624 INSECTS AFFECTING VEGETATION 



eased field to a healthy field may spread the disease. One of these 

 ways is by washing. In some cases a field now healthy may be pro- 

 tected from higher land that is infected by proper arrangement of 

 dykes. 



A second means of soil conveyance is by tools. A cultivator or 

 a hoe used in an affected field carries myriads of germs. If such a 

 hoe be used in an unaffected field these germs will be distributed 

 and the disease spread. This means of spreading is largely within 

 the control of the farmer. All that is required is such thorough 

 cleansing of tools that no possibility of conveying the germs re- 

 mains. First, the dirt should be knocked off, then wiped off and the 

 implement finally cleaned by being thoroughly wet with a solution 

 consisting of two per cent formalin or five per cent carbolic acid. It 

 is difficult to insure complete protection against spread by the feet 

 of animals and man, but every possible precaution should be ex- 

 ercised in this particular. 



Every diseased plant is veritable culture ground for the germs. 

 Therefore every such plant and every part of such a plant should be 

 destroyed by fire. Pull the plants up by the roots, getting all of the 

 roots possible. Let them dry and then burn them. This precaution 

 in a badly diseased field diminishes the nourishment at the disposal 

 of the germs and will probably enable the land to recover more 

 rapidly. Burning is, however, especially important where but a few 

 plants in a field are affected. Prompt action here may materially 

 lessen the rapidity of spread of the disease in the field. It should be 

 borne in mind that every particle of sick plant burned means the 

 destruction of millions of the germs. (N. C. E. S. B. 188.) 



The germs reside in the soil. The possibility of killing them 

 in the soil therefore arises. Experience with other diseases which in 

 a similar way winter in the soil leads to but slight hope that any 

 method of soil sterilization will ever be practicable. This germ is 

 different from others that have been experimented upon, however, 

 and the importance of the problem demands that a thorough trial 

 be made. 



The fact that the seed-bed seldom if ever bears diseased plants 

 indicates that the heat generated by burning the bed, suffices to kill 

 the germs. 



A long rotation of crops, one that will bring tobacco back upon 

 the affected field only after an intervening period of several years, 

 perhaps after a period of eight or ten years, seems at present to be 

 the only recourse for one whose field is now infected. Even with 

 this precaution it is doubtful whether the disease can be completely 

 eradicated. 



The tobacco wilt germ has not been proved to be injurious to 

 other crops, and tobacco-sick soil can probably be safely planted 

 with any other crop, with the possible exception of such close rela- 

 tives of the tobacco as the Irish potato and the tomato and egg- 

 plant. 



A Wilt Resistant Kind of Tobacco. The one means of over- 

 coming the wilt which is most promising to farmers who own af- 



