PLANT INSPECTION IN MISSOURI 11 



the result that a great deal more good was accomplished than ever before. 



Ninety-three nurseries, located in forty different counties, were in- 

 spected, eighty of which were certified. A total of 1,469 acres of nursery 

 stock was growing in 1919-20. Sixty-seven cases of foreign stock con- 

 taining 442,000 plants were received in six different counties and inspected. 

 Eighty nursery inspection certificates; twenty-three dealers certificates; 

 157 growers permits and 121 agents permits were issued. 



During the year 1919-20 eight nurseries were found to be slightly in- 

 fested with San Jose scale. In every case the nursery infested was in 

 close proximity to a heavily infested orchard and as the season in 1919-20 

 was favorable for the growth and spread of the scale some of the near-by 

 nurseries had become infested to some extent, but none seriously. As in 

 previous years every precaution was taken to prevent its further spread 

 and to eradicate it from the nurseries and the near-by orchards. 



The method most generally used in eradicating and preventing the 

 spread of San Jose scale on nursery stock and the one recommended by 

 the Plant Inspection Service is to destroy all visibly infested stock and 

 treat all other stock, subject to infestation, by either hydrocyanic acid 

 gas or by dipping it in a miscible oil. The hydrocyanic acid gas treatment 

 is more commonly used than the latter. In using this gas this method is 

 followed: 



One fluid ounce of sulphuric acid having a specific gravity of at least 

 1.83 is placed in an earthernware crock, wooden bucket, or tub; then 3 

 fluid ounces of water are added. In this mixture 1 ounce, by weight, of 

 fused cyanide of potassium, 98-99 percent pure, is added. The above 

 amounts are used for every 100 cubic feet of space. In fumigating tender 

 growing plants, the above formula is too strong and has to be weakened. 

 For dormant trees, mills, elevators and the like the 1-1-3 formula is recom- 

 mended by both the United States Department of Agriculture and prac- 

 tically all of the state experiment stations. 



In fumigating nursery stock an air tight box or house is necessary. 

 The trees are placed in the box or house. The water and sulphuric acid 

 are mixed in an earthern jar and the jar placed in the box or house. The 

 potassium cyanide is then dropped in and the box or house closed just as 

 quickly as possible. The hydrocyanic acid gas which is generated is deadly 

 poisonous and the person doing the fumigating must be very careful not to 

 breathe any of it. It requires about 45 minutes to fumigate nursery stock, 

 although some authorities say that better results can be obtained by let- 

 ting the stock remain an hour. At the end of this time the fumigating box 

 or house is opened and the gas allowed to escape and in from 15 to 20 

 minutes the trees can be safely removed. 



It is never advisible to fumigate trees while they are damp or wet. It 

 is claimed that under such conditions the gas is more likely to injure the 

 stock. However, the writer's experiments to date fail to corroborate this, 

 though they do show that less scale is killed under those conditions. 



Some states require by law that all nursery stock grown within its 

 borders or shipped in from outside nurseries be fumigated, and, as a result, 

 all of the larger nurseries in the United States have constructed special 

 fumigating houses or boxes. 



