99 



On Nursery Stock. — In the dormant state, the San Jose scale may 

 be carried to any distance on nursery stock, cuttings, and scions. It is 

 thus that it was transported from its original home in China to the 

 shores of California, and thence to all the principal fruit-growing sec- 

 tions of the United States. 



Means of Control 



Natural Checks. — Several natural agencies very materially check 

 the multiplication of the San Jose scale, but it multiplies so rapidly 

 that its numbers increase greatly notwithstanding. The chief of these 

 checks are climatic conditions, predaceous and parasitic insects, and 

 fungous diseases. 



Under adverse climatic conditions may be included winds, rains, 

 and extremes of heat and cold. Blustering winds and dashing rains 

 sweep many of the crawling young from the bark. Not infrequently 

 more of them may be found on the ground under badly infested trees 

 than on the trees themselves, and very few of these ever get back to 

 the tree on find other food plants. The scale does not thrive in those 

 parts of our country where the summers are long and excessively hot 

 and dry; and it has failed to establish itself in some of the northern 

 states, where the winters are long and severe. In a few instances a 

 very heavy mortality, resulting from these unfavorable conditions, 

 has been noticed in Illinois. In St. Clair county in the spring of 1902, 

 from 21 to 69 per cent of the scales which might have been expected 

 to live were found to be dead. This loss was attributed to the hot, 

 dry weather of the preceding summer, when temperatures reached 

 109° F. in the shade. Again, in the spring of 1911, counts of dead and 

 living scales made from different parts of Illinois showed that from 45 

 to 98 per cent of the hibernating insects were dead — a mortality due, 

 for the most part, to the severity of the preceding winter, during 

 which temperatures of —24° F. were reached at various places in the 

 state. Such extremes, however, are so rare in Illinois that the San 

 Jose scale ordinarily suffers little from such causes. 



Several lady-beetles and their larvce feed on the San Jose scale; 

 a number of hymenopterous insects parasitize it ; and it is also attacked 

 by fungous diseases. These natural enemies have controlled it very 

 effectively in a few regions, but only where climatic conditions are 

 favorable to their rapid and continuous multiplication, as in Florida and 

 California. In Illinois, and in nearly all the interior states, the cli- 

 mate is adverse for so much of the time that little assistance can be 

 expected from these natural enemies. 



