24 MASS. EXPERIMENT STATION BULLETIN 213. 



fields and the plants grew enormously. By the first of August the plants had grown 

 until the machine could not be drawn tlirough the field without serious damage tO' 

 the plants, and therefore no more applications were made. There was considerable 

 spread of the disease during August, until the crop was harvested about the middle 

 of the month. A comparison of the treated and untreated rows at that time showed 

 no difference in the amount of disease. No accurate counts were made, but a 

 cursory examination while walking between the rows did not indicate any benefit 

 from the two applications of dust. It was also noticed that there were dust-burn 

 spots on the treated leaves similar to those which have been previously described as 

 occurring in the beds. The owner feared that if the dusting were continued, the 

 spots might affect the market of the crop. 



Experiment 19. — Another grower in North Hadley dusted two fields with the 

 machine used in Experiment 18, but more frequent applications were made. Wild- 

 fire was not controlled, the results being similar to those of Experiment 18. 



Experiment 20. — On one of the Windsor Station plots Round Tip tobacco , 

 which showed a heavy mixed infection of wildfire and angular leaf spot on the 

 bottom two or three leaves when the plants were from 1 to 1 5 feet in height, a copper- 

 lime dust was twice applied to four rows, with a five-day interval between the first 

 and second treatments, no rain falling in the interim. Six rows were left untreated 

 for comparison. For about two weeks after treatment, the spread of the disease 

 in the dusted rows was practically nil, while in the undusted rows it spread steadily 

 and very rapidly. After this time three rainy days ensued, but purposely no more 

 dusting was done. At harvest time it was foimd that the amount of wildfire on the 

 dusted rows was only 15 per cent (estimated from partial count on cured tobacco) 

 less than on the rows which had not been dusted. 



No doubt, if the leaves in the field could be kept covered with dust all 

 the time, the disease could be controlled, but this would require more 

 frequent applications, and when the plants become large it cannot be 

 done without considerable breaking of the leaves. Control by this 

 method is probably possible, but not economically so. Further experi- 

 ments, however, are planned. It was found that the dust adhered much 

 better if applied early in the morning while the plants were still wet \\\t\\ 

 dew. 



Spraying with Bordeaux Mixture in the Field. 



Bordeaux mixture was tried with the idea that it would adhere to the 

 leaves more tenaciously and hence so many applications would not be 

 necessary as when dust was used. 



Experiment 21. — A field of 12 acres in North Sunderland was sprayed on July 

 11 with 4-4-50 Bordeaux. No further applications were made because the owner 

 feared that the material would remain permanently on the leaves and affect the 

 sale of the crop. An examination on August 14, when the crop was being har- 

 vested, showed that it was present in large enough quantity on many of the leaves 

 to give them a decidedly blue cast. A comparison of the sprayed and unsprayed 

 rows showed no difference in the amount of the disease. 



Clinton and McCormick (2: 395) experimented mth Bordeaux mixture 

 in a preliminary way and found that it retarded spread of the disease, 

 but they did not consider it practical because of cost and unknown effect 

 of the spray on the quality of the mature leaf. 



A few Connecticut growers tried spraying in the field in 1921 and 



