Diseases and Pests of the Apple and Their Control 211 



there will be the greatest hold-over effect against young 

 scale. This occurs just as buds are swelling. For badly 

 crusted infestation of scale, crude petroleum oils are' ef- 

 fective. As a rule, San Jose scale is now well controlled 

 by spraying. Control measures are directed particularly 

 to protect. the fruit from infestation. 



Oyster-shell scale (Lepidosaphes ulmi). (See Plate 

 XIII.) 



The oyster-shell is another common scale insect which is 

 not as serious, however, as the San Jose. The shape is 

 distinctive and resembles very closely a long narrow oyster- 

 shell. It is about Yg inch long, brown in color, although 

 sometimes grayish. Oyster-shell scale is not so widely dis- 

 tributed as San Jose scale nor is it usually a menace in 

 regions where the latter is serious. It seems to prefer a 

 higher altitude. 



The dormant lime-sulfur spray is not as effective in the 

 control of oyster-shell as of San Jose scale, yet in most 

 instances it seems to control both insects. Two or three 

 weeks after, the blooming period, the old oyster-shell scales 

 begin to loosen and the young lice start to crawl about. 

 Application of distillate oils, kerosene emulsion, or lime- 

 sulfur (1 to 35) is usually effective at this time. Nico- 

 tine sprays, 1 to 200, are also effective although somewhat 

 more expensive. 



Apple aphids. 



Four well-known species of plant-lice affect the apple. 

 Two of these, the oat aphis and the green aphis are green- 

 ish in color and feed chiefly on the foliage, causing it to 

 curl. The third species is commonly called the rosy apple 



