Orchard Pests and their Control 357 



orchardists have to contend are comparatively few. 

 Altitude and aridity certainly have something to do in 

 rendering our orchards immune to a large array of pests 

 that are common to orchards in lower altitudes both East 

 and West. But the codlin-moth and the green and the 

 woolly aphis are so abundant and persistent that they 

 make up in a measure for the lack in number of species. 



Only the more important insects are included in the 

 following discussion. All of the information in regard to 

 them has been abridged from the numerous publications 

 of Professor C. P. Gillette, entomologist of the Colorado 

 Agricultural Experiment Station. 



It should be borne in mind that the term "plant-diseases " 

 as discussed in these pages refers only to those orchard 

 troubles that are caused by the attacks of small plants. 

 While these plants are mostly microscopic and low in the 

 scale of development, they are just as truly plants as are 

 the trees upon which they live. If one can think of the 

 bacteria and fungi as being microscopic weeds, it will help 

 to an understanding of what might otherwise seem mys- 

 terious. It is difficult, for example, for the beginner to 

 understand how the death of blighted pear trees is due to 

 the growth of small plants within the tissues of the trees. 

 Yet that such is the case has long been known. 



All persons know that insect pests are live animals; 

 but not all are familiar with the fact that insects have 

 different modes of feeding. Any one can see that cabbage- 

 worms chew their food and gradually devour large areas 

 of cabbage leaves. But how about plant-lice, scale insects, 

 mites, and a large number of similar insects? These pests 

 are usually small, and their feeding-habits are not so 



