28 MASS. EXPERIMENT STATION BULLETIN 195. 



economic point of view; but so far this has not been done. It may be 

 possible to apply some compound in a dry state to the field, and to do it 

 economically, but any application of a salt in solution would demand so 

 much water to obtain the requisite penetration that it would be out of 

 the question. So far a dry compound possessing the requisite fungicidal 

 action has not been discovered. Certain solutions and salts have been 

 used experimentally, but unfortunately none can be recommended for use 

 on a commercial scale. A brief statement of the results obtained in our 

 experiments with various compounds will be given below. It is believed 

 that control can be better obtained by changing the soil reaction to a more 

 acid condition by means of fertilization and cover-cropping, as has been 

 indicated. The whole question of the prevalence of root-rot and its infec- 

 tion in our fields is closely bound up with the question of soil reaction, and 

 it can hardly be profitably discussed apart from that problem. We have 

 been able, by the use of cover crops and acid fertilizer materials, to 

 "bring back" some heavily infested fields in a remarkably short time, and 

 have no hesitation in recommending the use of a timothy cover crop and 

 the non-application of lime to fields infected with the Thielavia root-rot. 

 Of course there may be danger of getting our soils into a condition too 

 acid for the best growth of tobacco, and judgment should be used in the 

 application of any raw acid materials. The grower should not forget 

 that "while a little may be a good thing, too much may be highly in- 

 jurious." An increase in the amount of phosphoric acid, applied in the 

 form of acid phosphate, has been found to have a beneficial effect, and 

 apparently does not advereely effect the quality of the tobacco. In our 

 experiments application of both "aged" and "raw" acid phosphate, in 

 amounts of 400 and 600 pounds additional to the acre, has given uniformly 

 good results, particularly on the lighter soils. 



Thielavia Root-rot Investigations. 



A statement of the results of some of our experiments having to do di- 

 rectly or indirectly with the Thielavia root-rot has been made in connection 

 with other lines of work. Some of the experimental work, while inter- 

 esting and fundamental from the scientific standpoint, can hardly be made 

 use of at present as a basis for the treatment of infested fields. As a 

 matter of record, however, a brief discussion of experiments is included 

 in this report. The first work undertaken was the attempt to control 

 the disease in the field by the application of chemicals to the soil. The 

 data presented represent the work of two years. The plots were located 

 on fields known to be heavily infested with Thielavia root-rot. The 

 substances used were formaldehyde, copper sulfate, iron sulfate, mercuric 

 chloride, potassium permanganate, sulfuric acid, sulfur, and " By- 

 product A, " a commercial preparation. With the exception of the sulfur 

 and "By-product A" the substances were all applied in solution. All 

 plots were in duplicate. The following table will indicate the amounts 

 applied, calculated to an acre basis. A check plot (no treatment) was 

 left between every two plots. 



