CHAPTER IX

INSECTS INJURIOUS TO CABBAGE AND OTHER CRUCIFEROUS CROPS

CABBAGE is peculiarly susceptible to insect attack, and there are probably more species of insects that injure it than any other truck crop. Other edible cole plants are attacked by the same species of insects, but as a rule suffer rather less injury. Attack begins from the time the seeds commence to sprout and continues in the case of cabbage until the edible product is ready for cooking.

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Fig. 83.-Cabbage root-maggot. a Lava; b, puparium, dorsal view; c, female fly; d, head of male; e, antenna All enlarged.

After Riley, U. S. Dept. Agr.)

KOOT-MAGGOTS

The Cabbage Maggot (Pegomya brassica Bouché).—The roots of cabbage and related cruciferous crop plants frequently suffer severe injury from the attack of the cabbage maggot (fig. 83). Young plants are most seriously affected, the mag

gots eroding the outer surface and boring into the interior of the roots, devouring the tender rootlets and frequently penetrating into the lower portion of the stalk. This insect, known also as radish maggot, is an imported pest. It does serious injury throughout the northern tier of States and Canada, attacking all forms of crucifers. It is the cause of more or less

loss to these crops each year. Since 1902 it has not only been exceedingly destructive, but has increased in injuriousness from year to year. Frequently entire crops over considerable areas are completely destroyed. Two or three generations of this maggot are indicated where it has been observed.

REMEDIES

The remedies prescribed for the seed-corn maggot are applicable. In addition there are certain preventive and other measures for its destruction that have been found successful, their use being justified by the great value of cabbage plants.

Carbolic-acid emulsion, prepared as prescribed on page 37, and diluted about 35 times, is applicable when this maggot occurs on radish.

Hand-picking, although laborious, has the merit of effectiveness, and is useful on cabbage, although not practicable on radish and similar crops. It consists in pulling up the young plants, examining the roots for eggs and maggots, and either destroying the eggs and maggots by crushing with the hand or by washing the roots in a strong solution of soap and then replanting. In most cases the plants show no ill effects from this treatment after two or three weeks have elapsed.

Methods of cultivation.-Comparatively little can be expected from various farming methods which are safeguards against other insects. Keeping the soil well hilled around the cabbage plants develops more roots, thus affording more food for the maggots and leaving enough roots to strengthen the plant itself. Crop rotation should be followed with any plants other than

crucifers or onions. With these latter it is inadvisable, as the same atmospheric or other conditions which induce injury by the cabbage maggot seem to operate in increasing the numbers of the onion pest, which has a similar distribution. Fall plowing is advisable and cabbage stumps should be removed and destroyed, especially early in the season.

Bisulphid of carbon treatment.-In case tarred paper cards, which will next be described, or other preventive methods are not employed, bisulphid of carbon may be used. It should be

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Fig. 84.-Bisulphid of carbon injector

in use

Fig. 85.-Tarred paper card in outline. One-half size. (After Goff.)

applied below the root system with a special injector or syringe,' taking care that the application is not made directly to the plants, as it is likely to kill them. A hole is made a little distance (3 or 4 inches) from the plant, and the injector inserted at an angle, as shown in figure 84. After injecting the liquid the instrument should be withdrawn and the hole closed by packing with the foot. From a teaspoonful to a tablespoonful to each young plant, and a single application, is generally sufficient.

Tarred paper cards.—The use of disks or pads of tarred paper 1 The McGowen injector, no longer for sale, has proved very successful.

for the protection of cabbage against the oviposition of the fly was perfected in 1889 by Mr. W. H. Goff.

The cards are cut in hexagonal form (fig. 85), in order to economize material, and a thin grade of tarred paper is used, as the cards made from it are more readily placed about the plant without being torn. The blade of the tool, which can be made by a 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 figure 86. 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 around, 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 perfect, and that its outline represent an exact half hexagon.

cutting cards. About one-fourth

To use the tool, place the tarred paper on the Fig. 86.-Tool for end of a section of wood and first cut the lower edge into notches, as indicated in figure 87, using size. (After Goff.) only one angle of the tool. 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

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Fig. 87.-Showing how tool is used. dotted line indicating position
of edge of tool. (After Goff)

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 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.

A Wisconsin grower protected 7,000 plants and secured a splendid crop, while unprotected plants nearby would have been a complete failure if the maggots had not been picked off by hand. Others have reported similar success. One lost only 25 plants out of 10,000 to 15,000 that he protected with the cards, where ordinarily he would have lost from 75 to 90 per cent. of the crop.

The tarred cards are applicable to cabbage and cauliflower only, but it is claimed by those who have employed them that they are cheaper, more practicable, and more efficient than anything as yet devised for preventing the ravages of the cabbage maggot. Success in using them is dependent upon their being properly applied, to fit tightly, so that the fly is unable to obtain access to the stem for the deposition of her eggs. Cards must be renewed and their use continued for each maggot year to be effective.

Coverings and hellebore.-Some success has also been attained by covering young plants in seed-beds with netting and by applying hellebore about the roots.

The Seed-corn Maggot (Pegomya fusciceps Zett.).—This species, previously considered on page 106 on bean and pea insects has been identified with attack to cabbage, turnip and radish on numerous occasions and in many localities. When occurring on such plants it should be treated in about the same method as the cabbage maggot.