12 



CIRCULAR 2 7 0, U. S. DEPT. OF AGRICULTURE 



essary also to scrape rough bark from the trees and to clean out any 

 cankers in order that the spray may reach all parts of the trunk and limbs . 

 On medium or heavy infestations of the San Jose scale, lubricating 

 oil emulsion must be used at a dilution containing about 4 percent of 

 oil, to obtain satisfactory results, although a dilution containing 3 

 percent of oil may be sufficient for very light infestations. Lime- 

 sulfur solution must test at least 4%° Baume for most infestations. 



This requires 11 gallons of a 

 concentrate testing 32° 

 Baume to make 100 gallons 

 of spray. Very light infesta- 

 tions may be held in check 

 with a dilution testing at 

 least 3K° Baume, requiring 

 8 gallons of 32° Baume con- 

 centrate for 100 gallons. (For 

 schedules of oil and lime- 

 sulfur dilutions, see pp. 73 

 and 71). 



If the dormant-season ap- 

 plications have not proved 

 adequate, summer-strength 

 applications of about 1 per- 

 cent oil emulsion, such as 

 are used for the codling moth 

 and red spider, or of lime- 

 sulfur concentrate (1 gallon 

 to 50 gallons) as employed 

 for combating the apple 

 powdery mildew, should con- 

 siderably reduce the amount 

 of fruit spotted by the scale, 

 if applied during June or 

 August, when most of the 

 young scales are present. 



Oystershell Scale 



The oystershell scale (Lepi- 

 dosaphes ulmi (L.)) is found 

 throughout the Northwest, 

 but occurs most commonly west of the Cascade Mountains and is 

 seldom seen in the irrigated valleys of the interior. It is readily dis- 

 tinguishable from other scale insects by its characteristic shape 

 (fig. 10). The apple is a favorite food plant of this scale, but it also 

 lives on a great variety of fruit and shade trees, ornamental shrubs 

 and plants, and on native trees, such as willow and dogwood. Its 

 effect on the tree and fruit is similar to that of the San Jose scale, 

 and heavily encrusted trees or limbs may be killed. 



Figure 10. 



Twig encrusted with the oyster- 

 shell scale. X 4. 



LIFE HISTORY 



If the old scales on the bark be turned over during the winter, they 

 will be found filled with small, pearly white, oval eggs (fig. 11). 



