JOMALOFAGKIOmRALlSEARCH 



Voi,. XV Washington, D. C, October 21, 1918 No. 3 



EFFECT OF HYDROCYANIC-ACID GAS UNDER VACUUM 

 CONDITIONS ON SUBTERRANEAN LARViB 



By E. R. Sasscer, Chief Inspector, and H. L. Sanford, Entomological Inspector, 

 Federal Horticultural Board, United States Department of Agriculture 



INTRODUCTION 



The advisability of fumigating all imported nursery stock at the port 

 of arrival as a requirement for entry has been under consideration for 

 the past five or six years. It is generally recognized that hydrocyanic- 

 acid gas under proper temperature conditions is effective against prac- 

 tically all insects likely to be introduced, provided these pests are neither 

 hermetically sealed in the tissues of the plants nor secreted in the soil 

 around the roots. 



Under normal conditions from five to seven million ornamental plants, 

 such as azaleas, rhododendrons, aucubas, conifers, box bushes, bays, etc., 

 are introduced annually with balls of earth around their roots. Needless 

 to say, it is impossible satisfactorily to inspect and safeguard plants of 

 this type without removing the soil from the roots. Inasmuch as prac- 

 tical horticulturists have strongly advised against this procedure on 

 account of its effect on the plants, the only safe course appeared to be 

 fumigation with hydrocyanic-acid gas under vacuum conditions. With 

 this end in view, experiments, listed in Table I, were conducted, in which 

 various dosages and exposures were used, in order that the effectiveness 

 and the degree of safety which might be obtained by fumigating all 

 introduced plants having balls of earth around their roots could be 

 determined. 



EXPERIMENTAL PROCEDURE 



Owing to the variable amounts of water in the soil surrounding the 

 roots of balled plants at the time of arrival, it w.as considered advisable 

 to fumigate subterranean larvae buried at various depths in dry, moist, 

 and soaked soil.^ 



The water content of the moist and of the soaked soil compared favor- 

 ably with the condition of the soil around the bulk of plants at the time 

 of arrival. Very few plants would survive shipment in soil as free from 

 moisture as that used in the dry experiment. Furthermore, the soil 



' The soil used consisted of i part of manure, i part of peat, and 4 parts of loam. 



Journal of Agricultural Research, Vol. XV, No. 3 



Washington, D. C. Oct. ji, 1918 



pu Key No. O-x 



