250 llErOKT Ui:' On-'ICE OF EXPElllMENT STATlU^'S. 



The effect of fumifrntion on nursery stock has been carefully studied 

 at the Maryland Station." During the exporinicnts at this station 

 3,()()() nursory troos were funiipitod, one-half of them in October and 

 the other half in April, all of the trees bein*;^ planted within two 

 weeks after funii«;ation. The trees employed in these experiments 

 were standard varieties of peach and apple. The time of exposure 

 varied from thirty minutes to one hour, and the amount of cyanid of 

 potash used varied from less than the ordinary amount to six times 

 that quantity. In some cases the trees were apparently injured by 

 the gas, but when these cases are compared with others in which a 

 larger amount of cyanid was used without injury it is apparent that 

 some* other agencies, probably unfavorable weather conditions or 

 unsatisfactory methods of planting, are responsible for part of the 

 injury. The actual amounts of cyanid used per cubic foot were 0.2, 

 0.3, 0.4, 0.5, 0.75, 1, and 1.5 grams for different lots. In these experi- 

 ments it was noted that peach trees are apparently more resistant to 

 the effect of hydrocyanic-acid gas than apple trees. This must be 

 due to the naturally greater tolerance of peach trees for this gas, since 

 apple trees fumigated at the same time were even more completely 

 matured than the peach trees. This fact has also been observed in 

 experiments in New Jersey. Certain varieties of apple appear to be 

 more resistant to the gas than others. Thus, Yellow Transparent was 

 uninjured while Ben Davis, Maiden Blush, York Imj^erial, and 

 AVinesap were somewhat affected. In the spring experiments no 

 injury from fumigation was observed even when excessive amounts 

 of cj'^anid were used and the period of exposure prolonged to one 

 hour. The 3,000 trees used in these experiments were free from San 

 Jose scale, but other infested trees treated at the same time for com- 

 parison showed no living scale after fumigation. 



The New York State Station ^ recognized the effectiveness of the 

 fimiigation method in destroying scale insects in orchards and has 

 devoted considerable attention to this problem, particularly to the con- 

 struction of inexpensive and practical fumigation boxes for orchard 

 trees. During these experiments it was found possible to construct 

 tight and satisfactory boxes wdiich could readily be manipulated by 

 two men and which possessed the considerable advantage over tents for 

 the fumigation of orchard trees in that the cubic contents of the box 

 could readily be determined. It was possible, therefore, to use the 

 same amount of chemicals for each tree covered with the box, thus 

 avoiding the necessity of changing the amount for each tree and 

 weighing the cyanid of potash in the field after a calculation of the 

 cubic contents of the tent. It is believed that the slight cost of the 



a Maryland Sta. Bui 105. 



6 New York Sta. Buls. 181, 194, 202. 



