THE WAR ON INSECTS 281 



oils or whatever else is depended upon to reach the 

 insects. After the scale has once hardened, none of 

 our summer applications that are safe on foliage can be 

 relied upon to kill. A large number of scales, soft as 

 well as armored, come under this general rule as to 

 development and treatment, and the gardener or farmer 

 who has insects of this kind to deal with, should know 

 their life cycle sufficiently well to know when to make 

 his applications. 



Scales that bear living young usually winter in the 

 partly grown condition and may be reached by appli- 

 cations which either penetrate through or under the 

 protective covering to the insect beneath. When repro- 

 duction begins the larvae are born singly, a few each 

 day, and this may continue for two or even three weeks. 

 By the time the last young emerge, the earliest are 

 already well grown and covered with scales, so there is 

 no time when a single application will reach more than 

 a small proportion of the infestation. If sprayings 

 could be made every third day so long as reproduction 

 continues, satisfactory results could be gotten; but 

 while this may be feasible in the garden and green- 

 house, it is not practical in the field and orchard. In 

 large greenhouses this method is often resorted to and 

 the scales on palms and other hot-house plants are kept 

 under control by frequent application of weak material. 



In the orchard much more drastic measures must be 

 resorted to, and in winter when the plants are dor- 

 mant, very caustic or very penetrating materials are 

 used. For caustics nothing is much better or more 

 generally effective than the lime and sulphur wash, 

 formed by combining one pound of ground or flowers 

 of sulphur with one pound of unslacked stone or shell 

 lime in three gallons of water. This combination is 

 made by boiling the lime and sulphur with just enough 



