12 MISSOURI AGRICULTURAL EXPERIMENT STATION BULLETIN 177 



RESULTS OF EXPERIMENTS WITH HYDROCYANIC-ACID GAS 



Because of the large amount of damage being done in Missouri by the 

 San Jose scale, and in order to help the fruit grower and nurserymen to 

 better control the scale and thus lessen the danger of further dissemination 

 of the pest, the writer began a series of experiments in the fall of 1915 

 with reference to the control of the scale upon nursery stock. 



Some of the nursery stock in the state which was found to be infested 

 with San Jose scale was brought to Columbia where the experiments were 

 conducted. 



. ' The primary object of the investigation was to determine if possible 

 the most practical, efficient and cheapest method to use in controlling the 

 scale on nursery stock with the least injury to the trees or plants. 



In Missouri there are a number of nurserymen who grow nursery stock 

 on a small scale and do not care to go to the expense of building an ex- 

 pensive fumigating house or box and besides many object to using hydro- 

 cyanic-acid gas because of its very poisonous nature. Several of these 

 nurserymen have asked repeatedly about the possibilities of dipping nurs- 

 ery stock in a lime-sulphur wash or a miscible oil for the control of San 

 Jose scale. 



Some of the nursery stock which was used in the experimental work at the Missouri Agri- 

 cultural Experiment Station 



Method of procedure. First, during the fall of 1915 the following 

 number of fruit trees and plants were obtained: Apple, 356 trees; peach, 

 164; pear, 52, and plum, 52. All of the fruit trees were two years old. Of 

 the apple trees obtained, 260 were heavily infested with San Jose scale and 

 86 of the peach trees were also heavily infested. The trees were dug in the 

 fall after the leaves hati fallen and shipped to Columbia. Most of the 

 scale-infested trees showed marked weakness caused by the ravages of the 

 pest; otherwise all of them were in good condition. The trees were heeled 

 in the fall and left until March 21 and 22, 1916, when they were given the 

 different treatments. None of the trees died during the winter. 



The work was continued during 1917. On April 5, 1917, the following 

 two-year-old trees were obtained, all of which were heavily infested with 



