116 MASS. EXPERIMENT STATION BULLETIN 175. 



before again handling healthy seedhngs. If these precautions are taken, 

 according to CUnton, a considerable amount of mosaic infection will be 

 avoided at the time of planting. 



It has been repeatedly shown that care should be exercised during 

 early cultivation not to cut the roots or touch broken or abraded leaves 

 of plants and then subsequently touch other plants, for the disease is 

 very easily transmitted in this way, as the fine hairs or epidermis may be 

 broken and infection occur. The amount of infection due to cultivation 

 is, however, in the writer's opinion, slight, but as much care as is com- 

 mensurate with efficiency should be exercised by the workmen during 

 cultivation. 



The advisabiUty of the removal of diseased plants is open to question, 

 and on the whole it cannot be economically recommended unless the 

 plants can be replaced early in the season. As has been previously pointed 

 out, the disease may be carried from plant to plant when topping, etc., 

 and the subsequent sucker growth will become mosaic. At this time, how- 

 ever, the commercial leaves are of such size that their value will not be 

 materiall}^ impaired, but if possible, to prevent a certain amount of infec- 

 tion, only healthy or diseased plants should be topped at any one time. 

 Of course, all suckers developing later, diseased or otherwise, should sub- 

 sequently be removed from all plants, not only for the sake of the com- 

 mercial leaves, but to prevent a ragged looking field, giving the appear- 

 ance of a large amount of mosaic. 



It has been very difficult to associate any particular type of soil with 

 general occurrence of mosaic disease, but on the whole, from data gathered 

 at different times, the heavier types of soil in the valley appear to be more 

 generally favorable for the production of mosaic-diseased plants. This 

 cannot be definitely stated, however, as the data are complicated by the 

 fact that in some cases, on both heavy and light soils, the condition of 

 the soil as regards organic matter present enters into the question. The 

 writer has observed that on many heavy soils where comparatively large 

 amounts of organic matter are present during certain seasons, in com- 

 parison with similar soils deficient in organic matter, the mosaic is much 

 less. To a certain extent this holds true also for the lighter soils. The 

 exact relation existing between the mosaic disease and these factors is 

 at present not enough studied to warrant definite conclusions, but Sturgis 

 (loc. cit.) was of the opinion that clayey soils were favorable to its pro- 

 duction. It is a significant fact that many of our tobacco soils are some- 

 what deficient in organic matter, however. Well-cultivated and conse- 

 quently well-aerated soils do not apparently produce as many mosaicked 

 plants as those which are not well cultivated. 



Another factor which should be carefuUy attended to is that of the 

 moisture conditions in the bed at the time the plants are pulled. It should 

 not be too moist nor too dry, as in either case the roots are apt to be 

 broken and infection from handling result more certainly than when the 

 plants are removed with a minimum of root injury. 



