TOBACCO WILDFIRE IN 1922. 13 



The age of the seed or storage conditions may possibly play a role also, 

 as in many cases growers had no difficulty with their seed. A few cases 

 were brought to our attention where the injury was undoubtedly due to 

 incorrect procedure in the corrosive sublimate method. 



Data collected from growers who sterilized their seed during 1922 are 

 not conclusive as to the value of the treatment for preventing wildfire. 



As a result of our experience this past year, we are of the opinion that in 

 the Connecticut Valley, seed is, at most, a minor source of infection. 

 Nevertheless, this is a possibility which should not be lightly overlooked, 

 and growers should not save seed from plants which show wildfire infec- 

 tion. If this is found necessary, however, we believe the seed should 

 be treated with the corrosive sublimate. To avoid the difficulties dis- 

 cussed above, the beds should be sown with the dry seed. We do not 

 know how long the bacteria will remain on the seed, but it is unlikely that 

 there would be an}^ alive on seed two or three years old. By the use of 

 old seed the chance of infection from this source would be eliminated. 



Sterilization of Soil in the Seed-bed. 



Sterilization of the seed-bed soil with either steam or formaldehyde 

 was recommended by the ^vriters (1: 75) because it was thought possible 

 that the organism could live from one season to the next in the soil. Con- 

 siderable additional evidence that this is one of the ways in which it may 

 pass the winter has been obtained during 1922 and presented in a previous 

 part of this report. It is a common practice for growers to sterilize their 

 beds to kill weed seeds, prevent root rot and for other reasons; and many 

 beds were sterilized before the 1922 seed was sowed, a few in the fall and 

 more in the spring. Careful records were taken on fourteen beds in Massa- 

 chusetts which had been sterilized this year. Wildfire occurred in seven 

 of them and the others remained free. No conclusion can be drawn 

 from these data except that soil sterilization alone cannot be depended on 

 to give a clean seed-bed. It is unquestionable that sterilization of soil 

 by either steam or formaldehyde if properly done will kiU all the wildfire 

 bacteria in the soil treated, but it may not be so easy to eliminate the 

 possibility of getting it contaminated again from infested soil in the walks, 

 surrounding areas, tools, etc. These chances are perhaps greater where 

 soil is steriUzed in the autumn. Most growers use steam and consider it 

 cheaper. If steam is used, it should be applied for thirty minutes at 100 

 pounds pressure. Those who do not have boilers which will produce so 

 high a pressure may determine the proper length of exposure by burying 

 a small potato 4 or 5 inches below the surface of the soil under the pan 

 and applying the steam until it is cooked through. Only one of the four- 

 teen mentioned above used formaldehyde. Formaldehyde at a dilution 

 of Vso in water is applied at the rate of one-half to three-quarters gallon 

 to the square foot of surface. Some preferred to change the location of 

 the beds rather than sterilize the soil. In Massachusetts accurate records 

 were kept on eight beds, the location of which had been changed to places 



