42 FARMERS BULLETIN 804. 



enemies, and migrates from the grape to Viburnum in early fall. 

 When so abundant as to require treatment, any of the contact in- 

 secticides may be used. 



CLEAN CULTURE. 



As the reader will have learned, most aphids have a -winter and 

 early spring host plant, and from this they migrate to other plants, 

 on which they subsist for several weeks or months during the summer. 

 In most instances this alternation of food plants is essential to the 

 life of the species, and in general the aphids are most troublesome 

 in regions where alternate hosts are present in abundance. Often 

 one or more of the host plants are of little or no economic importance 

 in the localit}^, and in some cases are troublesome weeds. The de- 

 struction of worthless plants is desirable and should serve materially 

 to reduce the aphids in question. Thus, in the case of the rosy aphis, 

 the alternate food plants of which are species of plantain, the destruc- 

 tion of these in and about orchards is especially desirable, and should 

 be a part of the remedial work against this pest in localities where it 

 is more or less chronically injurious. 



WASHINGTON : GOVERNMENT PRINTINC OFFICE : 1917 



