TOBACCO WILDFIRE IN 1922. 19 



witli the parasitic ha('t(>ria woro sprinkled over all tlie plants every three 

 oi- four days. Sucli a method of inoculation is much more drastic than 

 would occur under natural conilitions in the beds of the average tobacco 

 grower. If the treatment here recommended is faithfully carried out by 

 the grower, we believe that in the large majority of cases no wildfire will 

 be found in his beds. Even if there are occasional infected plants in the 

 bed, the treatment is not a failure. The removal of diseased plants from 

 the field will be much easier if there are only a few of them. Even if 

 they are not all removed, the amount of final infection may be expected 

 to be less if there are only a few centers from which it can spread. 



Will Clean Beds give Clean Fieldsf — Clean beds are not an absolute 

 guarantee that no wildfire will appear in the fields planted from such 

 beds. During the season of 1922 in at least six instances the writers had 

 convinced themselves bj^ thorough and frequent inspection that the seed- 

 beds of certain growers were entirely free from wildfire, but the disease 

 developed later in the fields planted from these same beds. (Read the 

 paragraph above on ''Dissemination" for more details.) Such cases, 

 however, should not encourage any one to believe that no benefit is de- 

 rived from keeping the seed-bed clean. The worst and the most wide- 

 spread field infections have usually come from the bed. Starting with 

 clean plants in the field is not the whole measure of success, but it is a 

 long start toward it. 



Success by Practical Growers. — During the season of 1922 the writers 

 made frequent inspections and kept careful records on the seed-beds of a 

 number of growers. Untreated checks were not left in any case, and for 

 this reason the results are not entirely convincing. They were unable 

 to find wildfire in any of these beds where the plants were kept constantly 

 covered with the fungicide. On the other hand, it did appear in the beds 

 of many who dusted or sprayed a few times, or started to treat only after 

 the disease became e\adent, or used only a scant amount of material. 



Value of an Arsenical in the Fungicide. — In the first test some of the 

 fungicides, both the dry and the liquid, contained an arsenical. This 

 arsenical not only was found to be of no value for the control of wildfire, 

 but frequently caused injury to the plants. There seems to be no reason 

 for adding an insecticide. 



/)(/.s/ Burn and Spray Injury. — Heav.y application of dust or copper 

 spray frecjuently causes some injury to the plants. It has been commonly 

 noted in the experimental beds at Amherst that the plants in the check 

 plots appear healthier (except for the wildfire) and larger than in the treated 

 plots. Growers have frequently called the writers' attention to this con- 

 dition in their beds. Sometimes it is much more marked than at other 

 times. Frequently it cannot be observed at all. Certain conditions of 

 the plant or its environment must be responsible for this variation, but it 

 is not as yet known just which conditions favor and which prevent such 

 injury. 



Dust l)urn is evidenced on the leaves by small dead spots of one-eighth 



I 



