TOBACCO WILDFIRE. 79 



tlie humidity is often very high under the sash. Water of condensation 

 dripping from the sash to the plants also appears to be responsible for 

 some spread. The beds should be run as dry and with as much air cir- 

 culation as possible. This tends to dry off the leaves, and helps reduce 

 the spread of the disease. In many instances where this was practiced 

 after infections were found, spread was much slower than when the beds 

 were closed tightly and very little if any air circulation permitted. Care- 

 ful attention to this matter will result also in stronger, better plants. 



Fertilizer Relations. 

 While fertilizer materials are not directly responsible for the disease, 

 there is apparently a relation between the rapidity of spread in the seed- 

 bed and the application of excessive amounts of some materials. This 

 was particularly noted in the case of nitrogen. Where excessive amounts 

 of nitrogen were applied to infested beds, the disease was much more 

 serious on the parts so treated than on those sections to which no addi- 

 tional nitrogen was applied. It was also noted that where growers applied 

 potash to infested beds the spread of the trouble was less than on sections 

 of the beds where none was applied. There have been no careful experi- 

 ments on the relation of fertilization to susceptibilitj^, but it is known 

 that excessive nitrogen applications force rapid succulent plant growth, 

 with little resistance to anj^ change in environment or disease invasion. 

 Potash is said to cause strengthening of the green parts of the plant, and 

 make it stockier and less susceptible to disease and change in environment. 

 This question cannot be considered settled, and experiments are under 

 way to check up on this point as related specifically to wildfire. 



Selecting Plants from Disease-free Beds. 

 Plants from infested seed-beds should never be set in the field, even 

 though the infection is slight. During the past season it was observed 

 that although plants in and around the infected areas were killed out 

 with formaldehyde, some infection, undeveloped at the time, appeared 

 later, and subsequently many of these beds became heavily infected. 

 Many of the lesions are so small and inconspicuous that they escape any 

 but the most careful observation. A single observation of the seed-bed 

 in the early part of the season is not an indication that the beds will remain 

 free from disease. This was sho^^^l by the fact that there were two and 

 possibh' three recurring epidemics this past spring, the last occurring 

 almost at the end of the setting season. It was the experience of many 

 growers that while the early set plants from their beds showed none of 

 the disease in the field, the late set plants developed the disease, and it 

 was also noted that many of the plants used for restocking showed the 

 trouble even when pulled from the same beds from which the field was 

 set, and that the disease occurred only on these plants. 



