same pests as cabbage.
Corn.—The corn earworm is one of the worst of the pests attacking corn. This is a caterpillar which at first feeds on the “silk” and later penetrates the ear and eats the kernels. It is very difficult to control this insect. Lead arsenate sprayed or dusted on the silk as soon as it appears is a partial remedy.