Aprils, 1920.] Agricultural Gazette of N.S.W. 285 



The Sterilization of Tobacco Seed-beds 



by Steam* 



G. P. DARNELL-SMITH, D.Sc, F.LC. F.C.S., Biologist, and 

 C. J. TREGENNA, Tobacco Expert. 



The most di-eaded disease in tobacco seed-beds m New South Wales is: 

 "blue mould " due to the fungus Peronospora hyoscyanii. It usually makes 

 its first appearance when the seedlings have five or six leaves, blotching these 

 with irregular yellow patches or giving the whole leaf a pale shade of the 

 same colour. On turning over the leaf and examining the under side, the 

 region of the discoloration is found to be covered with a fluff of a pale violet 

 tinge — hence the name "blue mould." Jhis fluflf, when examined under the- 

 microscope, is found to consist of vast numbers of branched fungus threads,. 

 each branch bearing at its extremity a pale lemon-shaped spore. The spores 

 are produced in countless millions and serve to spread the disease with 

 extraordinary rapidity when once it has made its appearance. The complete 

 lif(( history of the fungus is not known ; but on account of the success which 

 is claimed from the treatment of seed-beds in general by the use of steam, it 

 was thought worth while to give the method a trial on tobacco seed-beds — 

 more particularly as it has been tried for similar purposes in. America. The 

 apparatus used by the writers was made to a specification drawn up by Mr. 

 A. Brooks, Works Overseer, its main details being taken from an American 



publication. 



Design of the Steaming Apparatus. 

 The apparatus consisted of a heavy frame of wood 12 feet by 6 feet. The 

 outer framework was of 4 inch x 2 inch spotted gum and it was covered on 

 one side only with |-inch tongued and grooved beech boards. Nailed to the 

 inside of the frame was a 6 inch x ^ inch blade of spotted gum, bevelled on 

 the lower edge. All joints were made steam-tight,, and when earth was 

 banked over this blade the whole apparatus was steam-tight. Fixed 

 through the frame at about 1 2 inches from each corner were 3 inch x | inch 

 ring bolts, with nuts and washers on the lower ends. Stout poles passed 

 into these enabled four men to shift the frame from place to place when 

 necessary. In the centre of one end of the frame,^ fixed with back-nuts and 

 gaskets, was a |-inch steam connection about 7 inches long and projecting 

 on the outer end sufficiently to connect with the steam, ho.se union. 



Its Application. 



To make effective use of this apparatus one requires an engine capable of 

 maintaining a pressure of 70 lb. per square inch ; such engines are possessed 

 by many tobacco growers, being used for purposes of irrigation. The 

 remaining requirements are a cock for regulating the steam, several lengths 

 of steam pipe, and about 25 feet of steam hose |-ineh diameter. The piping 



