18 MISSOURI AGRICULTURAL EXPERIMENT STATION BULLETIN 177 



As to the effectiveness of hydrocyanic-acid gas upon San Jose scale, the 

 above tables show that it might not in every case kill all of the scale, es- 

 pecially when used at a strength weaker than 1-1-3. When used at a weaker 

 strength it will kill a large percentage of the insects but not enough to 

 recommend its use. 



From the summary it is readily seen that more of the trees died when 

 treated with the stronger hydrocyanic-acid gas than with the weaker. It is 

 a known fact that plants treated with a high strength of hydrocyanic-acid 

 gas will be injured and if the hydrocyanic-acid gas is too strong it will kill 

 the trees. Whether or not it takes the gas longer than a month to effect a 

 tree enough to kill it, is not known but it stands to reason that if the gas 

 does injure a plant,, the 1-1-3 strength would cause more injury than the 

 1 / 2 - 1 /2-l ;i /2 strength. 



As has been shown, the greater strength gave better results in con- 

 trolling the scale than the weaker and as far as killing the trees is con- 

 cerned, there is not enough difference in the two strengths to amount to a 

 great deal. Since the control of the scale is of the most importance, it is 

 undoubtedly advisable to use the 1-1-3 formula when fumigating nursery 

 stock. 



Another very important thing that was brought out in this work is the 

 effect of hydrocyanic-acid gas upon wet and dry plants. It is the general 

 belief among nurserymen that if plants are treated with hydrocyanic-acid 

 gas while wet, or damp, the moisture on the plant will absorb a large 

 quantity of the gas, which in turn, will cause a great deal of burning and 

 injury to the plant. It will be noticed that in this work, a larger percentage 

 of those plants treated dry died than those treated wet which is contra- 

 dictory to the general belief of nurserymen and experiment station workers. 



In treating plants with ether to stimulate 

 growth, a larger dose of ether must be used if 

 plants are damp or the exposure must be longer 

 if the same results are derived as would be ob- 

 tained if the plants were dry. This may also 

 be true of hydrocyanic-acid gas and as the re- 

 sults obtained indicate, a larger dose of hydro- 

 cyanic-acid gas must be used on damp plants 

 to obtain the same results as on dry plants with 

 a smaller dose. Also, fewer scale were killed 

 upon the damp trees than on the dry, which 

 indicates that possibly the same thing holds true 

 in regard to animals as to plants. 



Since the scale was killed better on stock 

 treated dry than on stock treated wet, and as 

 the destruction of scale is of prime importance, 

 nursery stock should not be fumigated with 

 hydrocyanic-acid gas when wet, even tho the 

 injury to the plants may be greater when treat- 

 ed dry. 



A well constructed fumigating 

 house. It is built of tongue and 

 grooved lumber and cleats cover 

 the joints on the outside 



