68 MASS. EXPERIMENT STATION BULLETIN 203. 



Last year, when to the best of our knowledge the disease appeared in 

 rather widely separated localities in Massachusetts, it was felt that the 

 spread might not be rapid, but in 1921 the infection was quite general 

 throughout the State, with apparently local centers of heavy infection, 

 the only beds or sections free from the trouble being those in outlying 

 districts. 



Unless the disease is controlled there is no question but that it will 

 become a serious matter and the cause of considerable loss to the tobacco 

 growers. It is apparent from data collected this year that nearly all, if 

 not all, of our field infections originate in the seed-beds; hence the pro- 

 duction of healthy seedlings becomes a matter of prime importance. 



Weather conditions have a great deal to do with the spread of the 

 trouble, as has been shown not only in the South but in Massachusetts 

 as well. But even under favorable conditions timely control measures 

 are necessary to combat the trouble. 



It is not known how in 1921 wildfire became so generally distributed 

 throughout the different sections, nor why we apparently had two or 

 three successive infections during the seed-bed period. In order to deter- 

 mine these points, and to find, if possible, some methods of prevention, 

 eradication or control, investigations were begun by the writers in the 

 spring of 1921. These investigations are by no means completed, but 

 sufficient data, especially on seed-bed control, have been secured to war- 

 rant a preliminary report. 



APPEARANCE OF THE DISEASE. 



The symptoms or signs of the disease are prominent and very easily 

 recognized. The spots may be found on the leaves at any stage in the 

 development of the plant from the time the first seed-leaves appear to 

 full maturity. They are sometimes found on the seed-pods, but have not 

 been observed on stalks or roots. They are usually noticed first in the 

 seed-bed. The typical spot on the leaf in its first recognizable stage is a 

 circular chlorotic area, yellowish green, of a lighter color than the sur- 

 rounding leaf surface, and less than a quarter of an inch in diameter. 

 Within the next twenty-four hours a small brown or whitish dead speck 

 of less than pin-head size marks the center of the lesion which, under 

 conditions favorable for the disease, has now increased to a quarter of 

 an inch or more, is of a more decided yellow color, and forms a prominent 

 halo about the central dead area (Plate I, Fig A). Both the central 

 browTi dead spot and the yellow halo now increase in size, and within 

 a few days the affected part may be a half inch or more in diameter. 

 The central brown dead part maj^ or may not be surrounded by a water- 

 soaked translucent band, depending apparently on moisture conditions. 

 In very humid times the entire spot is sometimes soft and water-soaked. 

 The most constant and dependable character is the yellow halo which 

 persists in all stages of development. Any number of spots may occur 



