14 CIRCULAR 692, U.S. DEPARTMENT OF AGRICULTURE 
tions previously mentioned. These sites were selected during the summer of 
1941 in fields where 90 to 100 percent of the tobacco was killed by wilt. Rates 
of 250, 500, and 1,000 pounds of urea (commercial grade containing 42 percent 
nitrogen) were applied in October 1941 or March 1942, corn was grown in 1942, 
and tobaceo in 1943. 
Corn made vigorous growth in all places. At one site where 500 pounds of 
0-10-10 fertilizer an acre was applied under the crop on plots in triplicate treat- 
ments of 250, 500, and 1,000 pounds of urea, corn averaged 27.1, 46.8, and 55.8 
bushels an acre, respectively. 
The extent of wilt on tobacco grown in 1943 is summarized in table 6. As 
shown, the 250- and 500-pound rates gave wide variations in wilt, and on most 
Block No. 
Rate in pounds 2s 
per acre Mean 
1 | 2 3 4 5 6 7 8 9 
| Percent | Percent| Percent| Percent | Percent Percen | Percent | Percent | Percent | Percent 
OAS NGS es eam Sk 1 42 59 73 65 81 | 45 | 59 | 53. | 90 2 63.0 
500 ne2 Sees ene 20 31 48 35 27 | 19 | 46 45 57 36.4 
000 Ss ee | 10 | 10 17 LZ a | 11 20 | 17 | 8 Bs) - 
| | | | 
1 Counts made Aug. 1 on plots of 70 to 110 plants each. 
2 Least significant difference at 1 percent level: 18.47. 
plots reductions in wilt severity were not adequate. The 1,000-pound rate gave 
sreater and more uniform reductions in disease severity, in that 20 percent was the 
maximum of wilt on any plot where this treatment was used. An average of 13 
percent wilt occurred on ali nine replicates, a reduction considered satisfactory for 
commercial use. 
The cost of 1,000 pounds of commercial-grade urea needed to treat 1 acre was 
$40, based on pre-war prices. Hence, soil treatment with this material appears 
economically sound in view of the increased corn yields obtained and the 
prevention of loss from wilt. This loss often exceeds $100 an acre. 
Soil type is known to affect results obtained with the urea treatment. The 
experiments reported here, which have been uniformly satisfactory, were con- 
ducted on sandy soils low in organic matter. Evidence has accumulated that 
tends to show this treatment to be of less value on the heavier soil types or on soils 
with a high content of organic matter. 
TaBLE 6.—Percentage of wilt on tobacco grown in rotation with 1 year of corn on 
soil treated with commercial urea (42 percent nitrogen) 
CHEMICAL TREATMENTS OF THE s@Hs 
Tests WitrH CHLOROPICRIN 
Chloropicrin was tested during the three seasons 1939 to 1941. The data 
reported in table 7 show the results of a test in which this chemical was injected 
to a depth of 7 inches in October 1939, the soil covered immediately with glue- 
coated paper, and tobacco planted in May 1940. In these and other trials good 
control but not eradication of the disease has been consistently obtained where 
glue-coated paper was used or where the upper inch or two of soil was wetted to 
confine the chemical. Less effective control was obtained when applications were 
made about 1 month before transplanting by injecting 1 ec. of chloropicrin at 
intervals of 1 foot on each side of the prepared list without paper or water seals. 
Further experiments failed to develop more practical methods of application. 
It was concluded that the chloropicrin treatment could be used to good advan- 
tage on plant beds, gardens, or other smail areas. Its cost was too high, how-- 
ever, and the technique of treatment too inconvenient for use in large-scale field 
operations. 
