TOBACCO WILDFIRE IN 1922. 17 



ment 11, where the plants were watered and inoculated every day or two. 

 The percentage of infection was fairly high on the Pjtox plot and the dust 

 plot. (The plants in the Bordeaux plot of this experiment were very 

 small and in poor condition on account of accidental burning by cyanide 

 gas which was used to fumigate the house. The low percentage of in- 

 fection on this plot is not significant.) In the next experiment (Experi- 

 ment 12) the plants were watered and inoculated less frequently and the 

 fungicide was applied oftener. The infection was thus reduced again to 

 less than 1 per cent. 



2. When the beds are exposed to frequent rains. The first rains wash 

 off the fungicide and later rains spread the bacteria. Even when the beds 

 are covered during rains there is usuallj^ considerable drip through the 

 sash between the glass. 



3. When the plants are growing very rapidly, as they usually are just 

 before setting begins. New leaves are produced so rapidly that many of 

 them \vill be left unprotected for several days if the application is made 

 only once a week. 



No definite interval of time between applications can be regarded as 

 safe. There are too many influencing factors. The only safe rule is to 

 keep all leaves covered at all times with the germicide. During the very 

 rainy season of 1922 no less than eight or ten apphcations would have 

 been necessary. Growers have also found it a good practice to dust 

 or spray the beds each time they are pulled over for setting. 



Amount of Material to be applied. — In apphdng the dust or spray the 

 only safe rule for judging whether enough has been applied is to note 

 whether all leaves are covered. The amount of material required to 

 produce a thorough covering will vary somewhat with the type of machine 

 used and the stage of growth of the plant. In the experiments recorded 

 above, in which a small rotary hand duster was used, it was found that 

 no less than a pound of dust for each application was required to cover 

 a square rod of plants when they were of a size suitable for setting. With 

 the compressed air sprayer which was used, 1| to 2 gallons of spraj' 

 material were found to be sufficient to cover the same area. 



Relative Cost of Spraying and Dusting. — At the local stores in Amherst 

 and Windsor lime cost $4.90 per barrel of 280 pounds, or, since a little 

 more if in smaller quantities, about 2 cents a pound, copper sulfate 11 

 cents a pound, Pyrox 20 cents a pound and copper-lime dust 10 cents a 

 pound. Using the amounts per square rod which are indicated above, the 

 cost of materials for eight applications would be as follows: — 



Bordeaux 4-4-50 . . . . . .12 cents per square rod. 



Pyrox 12-50 . . . . . ,58 cents per square rod. 



Copper-lime dust . . . . . .80 cents per square rod. 



Thus the cost of materials of a commercial fungicide such as Pyrox is 

 nearly five times as great as that of the home-made Bordeaux, while the 

 cost of the dust is nearly seven times as much. A good compressed air 



