10 BULLETIN 562, U. S. DEPARTMENT OF AGRICULTURE. 



It should be added finally that in view of the theory entertained 

 by some that lack of drainage or aeration in the soil is a cause of wilt, 

 experiments were made on the effects of deep plowing and subsoiling, 

 but the results were entirely negative. Dynamiting the soil accord- 

 ing to methods recommended was tried, with a view to destroying, 

 any hardpan or impervious layer beneath the topsoil, but no bene- 

 ficial action could be noted. 



CROP ROTATION AS A BASIS FOR THE CONTROL OF THE WILT. 



It has been seen that so far as known all species and varieties of 

 tobacco, both wild and cultivated, are readily destroyed by the wilt, 

 and it is well known that other plants belonging to the same family 

 are seriously attacked. Obviously none of these plants should be 

 grown on tobacco land affected with wilt. The parasite, however, is 

 by no means limited to solanaceous plants, and is now known to 

 attack members of no less than nine distinct families of the higher 

 plants, namely, (1) Solanacese (including tobacco, Irish potato, 

 pepper, eggplant, jimson weed, etc.), (2) Leguminosae (including 

 the peanut), (3) Balsaminacese, (4) Composite (including the com- 

 mon ragweed), (5) Euphorbiacese, (6) Pedaliacese, (7) Tropseolacese,. 

 (8) Urticacese, and (9) Verbenacese. It is probable that further 

 search will show that still other plants are attacked by this organism. 

 Outside of the Solanacea? the peanut and the ordinary ragweed are 

 of special importance in the flue-cured district. In parts of the dis- 

 trict peanuts are an important money crop and the ragweed (Am- 

 brosia artemisice folia) is extremely common on tobacco lands 

 throughout the district. Peanuts must be avoided and the ragweed 

 kept down if rotation of crops is to be effective in controlling 

 the wilt. 



CROP-ROTATION EXPERIMENTS AT CREEDMOOR, N. C. 



Beginning with 1911, experiments on the effectiveness of crop rota- 

 tion for the control of tobacco wilt have been conducted on a tobacco 

 field near Creedmoor, N. C, on which tobacco was practically a total 

 failure in 1910. The soil in this field is the Granville coarse sandy 

 loam and is rather uniform throughout except for a gall spot of 

 several square yards on the plat designated " F " in figure 1. The 

 plats slope away gently on either side of the turn row, which extends 

 through the center of the field. The drainage is good on all plats 

 except for small areas on the southern edge of plat 1 and on the 

 northern edge of plat 4, and there is but little chance for surface 

 drainage from one plat to adjoining ones. 



In these experiments the rotation and cropping systems included 

 nearly all of the more important crops adapted to the section, namely, 



