TOBACCO DISEASES AND THEIR CONTROL. 5 



or the bacterial leaf spots have recently caused concern, is presented. 

 In the case of damping-off and root-rot the use of new soil or 

 sterilized soil will ordinarily suffice. 



(1) Plant beds should preferably be placed a considerable dis- 

 tance from the location of the seed beds or fields of the previous year 

 and away from tobacco-curing barns and weedy areas. 



(2) No tobacco refuse (trash) or stems should be used as fertilizer 

 on seed beds. Refuse should preferably be cleaned up and destroyed 

 before seed beds are started. 



(3) Plant-bed frames should be made of new material, or the old 

 material should be disinfected by painting or sprinkling with some 

 disinfecting solution such as formaldehyde or corrosive sublimate. 



(4) If new seed-bed covers are not used, the old cloth covers should 

 be sterilized by boiling one hour, and sash should be disinfected with 

 the frames. 



(5) If new land is not used for seed beds — i. e., woods lands, new 

 breaking, or sod — the soil for the seed beds should be sterilized, pref- 

 erably by steaming for at least 30 minutes. 



(6) In case the tobacco seed to be used is likely to be infested with 

 wild-fire or black-fire it should be disinfected with corrosive subli- 

 mate (1 part to 1,000 parts of water). Place the seed in a cheese- 

 cloth bag, dip it in the solution, and stir it about for 10 to 15 min- 

 utes. Rinse thoroughly with pure water and dry as rapidly as 

 possible. This method of sterilization can be used only with seed 

 sown in the soil without previous sprouting, since sprouting is other- 

 wise interfered with. Silver-nitrate (1 to 1,000) treatment for 15 

 minutes gives as good disinfection as corrosive sublimate and permits 

 sprouting of the seed before sowing. 



(7) Do not sow the seed too thickly (1 ounce to each 800 to 1,000 

 square feet is usually sufficient). Do not overwater the plants, and 

 ventilate frequently by raising or removing the covers, especially 

 when glass covers are employed. 



(8) Inspect the beds at intervals for diseased plants, and if any 

 are noted destroy them at once and soak the infected area with form- 

 aldehyde solution (1 to 25). Carefully avoid these infected areas 

 when weeding or pulling plants, since the parasites are readily spread 

 at such times. If infection is general in the seed bed it is safest to 

 procure healthy plants from other sources for transplanting. 



THE STERILIZATION OF SOIL FOR PLANT BEDS. 



The sterilization of seed beds b} T steam, using the inverted-pan 

 method, gives the most satisfactory results (fig. 2). Surface firing, 

 roasting, and the formaldehyde-drench methods are useful under 

 certain conditions or in the absence of facilities for steam steriliza- 

 tion. The principal benefits of soil sterilization are the killing of 

 parasites which may be harbored in the soil, such as those which 

 cause damping-off and root-rot, and the killing of weed seeds. By 

 bringing about other changes in the soil, however, a considerably 

 more uniform and rapid growth of the seedlings ordinarily results 

 (fig. 3). 



To steam beds by the inverted-pan method, a boiler, pan, and con- 

 necting hose or pipe are required. The boiler should have sufficient 

 capacity to discharge a continuous flow of steam at a pressure of at 



