ORCHARD INSECTS OF THE PACIFIC NORTHWEST 



San Jose Scale 



The San Jose scale (Aspidiotus perniciosus Comst.) is potentially 

 capable of doing more damage than any other insect occurring in the 

 orchards of the Pacific Northwest. It not only renders the fruit 

 unmarketable, but it kills the twigs and limbs, and, if not controlled, 

 it eventually lolls the tree or at least so devitalizes it that it is worth- 

 less. Actually, the amount of damage done by the San Jose scale is 

 much less than that caused by the codling moth, because effective 

 control is easier, and fruit growers generally know the danger and 

 keep the scale under control. 



The scale insect feeds by sucking the plant juices from the twigs 

 and larger branches and from the fruit and foliage. It causes small 

 reddish spots, particularly on the fruit, and the presence of the scale 

 is often first made evident by the appearance of these spots (fig. 6). 

 The red discoloration also occurs 

 on scale-infested leaves and in the 

 bark. It cannot be seen on the 

 surface of the bark, but is disclosed 

 by cutting into infested twigs or 

 limbs. The bark has a roughened 

 and grayish appearance (fig. 7), 

 and if it is scraped a yellowish 

 liquid, coming from the crushed 

 bodies of the insects, appears. 

 Infestations are also manifested 

 by dead twigs scattered about the 

 tree and by the tendency of the 

 leaves on infested branches to re- 

 main on the trees during winter. 

 In irrigated districts, however, apPle leaves often remain on unin- 

 fested trees for at least a part of the winter. Although present meth- 

 ods of control are adequate and are keeping the scale in check, an in- 

 festation should not be regarded lightly. If spraying is neglected the 

 scales can become very numerous in a surprisingly short time under 

 favorable conditions, as the progeny of a single female may amount to 

 seveial million insects in one season. Laws in some States prohibit 

 the marketing of infested fruit except for the purpose of making by- 

 products, and quarantine regulations prohibit the entrance of infested 

 fruit into certain foreign countries. 



The San Jose scale is so named because it was first found at San 

 Jose, Calif. It is native to China and was evidently brought into 

 California with plants of some kind about 1870. It has since been 

 widely distributed on nursery stock and by other means, and at 

 present occurs in practically all the fruit districts in the Unijbed 

 States. It does more harm to apple and pear trees than to other 

 fruits, but is at times a serious pest of sweet cherry, peach, and prune 

 trees. It also attacks other deciduous fruit trees, nuts, and berries, 

 as well as many kinds of shade trees and ornamental shrubs, among 

 them the mountainash, currant, dogwood, elm, gooseberry, hawthorn, 

 lilac, linden, poplar, snowberry, willow, and the ornamental flowering 



291255° — 41 2 



Figure 6. 



Apples spotted by the San 

 Jose scale. 



