_Screens and covers._

There are various ways of keeping insects away from plants. One of the best is to cover the plants with fine mosquito-netting or to grow them in hand-frames, or to use a wire-covered box like that shown in Fig. 229. In growing plants under such covers, care must be taken that the plants are not kept too close or confined; and in cases in which the insects hibernate in the soil, these boxes, by keeping the soil warm, may cause the insects to hatch all the sooner. In most cases, however, these covers are very efficient, especially for keeping the striped bugs off young plants of melons and cucumbers.

Cut-worms may be kept away from plants by placing sheets of tin or of heavy glazed paper about the stem of the plant, as shown in Fig. 230. Climbing cut-worms are kept off young trees by the means shown in Fig. 231. Or a roll of cotton may be placed about the trunk of the tree, a string being tied on the lower edge of the roll and the upper edge of the cotton turned down like the top of a boot; the insects cannot crawl over this obstruction (p. 203).

[Illustration: Fig. 229. Wire-covered box for protecting plants from insects.]

The maggots that attack the roots of cabbages and cauliflowers may be kept from the plant by pieces of tarred paper, which are placed close about the stem upon the surface of the ground. Fig. 232 illustrates a hexagon of paper, and also shows a tool used for cutting it. This means of preventing the attacks of the cabbage maggot is described in detail by the late Professor Goff (for another method of controlling cabbage maggot see p. 201):--

[Illustration: Fig. 232 Showing how paper is cut for protecting cabbages from maggots. The Goff device.]

"The cards are cut in a hexagonal form, in order better to economize the material, and a thinner grade of tarred paper than the ordinary roofing felt is used, as it is not only cheaper, but being more flexible, the cards made from it are more readily placed about the plant without being torn. The blade of the tool, which should be made by an expert blacksmith, is formed from a band of steel, bent in the form of a half hexagon, and then taking an acute angle, reaches nearly to the center, as shown in Fig. 232. The part making the star-shaped cut is formed from a separate piece of steel, so attached to the handle as to make a close joint with the blade. The latter is beveled from the outside all round, so that by removing the part making the star-shaped cut, the edge may be ground on a grindstone. It is important that the angles in the blade be made perfect, and that its outline represents an exact half hexagon. To use the tool, place the tarred paper on the end of a section of a log or piece of timber and first cut the lower edge into notches, as indicated at _a,_ Fig. 232, using only one angle of the tool. Then commence at the left side and place the blade as indicated by the dotted lines, and strike at the end of the handle with a light mallet, and a complete card is made. Continue in this manner across the paper. The first cut of every alternate course will make an imperfect card, and the last cut in any course may be imperfect, but the other cuts will make perfect cards if the tool is correctly made, and properly used. The cards should be placed about the plants at the time of transplanting. To place the card, bend it slightly to open the slit, then slip it on to the center, the stem entering the slit, after which spread the card out flat, and press the points formed by the star-shaped cut snugly around the stem."