200 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 15 



FURTHER OBSERVATIONS ON THE USE OF PARADICHLORO- 

 BENZENE FOR THE CONTROL OF THE PEACH TREE BORER 



By Alvah Peterson, New Brunswick, N. J. 



(Withdrawn for publication in a bulletin) 



Mr. Glenn W. Herrick: Does it make any difference in the ap- 

 plication between the northern and southern half of the State? 



Mr. Alvah Peterson: September 15 for the northern half, and 

 October 1st for the southern half. Due to the fact that you never 

 find females after September 1st in the northern half, and in the southern 

 part after September 15th to 20th. 



President George A. Dean; The next is a joint paper by E. R. 

 Sasscer and C. A. Weigel. 



FUMIGATION WITH HYDROCYANIC-ACID GAS IN GREEN- 

 HOUSES ON A COMMERCIAL BASIS 



By E. R. Sasscer and C. A Weigel 



Although the use of Hydrocyanic-Acid Gas in greenhouses for the 

 purpose of controlling insect enemies is frequently referred to in en- 

 tomological literature, as well as in florist trade papers, there are very 

 few instances where an accurate account of fimiigation on a commercial 

 scale has been made. For the most part, these articles are of a general 

 nature, and the authors quite frequently fail to take into considera- 

 tion the effect that such factors as heat, moisture, light, exposure, quality 

 of the chemicals, and formulae employed would have on the final re- 

 sults. Many valuable plants have undoubtedly been injured on 

 account of inaccurate fumigation, and doubtless, it is on this account 

 that we find many florists prejudiced against the use of Hydrocyanic- 

 Acid Gas under glass. 



The work which has been carried on by the authors for the past 

 eleven years indicates that under proper conditions, Hydrocyanic- 

 Acid Gas is very effective in controlling the more important greenhouse 

 insects without appreciable injury to the infested plants. 



It is recognized that plants vary in their susceptibility to injury by 

 Hydrocyanic-Acid Gas, a problem which is increased in a house con- 

 taining a miscellaneous collection. Incidentally, plants in certain 

 stages of development bear considerable succulent growth which is 

 sxiie to be injured if the gas is used in sufficient concentration to kill 



