THE POPLAR AND WILLOW BORER 471 



states that the use of arsenicals during July and August will kill the 

 majority of the beetles and reduce infestation in nurseries. In practice 

 it has been found that paris green and lead arsenate, even when used in 

 large quantities, have no effect in reducing the annual loss. At the time 

 when the writer began to look into this problem, in 1913, several large 

 nurseries in Xew York State had about decided to stop raising Carolina 

 poplars, although there was a steady demand for this stock. 



Early observations led the writer to the conclusion that the insect 

 could be destroyed by some contact spray applied to the trunks of the 

 trees in autumn, after the leaves had fallen, or in spring before the young 

 larvae had begun actively feeding. This seemed very reasonable, owing 



FlG. 124. AN EXPERIMENTAL PLOT OF CAROLINA POPLARS 



to the fairly exposed condition of the young larvae in their burrows. It 

 seemed that some oil emulsions would penetrate the outer bark or be 

 absorbed through the very small quantity of frass at the entrance 

 to the burrows, and would destroy the insects. Consequently, varying 

 strengths of miscible oils and kerosene emulsion, applied both in the fall 

 and in the spring, were experimented with. In order to secure a strong 

 penetrating fluid, it was felt that carbolineum avenarius should be given 

 a thorough trial. Very little is known about the constituents of this 

 preparation, and furthermore very little is known of its effects on actively 

 growing or on dormant trees. 



Experiments in 1913-14 



In the fall of 1913, seventy-six badly infested two-year-old poplar trees 

 were planted near the insectary at Cornell University (fig. 124). On Decem- 



