20 BULLETIN 796, U. S. DEPARTMEITT OF AGPJCULTUEE. 



The trees treated were about 10 years of age and had suffered 

 heavily from borer attacks. They received 1 ounce each. On May 

 28, 1917, 15 were exahained. Nine showed no injury at all, 5 showed 

 traces, and 2 what was classified as slight injury. So far as the final 

 effect on the trees was concerned none of this injury was of impor- 

 tance. It was more than hitherto had been observed for this dose, 

 however, and while the reason is not entirely apparent it is felt 

 that it is best to make the application sufficiently early in the fall 

 to allow for complete evaporation before winter. This fact, cou]3led 

 with its less effective action, should be sufficient reason for avoiding 

 late application. When the application is made in the central lati- 

 tude as late as September 15, it probably would be wise to uncover 

 the trees after five or six weeks, and either allow them to stand open 

 for a time or refill with fresh earth. In fact, at the present stage of 

 our knowledge of the problem the writer is inclined to feel that this 

 might be a wise precaution to follow in every case. 



The varieties treated have included many of the leading commer- 

 cial sorts as well as a large number of unknown seedlings. So far 

 there has been nothing to indicate that one variety of peach is more 

 susceptible to the effects of the gas than another. 



A summary of the results obtained by one fall application of para- 

 dichlorobenzene is given in Table VI. 



IIELATION OF INJURY TO SOIL TYPE. 



No special relation between injury and type of soil has been discov- 

 ered in the use of j)-dichlorobenzene. Very porous soils probably 

 give a somewhat less concentrated vapor than very retentive soils, 

 but in practice the effect of soil type has not seemed important, al- 

 though the soils on which experiments were carried on have varied 

 from light sandy loams to heavy clay loams. 



INJURY TO APPLE. 



In August, 1916, an application of p-dichlorobenzene was made to 

 twelve 3-year-old apple trees at Springfield, W. Va. These trees were 

 treated with doses varying from 1 ounce to one-fourth of an ounce 

 each. All were quite well infested with S. Candida. The applica- 

 tion was made on August 23 and the examination on September 1-2. 

 Practically all the smaller larvae of the borer had been killed. The 

 more mature specimens working in deeper burrows were still living, 

 although several were affected noticeably by the gas. The trees were 

 severely injured, however. Apparently, the action of the gas on the 

 insect and the tree was almost simultaneous. Several of these trees 

 were so severely injured that they died the following season. On 

 another occasion an 8-year-old apple tree not infested with borers or 

 injured in any way was treated with an ounce of p-dichlorobenzene. 



