396 THE MONTHLY BULLETIN. 



Summary. 



The pear woolly aphis is distributed throughout the pear-growing districts of 

 northern and central California. 



Injury of marked degree is chiefly confined to trees under five years of age ; trees 

 the first and second years of their existence in the orchard suffer most severely, the 

 more weakly individuals either being killed outright or more often exhibiting degrees 

 of stunted growth. 



The injury is most severe on heavy soils that bake in summer and least severe 

 on sandy soils. 



The aphis lives the year around on the roots of pear, but may also spend the 

 winter and spring months on the European and cork elms, where it forms character- 

 istic baglike galls on the leaves. The journey from pear to elm and vice versa is 

 performed by winged aphids which are capable of traveling considerable distances. 

 The wingless forms on the root develop very slowly in winter and in midsummer 

 develop in as short a time as two weeks. In spring and fall the developmental 

 period is roughly a month, but varies according to season. 



Miscible oil, kerosene oil emulsion and distillate oil emulsion were used at proper 

 strengths with success in controlling aphis on the roots of young orchard trees. 

 Carbon bisulphide injected into the soil in liquid form with a pal injecteur proved 

 satisfactory, both on young orchard trees and in the nursery. There is some danger 

 to the trees in the use of this insecticide. 



The application of manure around the trees on the soil surface helps to conserve 

 moisture and assists in combating the aphis on heavy soils with a baking tendency. 



LITERATURE CITED. 



(1) 1916 — Baker, A. C. and Davidson, W. M. Woolly Pear Aphis. Journal Agr. 



Res. VI, 10. June 5. 



(2) 1916— Patch, Edith M. Elm Leaf Rosette and Woolly Aphid of the Apple 



Me. Agr. Exp. Sta. Bull. 256. November. 



(3) 1915 — Weldon, Geo. P. The Woolly Aphis as a Pear Pest. Monthly Bulletin, 



Cal. Hort. Com. IV, 9. September. 



(4) 1916 — Wisker, A. L. Blight-resistant Roots, etc. Monthly Bulletin. Cal. 



Hort. Com. V, 2. February. 



(5) 1915— Baker, A. C. The Woolly Apple Aphis. U. S. Dept. Agr., Bur. Ent. 



Report of the Secretary, 101. March. 



