TOBACCO WILDFIRE IN 1922. 21 



by prompt action to keep the rest of the bed clean. This may be done 

 by immediately destroying the diseased spots by drenching them with a ^/io 

 formaldehyde solution. Not only the spot but all the plants within a 

 foot or two beyond it must be killed. This treatment was successful in 

 preventing further spread in one bed in Sunderland, in one in Hatfield and 

 two in Windsor, all of which were under the writers' constant observation 

 during the summer. Glass should be removed from all plants of the bed 

 which it is desired to save, because if they are left on, the fumes of the 

 formaldehyde will spread through the bed and burn the leaves with which 

 they come in contact. Plants should not be hoed out or pulled out before 

 treatment, since this only serves to spread the trouble. Plants around 

 the burned-out areas should be watched carefully for further spread. 

 Spraying or dusting should also be started at once if it has not been prac- 

 ticed previously. 



Removing All Plants from a Diseased Field and resetting with 

 Healthy Plants. 



Two fields have been under the careful observation of the writers during 

 1922 in which this practice was adopted, but in both cases it resulted in 

 failure. In one field in Hadley and one in North Hadley, when the plants 

 were about a foot high, they were found to be practically all infected. 

 All were removed from the field and after it had been harrowed the field 

 was reset with healthy plants. In both cases before the new plants were 

 ready to harvest, they became almost as badly infected as the old ones. 

 Apparently the pathogen remains in the soil and under favorable conditions 

 will infect the new crop. The grower can gain by this practice only when 

 the weather changes for the better during the growth of the second crop. 

 The same principle would apply also to the restocking of a field where 

 only a part of the plants were diseased. This was tried on a large scale 

 by a grower of shade tobacco at North Hadley, who removed only the 

 diseased plants (about 10 per cent) and restocked with healthy plants, 

 but failed to control the disease. The following experiment bearing on 

 this point was tried at the Windsor station : — ■ 



Experiment 15. — In one plot nineteen diseased plants were found ten days after 

 setting. They were all removed and replaced by healthy plants. Eleven out of the 

 nineteen resets developed wildfire later. 



During 1921 a number of growers practiced either partial or complete 

 restocking with healthy plants after diseased ones were removed, and 

 little or no wildfire appeared later in the field. The same was true of 

 some Connecticut fields in 1922. This apparent control may have been 

 due to weather conditions which were not favorable for infection of the 

 plants of the second setting. At any rate the results were contrary to 

 most of our experience of 1922. In view of the latter it seems question- 

 able whether restocking should be recommended. 



