42 THE SA>r JOSE OB CHES^ESE SCALE. 



The most commonly infested ornamentals are purple-leaved plnm, Cratarffitig^ Japa- 

 nese qoince, mountain ash, red-twigged do^^ood. and Eo.'ta rugom. Poplar, wiUow. 

 Persian lilac, Cotonea^er, elm (both American and European), and osage orani:e 

 have been found thoroly incmsted by the insects, especially when growing near 

 infestei trees. 



Of the plauti^ which are repK)rted as noninfested in this list 

 probably many of them may he subject to slight or occasional 

 infestation. Notwithstanding- the San Jose sc-ale's wide range of food 

 plants, strangely enough certain varieties of pear seem to be almost 

 never attacked, and are practically exempt from injury. This hold- 

 true also, to a less extent, with different varieties of other fruits. 

 The striking illustrations are the Leconte and Kieffer varieties of 

 pears, and the reason for this immunity is difficult to explain. Differ- 

 ences in the density and textiu-e of bark could hardly account for it. 

 because that would scarcely protect new and comparatively tender 

 growth. A notable instance of the immunity of the Leconte pear is 

 seen in the little grove connected with the insectary of this Depart- 

 ment. This grove has been thickly planted to pear and apple trees, so 

 that the branches are interlacing all the time, and it has been pretty 

 badly infested with the San Jose scale off and on for ten years, and 

 yet the 10 or 12 Leconte trees have been clean the whole time, while 

 the rest, representing different varieties of pear, apple, peach, and 

 plima. have died out or have been replaced, some of them over and 

 over again. 



CITRUS FRUirS AXB THE SAX JOSE SCALE. 



The susceptibility of the orange and lemon and other citrus plaut> 

 to the San Jose scale is a matter of great interest to citrus growers. 

 In c-atalogs of the food plants of the San Jose scale the orange and 

 lemon and other citrus fruits are listed, notably in Mrs. Fernald's 

 Catalog of Coccidfe. The facts on which this statement is based are 

 rather meager, and. when examined, do not warrant anv grave fear> 

 of injury to the ordinary cultivated citrus fruits. It is well known 

 that the San Jose scale will infest rather freely the trifoliate orange, 

 a hedge plant somewhat closely related to the orange and lemon. 

 Some trifoliate trees, for example, on the Department groimds, are 

 now rather thickly covered by the San Jose scale, but even in the case 

 of this hedge plant the infestation is, as a rale, not serious, and. 

 according to Mr. Gos<ard. the plant seems to throw the scale off as it 

 grows. The tirst undoubted example of San Jose scale on orange was 

 on certain hybrid sorts produced by crossing the trifoliate orange 

 with the sweet orange, and was received in 1903 from Mr. Gossard 

 from Florida. Mr. Gossard stated that in a single instance where a 

 small .sweet oi-ange tree interlaced with the branches of a Ixidlv 

 infested trifoliate orange the former had matured perhaps half a dozen 

 San Jose scales. 



