No. 6. DEPARTMENT OF AGRICULTURE. "' B7R 



gas, like Hydro-cyanic Acid gas (HCN), which is death to all animal 

 life; 2nd, Spraying or washing with some liquid material that will 

 kill or injure by actually coming into contact with the body of the 

 insect. 



At first thought fumigation would seem to be the more effective 

 of the two, for assuming that we have a gas and a liquid of equal 

 deadliness to a given organism, the fact that the gas will diffuse 

 evenly throughout any enclosure and penetrate where the liquid 

 will not, should make the gas the more effective. For this reason 

 HCN gas, being the most deadly, is the most effective insecticide 

 known, and is used generally in nursery fumigation where the San 

 Jose" Scale is present, on stock that can be put into a tight fumi- 

 gating house. 



There is, however, quite a difference in the practical work of 

 fumigating nursery stock or even small growing shrubs on the one 

 hand, and orchard trees on the other. The first essential in this 

 work is a gas-tight enclosure. Where trees and shrubs can be 

 easily taken from the ground, and in the course of events, are 

 so removed, this is a simple matter. In this case all that is neces- 

 sary is that they be placed in such an enclosure and the gas gener- 

 ated therein. When orchard trees are concerned, however, it is 

 necessary to enclose the trees instead of placing the latter in an 

 enclosure. This has been attempted in a number of instances, and 

 although quite successful from an effective standpoint, yet the cost 

 of outfit and labor and unwieldliness of equipment has caused its 

 early abandonment in practically every instance where tried outside 

 the citrus fruit belt of California. 



It was with the object of securing data, showing the relative 

 cost, rapidity, effectiveness, and injury (if any) to trees, that a 

 series of experiments in orchard fumigation were started some 

 months ago by the Division of Zoology of the Pa. Department of 

 Agriculture, and will be continued for some time. The general 

 outline of the work was as follows: Several blocks of young trees 

 from three to ten years of age, consisting of apple, pear, peach and 

 plum, were selected. Box frames were erected, having one side 

 removable, covered with tar paper and of such weight that they 

 could be readily carried from tree to tree. These were shoved over 

 the tree by opening the removable side, the computed amount of 

 matrials placed therein, the gas started to generate and the open- 

 ings immediately closed for half an hour. This gas was applied 

 at the rate of 20, 30, 40, 50 and 80 grams of Potassium Cyanide for 

 100 cubic feet of contents. The normal dosage in nursery stock is 

 30 grams per 100 cubic feet, but it was found that at the lower 

 strength, 20 grams per 100 cubic feet, every scale was killed. At 

 the normal dosage the cost of materials was about 5 cents each 

 for trees of 8 years, but the cost increases in proportion to the 

 cubic contents of the enclosures, which must have their outer walls 

 larger than the dimensions of the trees to be treated. The first 

 cost of apparatus is represented by the material and construction 

 of four boxes, as described, costing about four dollars each, a total 

 cost of sixteen dollars. Using four such boxes and three men 

 working, about seventy trees could be treated in a day of eight 

 hours. This cost of labor will raise the entire cost of treatment to 

 about 10 cents each for trees of the size stated above. As in the 



