TOBACCO WILDFIRE IN 1922. 23 



however, wildfire began to appear again on the picked side of the field, but to a 

 greater extent beyond the forty-eighth row, where no picking had been done. The 

 field was harvested on August S. On that date the picked and unpicked sides of 

 the field were inspected by Mr. Arthur Hubbard, W. H. Davis, D. Potter, C. M. 

 Slagg, Dr. James Johnson and the wTiter, and it was the opinion of all that the un- 

 picked side showed much more wildfire than the picked side. Mr. Hubbard was of 

 the opinion that the east half would not have been worth harvesting if the disease 

 had been left to take its natural course. The loss in weight from removal of the 

 diseased leaves was not serious. As previously mentioned in this report there was 

 good evidence that when infection began again during the first few days of August 

 it came from bacteria which were in the soil. This source of infection cannot be 

 eliminated and will probably prevent this method of control from ever being en- 

 tirely successful. In view of the fact, however, that the season of 1922 was 

 usually favorable to the spread of wildfire, the results of the experiment are 

 encouraging. 



A similar experiment was conducted on a Round Tip plot at the Wind- 

 sor Station and with similar results. Growers who tried picking off af- 

 fected leaves are divided as to their opinion of the practical value of the 

 method. The degree of success varied according to the kind of tobacco 

 and method of harvesting. Chances of success are better in primed 

 tobacco because after harvesting starts the leaves are picked so rapidly 

 that the disease does not have an opportunity to get a good start, and 

 it also becomes increasingly difficult for the germ-laden soil to splash to 

 the first leaves. Field observations on the picking of leaves during 1922 

 lead to the following conclusion : — 



On the Shade Cuban, favorable results were almost uniforml}- obtained 

 and the disease was practically ehminated. On Havana and Roimd Tip, 

 where diseased leaves were removed, there was a considerable variation 

 in the results, with a majority of fields showing decided benefit. On 

 Broadleaf there did not seem to be anything gained by picking off the 

 leaves. 



For any one who contemplates this method of control it is recommended 

 that (1) the first inspection be m.ade as soon as the plants are estabhshed 

 in the field; (2) the leaves be picked off twice a week as long as any dis- 

 eased ones can be found; (3) sand leaves of diseased plants be picked also. 



Clinton and McCormick (2: 396) also experimented with removal of 

 diseased leaves and as a result were somewhat doubtful as to the benefits. 



Dusting the Plants in the Field. 



The value of dusting the plants in the field with copper-lime dust was 

 tried by two Massachusetts growers under the writers' supervision during 

 the season. 



Experiment 18. — Twenty-four acres in Had ley were first dusted with a four- 

 row traction duster, which was furnished by the Niagara Sprayer Company, on 

 July 6, when the plants were 12 to 18 inches high. The infection was bad in parts 

 of the field when the experiment was started. Four rows were left without dust. 

 There were very heavy rains on the 8th and the second application was made on 

 the 13th and 18th. During July there was very little spread of wildfire in any 



