CONTROL OF TOBACCO WILT IN" THE FLUE-CURED DISTRICT. 7 



RELATION OF THE PHYSICAL AND CHEMICAL PROPERTIES OF 

 THE SOIL TO THE WILT. 



The second line of attack in searching for a practical method of 

 controlling the wilt was to determine whether the soil could be 

 treated by chemical or physical methods which would destroy the 

 organism causing the trouble or weaken its activity. In 1904 a series 

 of field plats on infested soil at Creedmoor, N. C, was given various 

 chemical treatments before being set to tobacco. Heavy applica- 

 tions of powerful disinfectants, including several salts of copper, 

 formalin, corrosive sublimate, permanganate of potash, carbolic 

 acid, iron sulphate, and sulphur, were tried. Strong acids and alkalis 

 and excessive applications of potash, nitrogen, and phosphoric acid 

 also were tested. None of the treatments gave any promise of suc- 

 cess in practical tobacco culture. In 1910 another series of field 

 tests with chemicals was made on a diseased field near Creedmoor, 

 including a more extensive study of the effect of acid and alkaline 

 conditions on the disease. The effects on the wilt of soluble forms 

 of calcium, magnesium, silicon, aluminum, iron, and manganese 

 were tested, but without results, these tests being based on the 

 assumption that the wilt is not to be feared in soils containing large 

 amounts of clay. Various fertilizer treatments were tried, only 

 materials tending to produce alkaline conditions being used on some 

 plats, while on others only substances favoring an acid reaction were 

 employed. For example, one plat received per acre 200 pounds of 

 carbonate of potash, 600 pounds of basic slag, 250 pounds of nitrate 

 of soda, 500 pounds of cottonseed meal, and 2,000 pounds of burned 

 lime, while another received equivalent amounts of sulphate of potash, 

 acid phosphate, ammonium sulphate, and acid sodium sulphate. 

 None of these treatments produced any decided effect on the amount 

 of wilt. 



In the following year, in order better to control the experimental 

 conditions, a large number of glazed-tile cylinders 2|- feet long and 

 2 feet in diameter were set in the ground so as to leave about 3 

 inches projecting above the ground level. The cylinders were in- 

 stalled at West Raleigh and at Creedmoor. The pots were filled to a 

 depth of about a foot with bottom earth taken from the holes in 

 which the pots were placed, after which about 8 inches of subsoil and 

 8 inches of topsoil from a diseased tobacco field at Creedmoor were 

 added. All tests were made in duplicate and each cylinder contained 

 four plants. In continuation of previous work, tests were made with 

 mixtures of varying proportions of sandy and clay soils ; with ordi- 

 nary wilt soil, to which were added separately the chief chemical con- 

 stituents of clay ; with plants grown from seeds without transplant- 



