CHAPTER II PREVENTION BY FARMING METHODS HAVING Shown in a general manner what is desirable for the best understanding of the subject under consideration, it is next in order to point out how this knowledge may be utilized in the prevention or mitigation of injury. A knowledge of the origin and distribution of insects enables us to judge of the probable and ultimate spread of introductions from abroad and from one portion of our country to another. Thus we can predict, with a considerable degree of certainty, that certain species will not be injurious beyond certain boundaries, and that others will widen their range beyond known limits. Knowing the effects of atmospheric conditions, of heat and cold, dryness and humidity upon insect reproduction, we can be forewarned of injury and can plan accordingly. Experience having taught that the clearing of uncultivated or neglected land is almost certain to be followed by depredations of insects which had inhabited the wild plants and weeds, we are enabled to plant such crops as will be least affected by these insects. Knowing what insects are controlled by predaceous, parasitic and other enemies, such as beneficial insects, contagious diseases, wild and domestic animals, we can in many cases, untilize these natural agencies in our warfare against them. Most of the different farming methods which will be considered are of use in combatting insect enemies of cereals; in short, without their employment it is impossible to avoid losses from these insects, as it is seldom practicable to use insecticides on growing grain. The usefulness of many of these methods is due to the slow spread of many species except at more or less regular periods of migration and the strong tendency which many have of depositing their eggs in the same field where they have bred or hibernated. The value of these methods in the treatment of the Hessian fly is summed up by Prof. F. M. Webster in the statement that "four-fifths of its injuries may be prevented by a better system of agriculture." SELECTION OF PLACE AND TIME FOR PLANTING With a knowledge of the insects which attain their highest development in sandy locations, in marsh land or in the neighborhood of woodland, we can prepare for attack from them after the ground has been cleared for planting. Much depends upon a judicious selection of the crop to replace weeds or to be grown in forest clearings or in land that has long laid waste. Unfortunately the crops frequently selected for planting in new land are the very ones most subject to attack, and if farmers generally are to preserve their crops from insect injury they must employ new tactics. Corn and other cereals, potatoes and strawberries are crops especially attractive to insects which have developed in unused land. They should therefore not be planted in new land until after some less susceptible plant be used as a first crop. Buckwheat and clover are less likely to be injured. Corn should not as a rule be planted in marshy tracts or in reclaimed river beds owing to the danger of injury from bill-bugs, root-worms, wireworms and the like. Nor should corn follow wild grasses, which are liable to be affected by the same classes of insects as well as cutworms and white grubs. Next in order is the choice of the proper time to plant to avoid insects which are liable to attack the crops which we intend to grow. With early and late planting must be combined occasional planting between two generations of an insect, and the timely disposal of the crop, particularly if this is damageable. Late planting is practiced against numerous insects with excellent success, the object being to have the crop appear after the disappearance or dispersion of the insect whose ravages are feared. It is, in fact, a standard remedy against some insects. THE MAINTENANCE OF VIGOROUS GROWTH If plants be weakened through atmospheric or other cause or through a combination of unfavorable conditions they are as a general rule more subject to injury by insects, but there are many crop plants, as for example certain varieties of wheat, that the ranker the growth the more they are subject to infestation by such insects as the Hessian fly. Some have claimed that weak plants only are subject to injury, and that plants might be grown by artificial methods for the production of such great vigor that insects would not seriously damage them. Although this might be possible with a limited number of plants, we can not now procure all of the most favorable conditions. As an instance, we have only to cite the reported successful use of kainit and nitrate of soda as a remedy for wireworms and some other insects in New Jersey, and their failure when applied in other states. Possibly soil and atmospheric conditions have in some instances had some bearing upon these failures. Most failures, however, are due to wrong methods. BURNING OVER FIELDS AND WASTE LANDS A farm practice in favor in many regions against cereal-feeding insects consists in burning over fields after harvest or before plowing. It affects particularly such insects as hibernate on or just below the ground. Among well-known pests that can be reached by this method are cutworms, many of which live all winter long above the earth's surface partially grown, also webworms, grasshoppers, aphides and plant-bugs, and some forms of beetles and other insects which hibernate in the adult stage at or near the surface. CROP ROTATION One of the best of farming methods is crop rotation, as it serves several purposes. If pursued on scientific principles it is not only a benefit to the land, but is one of the easiest means of preventing attack from insects, fungous and other diseases, and weeds. In a general way it may be said that crops of like kind, that is, belonging to the same botanical groups, and much subject to insect attack, should not be planted in successive years. in the same fields. Thus it is inadvisable to plant corn in old wheat fields, and it is equally unwise to grow small grains after corn. Where insects occur like the bollworm, which attacks several plants, injuring tomato fruit, corn ears, bean pods, etc., in similar manner, still greater care is necessary in selecting the land for planting. It follows that it is bad practice to plant corn after tomatoes or tomatoes after corn, or to plant either of these crops in or near cotton fields. Here is where a knowledge of botany sufficient to enable the grower to know the botanical families to which his crops, as well as the weeds, belong becomes of value; since with the exception of insects known as general feeders, most species feed by preference on one or more plants of the same botanical group. Thus an insect destructive to cabbage will attack any cole crop, such as turnip or radish, and weeds such as wild mustard and pepper-grass; hence care should be used not to plant cabbage in fields in which the other plants have grown. The same rule holds with plants of the cucumber kind. Melons should not follow squashes, nor pumpkins cucumbers. Rotation of crops is practically the only means of dealing with some of the most important insects, among which are the western corn root-worm. Where diversified farming is practiced, such leguminous plants as crimson clover and cowpea are most useful as alternates, because valuable as soil restorers, and not as a rule subject to serious insect injury. DIVERSIFIED AGRICULTURE Entire plantings are frequently failures because growers rely on single, or, at best, two or three crops for a livelihood. The practice of growing large areas to cotton in the South is an example. Occasionally this is varied by corn or tobacco, and all three crops are likely to be injured by the same insects, e. g., by the bollworm, corn-ear worm or tobacco budworm, as this one species is variously termed. In Texas there was at one time the threatened danger of an abandonment of cotton culture owing to the rapacity of the boll weevil. The large appropriations that have been made available by Congress for the control of this pest should result in materially reducing the losses occasioned by it, which now bids fair to seriously hamper the production of this staple which nets our country $500,000,000 or more annually. The melon or cotton aphis has done great damage in Texas since the beginning of the new century and various crops in the South are threatened with new pests. It is quite a problem, therefore, to decide what may be grown most advantageously. Other striking illustrations of the danger of cultivating a single crop can be pointed out. In some years in the past it was simply impossible for truckers in parts of Maryland and Virginia to make a living from cabbage, or other cruciferous crops or from melons and other cucurbits, but by growing several crops of widely different kinds they make a profit. In the Northeast the farmer does not have such problems with which to contend and yet raises many crops, keeping his hands busy nearly the year round, and there is no excuse for growers in the South and elsewhere cultivating only a few crops when by diversified or general farming losses from insects, from plant diseases, and from adverse climatic conditions could be avoided. |