ARTIFICIAL METHODS OF CONTROL 41 



least exposing the plant treated, to the risk of greater injury than that 

 caused by the insects. 



Heat. — Heat can sometimes be used to advantage for the destruction 

 of insects. A temperature of 125°r. is enough, if maintained for 3 or 

 4 hr., to kill insects infesting grain, seeds, etc., and also almost all house- 

 hold pests at least. Where heat can be applied in this way, therefore, it 

 is a special method of control of considerable value. 



Miscellaneous Methods. — Borers in trees present particular difficul- 

 ties, being so hard to reach, and cutting them out by hand is frsquently the 

 best control method. Protective coverings over or around plants may 

 sometimes be used to advantage, as for example, netting over young 

 cucumber and squash plants. Sticky bands placed around the trunks of 

 trees keep insects which cannot fly from crawling up to the leaves. 

 Pieces of bark or boards on the ground near plants, under which insects 

 may crawl for protection at night, as some do, are good traps for such 

 insects, if these traps are visited early in the morning and the insects 

 destroyed before they scatter again for the day. Burlap bands around 

 tree trunks attract many caterpillars as being good hiding places during 

 the day. These and munerous other special methods for the control of 

 insects are made us3 of, many being based on some peculiarity of habits 

 of the special pest for which they are used. 



Still other methods will be considered later, in connection with the 

 insects against which they are used. 



In order to make proper use of the above methods of Farm Practice, 

 a clear understanding of the life and habits of the insect to be controlled, 

 must be had. Failure in this might easily lead to doing just the wrong 

 thing. 



The control of insects is at the present time very unequally developed 

 for different crops. Naturally the insects of those which are most 

 valuable have been most carefully studied, those of less importance 

 having been given much less attention. Fruit and market-garden crops 

 have a high value and the insects which attack them have beeii carefully 

 investigated, though the area they cover is very small as compared with 

 the wheat acreage of this country, for example. Trees, bushes or other 

 plants, whether growing alone or in rows with cultivated land or grass 

 surrounding them are accessible as units on which to work, but a 10-acre 

 field of clover, wheat or any other crop, is a totally different proposition. 

 The former can be reached in all its parts by a spray or other treatment : 

 a wheat plant in the middle of a field may need treatment but to reach 

 it would probably cause a greater amount of injury than would be saved 

 by the treatment. 



Field crops and particularly grain crops therefore, present distinct 



