8 MISSOURI AGRICULTURAL EXPERIMENT STATION BULLETIN 177 



for use. When used it is diluted with water in the same manner as the 

 commercial lime sulphur. 



Hydrocyanic-acid' gas was also tried in controlling San Jose scale on 

 orchard trees, and at present is used upon citrus trees for controlling citrus 

 scale. Where care was taken this method proved quite successful when 

 used on the deciduous fruit trees, but the cost of fumigating an orchard as 

 compared with spraying was so great that the former method has been 

 abandoned altogether. An air-tight box had to be constructed in such a 

 way that it could be moved from over one tree to another, or a large tent 

 had to be placed over the tree to be treated and the gas generated beneath. 

 Each tree had to be treated for about one hour. 



The treatment for San Jose scale must be applied while the tree is in a 

 dormant condition for the scale is so difficult to kill that a treatment, to be 

 effective, must be made so strong that it will also kill foliage. While the 

 tree is in a dormannt condition, the insects are easily reached and a strong 

 spray can be applied without any fear of damaging the foliage. Also, as the 

 insects pass the winter in a half-grown state, they are more easily killed 

 during the dormant season. 



In applying a spray for the scale, thoroness of the application is of the 

 utmost} importance. If twigs here or there are left without a coat of the 

 spray material, the insects which are on them will soon reinfest the tree. 



At the present time the standard spray for the control of the San Jose 

 scale upon deciduous orchard trees is lime sulphur. Commercial concen- 

 trated lime sulphur has a specific gravity of approximately 1.28. One gal- 

 lon of it is used to seven gallons of water which reduces the specific gravity 

 to 1.04. This solution is then applied with either a barrel or power spraying 

 machine during the dormant season. 



Besides controlling the San Jose scale with a dormant spray of lime- 

 sulphur, many other pests, such as Forbes scale and aphids are also con- 

 trolled. 



One of the important reasons why the San Jose scale is difficult to con- 

 trol is the fact that it attacks so many of the deciduous plants including 

 fruits, ornamentals and shade trees. 



Control on nursery stock. As has been previously explained it was 

 thru the infestation of nursery stock that the San Jose scale has become so 

 widely distributed and naturally the first place to start in the control of the 

 pest is upon nursery stock. 



Probably the most important means of controlling the scale upon 

 nursery stock has been the passing of laws requiring that all infested stock 

 be destroyed and the remainder treated under the direction of a competent 

 man. 



Before 1913 Missouri had no law controlling the growing or trans- 

 portation of infested nursery stock, and as a result much infested stock was 

 sold to Missouri farmers. In 1913 an effective law was passed and has been 

 vigorously enforced. 



Every state in the Union has a law similar to the Missouri law and they 

 have done much to prevent further spread of San Jose scale and other dan- 

 gerous insect pests and diseases as well. 



Practically all states require the use of hydrocyanic-acid gas in the 



