ELM LEAF ROSETTE AND WOOLLY APHID OF APPLE. 341 



PREVENTIVE AND REMEDIAL MEASURES. 



The foregoing account of the habits and characteristics of 

 the woolly aphid will suggest certain measures to control it. 



The protection of seedling apples from infestation by the 

 woolly aphid while still in the nursery has heretofore been an 

 exceedingly difficult matter it would seem from the amount of 

 infested stuff that is yearly condemned. But with the knowl- 

 edge that the source of danger lies in the migrants from the 

 previously unsuspected elm leaf, it is seen to be possible to con- 

 trol the nursery stock by establishing nurseries at a safe distance 

 from susceptible elm trees or clearing out the elms from the 

 vicinity of large nurseries. As there are many places in the 

 country where the elm is not at all abundant this would often 

 be entirely practicable and where so would be the simplest and 

 most effective method of protection. As it is the seedling trees 

 that are most susceptible to injury and when attacked most 

 seriously damaged by the woolly aphid a method of protection 

 for the young trees while in the nursery is the most desirable. 



The raising of the elms and apples in the same nursery is thus 

 seen to be a hazardous proceeding and should be avoided. 



Again young orchards of clean stock set in parts of the coun- 

 try where the elm is not grown should be successfully protected 

 by excluding elms from the choice of shade trees. Indeed, the 

 matter of alternate hosts of the aphid enemies concerned should 

 always be borne in mind in planning the trees for an estate, and 

 only one of the two hosts necessary for the life cycle of a 

 migratory aphid planted, where the pest is a serious one. 



It is desirable that data concerning the relative susceptibility 

 of different varieties of apple should be accumulated with a 

 view to using the more resistant for root stock, if otherwise 

 practicable. 



In dealing with infested apple trees the aphid masses on trunk 

 and branch present no especial difficulty, and can be very readily 

 exterminated by the use of any of the washes recommended for 

 plant-lice, such as tobacco decoction, kerosene emulsion, a strong 

 soap wash (Formulas A, B, C, D), the only care necessary 

 being to see that the wash is put on with sufficient force and 

 thoroughness to penetrate the covering and protecting cottony 

 secretion. If the wash be applied warm, its penetration will 

 be considerably increased. 



