328 Report of the Department of Entomology of the 



oil did not injure the foliage except when used pure and then 

 only slightly. So far as could be ascertained, temperature and 

 weather conditions had little effect on the results, as the effects 

 of spraying were practically the same under varying conditions of 

 heat and cold, sunshine and cloudy skies. 



The results of these experiments are also sufficiently definite 

 to indicate that kerosene oil may be used during the winter on 

 apple and pear trees at a percentage (40 per ct.) strong enough to 

 kill the scale without endangering the tree; but that it is imprac- 

 ticable for use on peach trees and dangerous to plum trees. 



II. METHODS OF COMBATING THE SAN JOSfi SCALE. 



There are two principal methods Of combating the San Jos6 

 scale in the orchard: First, fumigating the infested trees with 

 hydrocyanic 'acid gas; and second, spraying with some caustic 

 substance that will penetrate the scale and kill the insect beneath 

 or seal it over so firmly as to entirely smother it. 



FUMIGATION. 



Fumigation is practicable only for comparatively small trees 

 that can be safely cut back to about twelve feet in height and 

 about eight feet in diameter. Either a tent or a canvas box may 

 be used. The former is likely to be unsatisfactory because of the 

 difficulty in accurately estimating its cubic contents and the 

 trouble involved in handling. The box fumigator^ avoids these 

 difficulties and if not too large is more satisfactory. A modifica- 

 tion of the box type has been used by Prof. W. Gr. Johnson^ with 

 reported success. It consists of a box which is let down over the 

 top of the tree by means of a mast and pulley. The top of the 

 box consists of a canvas hood which adjusts itself to the height 

 of the tree. The cubic contents of the rigid part of the box can 

 be easily ascertained and the cubic contents of the extended 

 hood estijiiated. 



^A form of box fnmigntor is described in Bulletin 181 of this Station. 

 'TJ. S. Dept. Agr. Div. Ent., Bill. 20, u. ser., pp. 43^5. 



