TOBACCO WILDFIRE IN 1922. 11 



suggest themselves are (1) workmen, (2) insects, and (3) wind. Since 

 man}' isolated infections were discovered within a week or two after the 

 exceptional windstorm of June 12-13, it is possible that the organisms 

 may have been spread with the dust and sand which were blown in great 

 clouds over the vallej^ at that time. It has been shown above in this report 

 that dr}^, infested soil dusted over healthy plants may produce infection. 

 All observations of the summer confirm our previous conclusion that 

 the most important short distance disseminator of the disease in the field 

 is the rain, especially when accompanied by wind. It should be noted 

 here, however, that not every rainstorm is followed by a new outbreak 

 of wildfire. It was frequently remarked, especially during July, that 

 heavy short rains quickly followed by drying weather resulted in very 

 little spread of the disease. The ideal conditions for spread are (1) long- 

 continued rains, (2) rains followed by cloudy weather during which the 

 leaves do not become dry, or (3) periods during which the rains follow 

 each other closely. During June of 1922 we had a long-continued com- 

 bination of all three of the above conditions, which resulted in the worst 

 spread of wildfire which we have ever seen. 



CONTROL MEASURES. 

 Sterilization op Seed. 



Seed sterilization has been recommended by the writers because it was 

 thought possible that the bacteria might be carried on or with the seed. 

 Fromme and Wingard (3 : 20) of the Virginia Experiment Station, in fact, 

 are of the opinion that a large part of the infection is started from the 

 seed. Although there is no conclusive evidence in the Connecticut Valley 

 or elsewhere that such is the case, nevertheless the practice was recom- 

 mended as a precautionary measure. In 1921 formaldehyde was recom- 

 mended as the disinfectant (1: 75), but this year mercuric chloride was 

 recommended because it was found to be just as efficient and was less 

 likely to cause injury to the seed; therefore the following directions for 

 treating tobacco seed were sent out to tobacco growers before planting 

 time. 



Purchase corrosive sublimate tablets at any drug store. Dissolve one tablet in a 

 pint of water to make a Viooo solution. Use a glass jar. Place seed in a cheese- 

 cloth bag and soak in the solution for exactly fifteen minutes. Poke or stir occa- 

 sionally with a stick to insure thorough wetting of all the seed. Remove bag of 

 seed and wash thoroughly in water. Spread out seed in a warm room to dry. Store 

 seed where it will not become contaminated. Germination of the seed will not be 

 affected if directions are followed carefully. 



Many of the growers in 1922 used the corrosive sublimate treatment for 

 sterilizing their tobacco seed; and at the Windsor laboratory one hundred 

 and twenty lots of seed were sterilized by this method, and the germina- 

 tion before and after sterilization was tested. In no instance in the labora- 

 tory tests was there any injury from such seed treatment. 



I 



