178 THE APPLE 



one premise to another must be effected artificially. Scale infesta- 

 tions are usually set up locally by the removal of the crawling young 

 from their birthplaces to other places on the legs and bodies of 

 larger insects and on the persons and clothes of orchard workers, 

 or by birds, plow animals, and possibly, for short distances, by 

 high winds. Scale-infested nursery stock is the commonest cause 

 of long-distance infestations. Thus it may readily be seen how im- 

 portant it is to protect oneself by guarding against the introduction 

 of nursery stock from infested territory. 



Allowing forty days to a generation, five full generations of this 

 scale are easily possible in the 214 days from April 1 to Octo- 

 ber 31. In all probability there are more. Marlatt, 1 estimating 

 200 females as the offspring of a single mother of the first gen- 

 eration, shows a possible progeny of 3,216,080,400 at the fifth 

 brood. These figures offer some explanation of the almost com- 

 plete annihilation in a single season of entire orchards where 

 conditions have been favorable for the multiplication of the scale. 



Characteristic injury of the San Jose scale. The effect of the 

 feeding of many scale insects is the slow sapping of the life of 

 the tree, or, in the case of fruit, a scurfy appearance, vivid discol- 

 oration, and consequent depreciation or worthlessness as a market 

 product. On smooth bark that is slightly infested, there is a red- 

 dish or purplish discoloration surrounding the insects, which ex- 

 tends through the bark to the wood proper. The sucking of the 

 insects results in a pitted, indented twig or limb. In heavy infes- 

 tations the scales overlap each other, literally incrusting the bark 

 so that it cannot be seen at all and giving the limbs the appear- 

 ance of having been dusted over with ashes. On a badly infested 

 tree in midsummer one can see with the naked eye thousands of 

 the yellow young crawling about. 



The apples themselves offer tempting conditions to the crawling 

 larvae and are freely infested where scale is present on the tree. 

 Even a few scales will discolor the skin of an apple, and a mod- 

 erate infestation will stultify the growth, often leaving the apple 

 cracked and misshapen. 



Treatment. The San Jose scale is most successfully destroyed 

 in the late fall or winter months. The tree is then dormant, and 



1 C. L. Marlatt, entomologist, United States Department of Agriculture. 



