TOBACCO DISEASES AND THETR CONTROL. 7 



roasting process consists in principle of shoveling about 4 inches 

 of the seed-bed surface soil upon an iron pan under which a fire is 

 maintained and heating it sufficiently to convert most of the mois- 

 ture to steam before replacing the soil. 



For the formaldehyde-drench method use 1 gallon of formaldehyde 

 to 50 gallons of water, sprinkling this over the beds at the rate of 

 about 50 gallons to every 100 to 150 square feet of seed-bed surface 

 and regulating the flow so as to allow the solution to soak into the soil 

 to a depth Of at least 4 inches. The soil must then be given several 

 clays to dry out and all fumes of formaldehyde allowed to disappear 

 before sowing the se'ed. For this reason the formaldehyde method 

 is quite unsatisfactory unless its application can be made a consid- 

 erable time before the time of sowing, since weather unfavorable for 















SsS^S^bSSS^VS 



RjnR. 





' ■■'* \?» 









'-^S'-ilii 



■" ' "■ ii iWJBMWWMBBi 



,_ 



££$%£&& 



lllfll 





SeISmShI 



v."' . 







. 



Ll_~ 



, 





SSKSSi. 



-.2 



Fig. 3. — Growth of plants on soil steam-ed and not steamed. The area to the left of 

 center was steamed ; the area to the right was not steamed. Steamed soil produces 

 healthy plants. 



drying may delay sowing. Fall applications of the formaldehyde 

 drench, however, may sometimes be used to advantage. 



In the following pages the parasitic diseases are roughly grouped 

 according to the parts of the plant primarily affected. The non- 

 parasitic diseases and those due to saprophytes are in separate 

 groups. 



STEM OR STALK DISEASES. 



DAMPING-OFF OR BED-ROT. 



Description. — A rot of young plants starting in the stem of the 

 plant near the soil surface in plant beds is usually referred to as 

 damping-off. This disease may appear at almost any stage of growth 

 of the seedlings in the bed, and, as will be pointed out later, a very 

 similar condition may be met with on isolated plants in the field. 

 Usually, however, the disease is most likely to occur when the plants 

 become much crowded and the ventilation at the surface of the soil 

 is very poor during periods of wet weather. Under such conditions 

 the disease spreads rather rapidly, ordinarily in circular areas from 

 isolated centers of infection. The plants generally topple over, the 

 whole stem and leaves becoming decayed, although in other cases 



