ARTIFICIAL METHODS OF CONTROL 39 



Healthy Crops. In the majority of cases a vigorous, thoroughly 

 healthy plant is not only better able to withstand insect injury but is 

 also less liable to attack than one enfeebled or not thriving for any reason. 

 Thorough cultivation, the use of fertilizers and the removal or repair of 

 injured or diseased parts or plants as soon as these appear, will aid 

 greatly in insuring the desired results. 



Clean culture is also an important factor. Weeds not only interfere 

 with successful crop growth but may in some cases at least, consume 

 plant food in the soil which might otherwise be utilized by the crop, 

 thus reducing its vigor, and in addition they provide wintering places 

 for many insects. Rubbish left on a field after the harvest often serves 

 the same purpose: insects frequently find protection during the winter 

 in tall grass too often left surrounding the trunks of fruit trees, and 

 many serious pests winter close to the ground in grass fields. Decaying 

 fruits and vegetables harbor insects and should be composted. Weeds 

 should therefore be killed and burned and the grass kept down in or- 

 chards. Burning over grass fields in early spring in the Northern states at 

 least, choosing a time when the dead growth is dry enough to burn while 

 the living parts of the grass are still so wet as to be uninjured by the heat 

 is often a valuable way in which to destroy many pests which winter 

 there. Clean culture in all its forms, not forgetting fence-line and road- 

 side growth will do much to reduce loss by insects. 



Crop Rotation. The rotation of crops often has an important bearing 

 on insect control. Any crop attacked by a particular species of insect 

 should not be followed by another, either of the same kind or by a differ- 

 ent one which is also fed upon by that species of insect. How far this 

 principle can be carried out in practice, however, is a different matter. 

 To break up sod land and plant corn for the first crop is merely to follow a 

 mixture of grasses with a single kind of a grass and from the standpoint of 

 insect control at least, is unwise. It is the usual practice though, and 

 how far it would be wise to depart from it, planting beans, buckwheat or 

 perhaps potatoes instead, is a question, though these last-named crops 

 would be much more likely to be free from insects. The entire subject 

 of crop rotations which are satisfactory from the standpoint of agri- 

 culture and are also correct when insect problems are considered, is still 

 in a far from settled condition, and needs prolonged investigation. 



Plowing. Many serious pests winter in the ground. Fall plowing 

 after they have formed the cells' in which they pupate or winter, as the 

 case may be, will break many of these and remove the protection they 

 give : eggs laid in the ground will often be buried so deeply that the larvae 

 if they hatch in spring will be unable to reach the surface. Similarly, 

 thorough cultivation in the summer, where it is possible, besides being 

 good for the crop, has an injurious effect on insects there. 



In some cases early fall plowing gives the best results : in others, late 



