180 SHADE-TREES IN TOWNS AND CITIES 



stages occurring on infested trees at the same time. A sin- 

 gle pair, starting under favorable conditions in June, may 

 have descendants to exceed one thousand million before 

 snow is on the ground. 



Experience has shown that the most effective way to 

 control the San Jose Scale is to spray with oil or soap emul- 

 sions as soon after the middle of October as possible. At 

 that time, the functions of the leaves have been accom- 

 plished and any scorching of the foliage by the spray will 

 not affect the tree itself. It is best to choose a sunshiny day 

 for the work, to use a nozzle that will give a fine spray and 

 to apply the mixture until the twigs begin to drip. 



Scurfy Scale {Chionaspis furfurus Fitch). — This scale 

 usually infests the poplars and the maples among the shade- 

 trees. It is a very pale gray, almost as broad as long, with 

 a yellowish point or head. Beneath this scale the eggs are 

 found during the winter, and in June they hatch into pur- 

 plish-colored larvae, which suck the plant juices. There is 

 only a single brood which matures in September, and is 

 rarely abundant enough to do very much injury. 



This scale is thinner than most others of the armored 

 forms, and may be reached by caustic sprays in the winter. 

 If no winter application is made it is necessary to wait until 

 the eggs hatch in June, and then apply whale-oil soap or 

 kerosene emulsion. 



Oyster-Shell Scale {Mytilaspis pomorum Bouche) . — Like 

 the San Jose scale this insect attacks orchard-trees mostly, 

 but is also present on shade-trees. It derives its name from 

 the resemblance to one of the very elongate types of oysters. 

 It winters in the egg state under the scale, and in May or 

 June the eggs hatch into minute yellow atoms that set and 

 begin to form small scales. These suck the juices of the 



