A. The moldboard plow, which covers residues completely, is effective in several ways. It buries material that would harbor overwintering insects. It may turn up overwintering forms of insects that have burrowed into the soil and expose them to weather and natural enemies. It may bury eggs s or pupae so deeply that the young insects or larvae cannot emerge. Plowing is a recommended means of control against pink bollworm, boll weevil, corn ear-worm, European corn borer, corn root aphid, hessian fly, wheat jointworm, grasshoppers in the cultivated fields, wheat stem sawfly, and others.

B. We list six implements that partly incorporate crop residues in the soil. They are used primarily to prepare the seedbed and control weeds, but they may be effective in exposing eggs of certain insects to drying or to birds.

The one-way or vertical disk plow kills weeds. If the plowing is shallow it may expose some eggs of insects, such as grasshoppers and, crickets, in cultivated fields.

The spring-tooth harrow sometimes is used to cultivate alfalfa in the fall and expose eggs of insects like grasshoppers and crickets. But the damage to the alfalfa may be greater than the protection afforded by reduction in insect population.

Field cultivators are used to kill weeds and maintain a surface resistant to erosion. They usually disturb the soil to about the same depth as the spring-tooth harrow.

The disk harrow has an action comparable to that of a vertical disk plow run shallow, but it is not so effective in killing weeds.

The lister is not well adapted to insect control. It does not stir all the soil and does not cover all the residues deeply. Practically all the crop residue is covered in the initial operation, but some of it may be exposed again by later tillage with other implements.

The harrow is used chiefly to kill small weeds or prepare a seedbed on land previously worked with other implements.

The six implements are of use in the control of insects that feed on weeds and volunteer growth to the extent that they destroy or prevent such growth. Some of the insects for which clean cultivation is recommended as a control are pale western cutworm, wheat straw-worm, and certain wireworms.

C. Five implements leave all residues on the surface. They may be of use against insects by controlling weeds and exposing insect eggs, but in most areas that is more than offset by the protection given to overwintering insects. Their use is dictated primarily by the need to control erosion. Among the insects favored by the retention of residues on the surface are the bollworm and the hessian fly. Spider mites and carrot beetle larvae have damaged wheat on straw-mulched land under conditions where there was no injury on land without residues.

The Noble blade is used chiefly for summer fallow tillage. It is an effective weed killer under dry conditions and helps control such insects as the pale western cutworm.

The rod weeder is good for clean tillage for fallow. It makes weed-free land for the control of pale western cutworm.

Sweep implements, with sweeps wider than those of the duckfoot, are used principally to leave residues on the surface for erosion control. They are effective in killing weeds in dry areas. Sometimes wireworms are more destructive to corn when a small-grain stubble mulch had been left on the surface.

The chisel is used for loosening the soil deeply to permit penetration of water, but is of little benefit against insects.

A plow without a moldboard has the same purpose and general effect as the chisel.

ROTATION of crops often helps reduce crop injury, particularly by the insects of restricted food habits. White grubs, the larvae of June beetles, feed on roots of crops of the grass family and injure forage grasses and grain crops planted on land that has been in sod. But legume crops are unfavorable to their development. The proper use of legumes in the rotation or in combination with grasses in pastures greatly reduces white grub injuries. The corn rootworm often becomes abundant in fields that are planted to corn for two or three consecutive years. The insect is restricted in food-plant habits, however, and can be eliminated as a serious factor by suitable crop rotations.

EARLY HARVEST of some crops may prevent losses. It is effective against the alfalfa weevil in the Rocky Mountain and Pacific Coast States. In Arizona it helps control lygus bugs when it is combined with a community-wide program of clean mowing or pasturing in the winter and regulation of irrigation during the growing season. Early harvesting of wheat in Montana and North Dakota salvages a large part of the grain that otherwise would be lost when the stems infested by the wheat stem sawfly break over so that the harvester cannot pick up the heads. Early picking saves many ears of corn that would not be recovered by machine pickers in fields where the European corn borer causes stalks to break and ears to drop. The losses increase as picking is delayed. Early harvesting of corn in combination with suitable drying methods may become practical as a means of reducing losses from the corn borer.

All farm operations that promote the growth of crops; good preparation of seedbeds, use of good seed, proper fertilization, regulation of moisture in irrigation, and planting the best-adapted and most vigorous varieties are of aid in the continual competition between man and insects. Planting new crops at some distance from where they were grown the previous year or out of line with prevailing winds coming from sources of insect infestation aids against some insects. Sufficient separation between fields of small grain and corn retards the movement of chinch bugs from one crop to the other.

CERTAIN PRACTICES can be utilized to advantage in protecting timber from insect attack. Overmature timber is difficult to protect; shorter rotations would cut losses in mature timber.

Losses by a spruce bark beetle in Vermont have been avoided by cutting overmature stands of spruce. Vigorous second-growth stands can resist insects better than overmature stands. The mortality due to spruce budworm in spruce and fir stands in New England, the Lake States, and nearby Provinces of Canada is reduced if the trees are in vigorous growth at the time of defoliation. Serious defoliation of hardwood forests in New England by the gypsy moth is limited to areas having a high percentage of certain favored species. Management of the forest to hold the favored hosts to a minimum will prevent damage by the insect. Mixed stands of white pine and hardwood are rarely badly infested by the white-pine weevil, but adjacent pure pine stands are often so heavily attacked that their future value for clear lumber is destroyed. Management practices favoring the increase of hardwood species will aid in preventing losses due to the weevil. Opening of stand through logging favors the subsequent attack on certain trees by such insects as the bronze birch borer in birch, the hemlock borer in hemlock, and bark beetles in pine, which can be prevented by less drastic thinning or removal of the entire stand. Selection of better sites and proper management of tree spacing in new plantations also have great possibilities in protecting our timberlands from insect attack.

W. A. BAKER is in charge of the division of cereal and forage insect investigations in the Bureau of Entomology and Plant Quarantine. For many years he investigated insects and their control in the field, particularly cereal and forage insects in the Southwest and the European corn borer and its parasites in New England and the Midwest.